Showing papers in "Journal of Plant Growth Regulation in 2005"
TL;DR: Evidence is reviewed for a variety of long-distance signaling pathways involving hormones and nutrient ions moving in the xylem sap that allow regulation of plant growth, development and functioning, and particularly shoot water status, as distinct from stress lesions in growth and other processes as a reaction to perturbations such as soil drying.
Abstract: In this article we review evidence for a variety of long-distance signaling pathways involving hormones and nutrient ions moving in the xylem sap. We argue that ABA has a central role to play, at least in root-to-shoot drought stress signaling and the regulation of functioning, growth, and development of plants in drying soil. We also stress the importance of changes in the pH of the leaf cell apoplast as influenced both by edaphic and climatic variation, as a regulator of shoot growth and functioning, and we show how changes in xylem and apoplastic pH can affect the way in which ABA regulates stomatal behavior and growth. The sensitivity to drought of the pH/ABA sensing and signaling mechanism is emphasized. This allows regulation of plant growth, development and functioning, and particularly shoot water status, as distinct from stress lesions in growth and other processes as a reaction to perturbations such as soil drying.
343 citations
TL;DR: Studies revealing hormonal control of fruit development using tomato as a model system with emphasis on molecular genetics are reviewed.
Abstract: Fruit development is a complex yet tightly regulated process. The developing fruit undergoes phases of cell division and expansion followed by numerous metabolic changes leading to ripening. Plant hormones are known to affect many aspects of fruit growth and development. In addition to the five classic hormones (auxins, gibberellins, cytokinins, abscisic acid and ethylene) a few other growth regulators that play roles in fruit development are now gaining recognition. Exogenous application of various hormones to different stages of developing fruits and endogenous quantifications have highlighted their importance during fruit development. Information acquired through biochemical, genetic and molecular studies is now beginning to reveal the possible mode of hormonal regulation of fruit development at molecular levels. In the present article, we have reviewed studies revealing hormonal control of fruit development using tomato as a model system with emphasis on molecular genetics.
270 citations
TL;DR: Quantitative genetics and functional genomics approaches will contribute to the elucidation of genes and proteins that control seed dormancy and germination, including components of the ABA signal transduction pathway.
Abstract: Seed dormancy is an adaptive trait that improves survival of the next generation by optimizing the distribution of germination over time. The agricultural and forest industries rely on seeds that exhibit high rates of germination and vigorous, synchronous growth after germination; hence dormancy is sometimes considered an undesirable trait. The forest industry encounters problems with the pronounced dormancy of some conifer seeds, a feature that can lead to non-uniform germination and poor seedling vigor. In cereal crops, an optimum balance is most sought after; some dormancy at harvest is favored because it prevents germination of the physiologically mature grain in the head prior to harvest (that is, preharvest sprouting), a phenomenon that leads to considerable damage to grain quality and is especially prominent in cool moist environments. The sesquiterpene abscisic acid (ABA) regulates key events during seed formation, such as the deposition of storage reserves, prevention of precocious germination, acquisition of desiccation tolerance, and induction of primary dormancy. Its regulatory role is achieved in part by cross-talk with other hormones and their associated signaling networks, via mechanisms that are largely unknown. Quantitative genetics and functional genomics approaches will contribute to the elucidation of genes and proteins that control seed dormancy and germination, including components of the ABA signal transduction pathway. Dynamic changes in ABA biosynthesis and catabolism elicit hormone-signaling changes that affect downstream gene expression and thereby regulate critical checkpoints at the transitions from dormancy to germination and from germination to growth. Some of the recent developments in these areas are discussed.
268 citations
TL;DR: It is concluded that it is highly unlikely that ABA regulates all the genes associated with cold acclimation; however, it definitely regulates many of the genesassociated with an increase in freezing tolerance.
Abstract: The freezing tolerance or cold acclimation of plants is enhanced over a period of time by temperatures below 10°C and by a short photoperiod in certain species of trees and grasses. During this process, freezing tolerance increases 2–8°C in spring annuals, 10–30°C in winter annuals, and 20–200°C in tree species. Gene upregulation and downregulation have been demonstrated to be involved in response to environmental cues such as low temperature. Evidence suggests ABA can substitute for the low temperature stimulus, provided there is also an adequate supply of sugars. Evidence also suggests there may be ABA-dependent and ABA-independent pathways involved in the acclimation process. This review summarizes the role of ABA in cold acclimation from both a historical and recent perspective. It is concluded that it is highly unlikely that ABA regulates all the genes associated with cold acclimation; however, it definitely regulates many of the genes associated with an increase in freezing tolerance.
177 citations
TL;DR: In this article, the influence of air vapor pressure deficit (VPD) and plant fruit load on the expansion and water relations of young tomato fruits grown in a glasshouse were evaluated under summer Mediterranean conditions.
Abstract: The influence of air vapor pressure deficit (VPD) and plant fruit load on the expansion and water relations of young tomato fruits grown in a glasshouse were evaluated under summer Mediterranean conditions. The contributions of phloem, xylem and transpiration fluxes to the fruit volume increase were estimated at an hourly scale from the growth curves of intact, heat-girdled and detached fruits, measured using displacement transducers. High VPD conditions reduced the xylem influx and increased the fruit transpiration, but hardly affected the phloem influx. Net water accumulation and growth rate were reduced, and a xylem efflux even occurred during the warmest and driest hours of the day. Changes in xylem flux could be explained by variations in the gradient of water potential between stem and fruit, due to changes in stem water potential. Misting reduced air VPD and alleviated the reduction in fruit volume increase through an increase in xylem influx and a decrease in fruit transpiration. Under low fruit load, the competition for assimilates being likely reduced, the phloem flux to fruits increased, similarly to the xylem and transpiration fluxes, without any changes in the fruit water potential. However, different diurnal dynamics among treatments assume variable contributions of turgor and osmotic pressure in F3 and F6 fruits, and hypothetical short-term variations in the water potential gradient between stem and fruit, preventing xylem efflux in F3 fruits.
119 citations
TL;DR: Genetically modified plants constitutively overexpressing ABA biosynthesis genes have been produced and analyzed over the last 6 years, and in some cases these plants have been found to have elevated ABA concentrations, leading to altered stomatal behavior and increased seed dormancy.
Abstract: Mutant plants deficient in the phytohormone abscisic acid (ABA) are typically unable to control their stomatal behavior appropriately in response to water stress, leading to a “wilty” phenotype. In plant species showing strong seed dormancy, ABA deficiency of the seed results in a second clearly recognizable phenotype, that is, early germination. Mutants selected by means of this latter character are often collectively termed “viviparous.” These two broad classes include mutants that are defective in their ability to synthesize ABA. A number of these genetic lesions have been assigned to specific steps in ABA biosynthesis and have been invaluable in elucidating many important features of the pathway. Most of the genes encoding ABA biosynthetic enzymes have now been cloned and their expression has been studied and manipulated. Genetically modified plants constitutively overexpressing ABA biosynthesis genes have been produced and analyzed over the last 6 years. In some cases these plants have been found to have elevated ABA concentrations, leading to altered stomatal behavior and increased seed dormancy. Genetic manipulation of ABA synthesis in photosynthetic tissues has been most effectively achieved through overexpression of the key rate-limiting biosynthetic enzyme 9-cis-epoxycarotenoid dioxygenase, and downregulation of the major catabolic enzyme ABA 8′-hydroxylase. However in non-photosynthetic tissue manipulation of ABA synthesis is a more complex task because of the limiting supply of xanthophyll precursors. The recent cloning of genes encoding enzymes controlling important pathways of ABA catabolism has been reviewed elsewhere, and so only information relevant to the regulation and manipulation of ABA synthesis, including supply of xanthophyll precursors, is discussed in this review.
102 citations
TL;DR: Recently, there have been breakthroughs on a number of fronts in abscisic acid biology research that have advanced the field significantly, including discovery of genes involved in ABA metabolism, along with progress in understanding of ABA signaling as mentioned in this paper.
Abstract: Recently there have been breakthroughs on a number of fronts in abscisic acid (ABA) biology research that have advanced the field significantly, including discovery of genes involved in ABA metabolism, along with progress in understanding of ABA signaling (Finkelstein and others 2002; Kushiro and others 2004; Lim and others 2005; Saito and others 2004). At the same time, the chemistry of ABA has advanced. New analytical methods have been developed for profiling ABA and catabolites (Ross and others 2004; Zaharia and others 2005). Novel bioactive catabolites have been discovered from feeding studies with deuterated ABA and catabolites (Zaharia and others 2004; Zhou and others 2004). This review covers recent advances and prospects in natural products chemistry, analysis of ABA catabolism, and applications of ABA analogs for biochemical studies and horticultural uses.
81 citations
TL;DR: It is shown that the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is known to stimulate hypocotyl elongation in the light, but this stimulation only occurs in cells of the apical half of the hypocrotyl, and ACC application can partially overcome light inhibition, whereas indole-3-acetic acid (IAA) cannot.
Abstract: During elongation of the Arabidopsis hypocotyl, each cell reacts to light and hormones in a time- and position-dependent manner. Growth in darkness results in the maximal length a wild-type cell can reach. Elongation starts at the base and proceeds in the acropetal direction. Cells in the upper half of the hypocotyl can become the longest of the whole organ. Light strongly inhibits cell elongation all along the hypocotyl, but proportionally more in the upper half. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) is known to stimulate hypocotyl elongation in the light. Here we show that this stimulation only occurs in cells of the apical half of the hypocotyl. Moreover, ACC application can partially overcome light inhibition, whereas indole-3-acetic acid (IAA) cannot. On low-nutrient medium (LNM) in the light, elongation is severely reduced as compared to growth on rich medium, and both ACC and IAA can stimulate elongation to the levels reached on a nutrient-rich medium. Furthermore, microtubule orientation was studied in vivo. During elongation in darkness, transverse and longitudinal patterns are clearly related with rates of elongation. In other conditions, except for the association of longitudinally orientated microtubules with growth arrest, microtubule orientation is merely an indicator of developmental age, not of elongation activity. A hypothesis on the relation between microtubules and elongation rate is discussed.
78 citations
TL;DR: The measurable events associated with ABA-induced stomatal closure in guard cells include, sequentially, the production of reactive oxygen species (ROS), increases in cytosolic free Ca2+ levels ([Ca2+]i), activation of anion channels, membrane potential depolarization, cytOSolic alkalinization, inhibition of K+ influx channels, and promotion of K+.
Abstract: The plant hormone abscisic acid (ABA) regulates a wide variety of plant physiological and developmental processes, particularly responses to environmental stress, such as drought. In response to water deficiency, plants redistribute foliar ABA and/or upregulate ABA synthesis in roots, leading to roughly a 30-fold increase in ABA concentration in the apoplast of stomatal guard cells. The elevated ABA triggers a chain of events in guard cells, causing stomatal closure and thus preventing water loss. Although the molecular nature of ABA receptor(s) remains unknown, considerable progress in the identification and characterization of its downstream signaling elements has been made by using combined physiological, biochemical, biophysical, molecular, and genetic approaches. The measurable events associated with ABA-induced stomatal closure in guard cells include, sequentially, the production of reactive oxygen species (ROS), increases in cytosolic free Ca2+ levels ([Ca2+]i), activation of anion channels, membrane potential depolarization, cytosolic alkalinization, inhibition of K+ influx channels, and promotion of K+ efflux channels. This review provides an overview of the cellular and molecular mechanisms underlying these ABA-evoked signaling events, with particular emphasis on how ABA triggers an “electronic circuitry” involving these ionic components.
57 citations
TL;DR: In this article, the ABA analog 8′ acetylene ABA methyl ester (PBI 429) was evaluated for its potential to alter the growth and moisture use of bedding plants during nursery production.
Abstract: The abscisic acid (ABA) analog 8′ acetylene ABA methyl ester (PBI 429) was evaluated for its potential to alter the growth and moisture use of bedding plants during nursery production. Treating seedlings with the ABA analog as a root-dip slowed moisture use and growth of tomato seedlings under greenhouse conditions. In marigolds, comparable ABA analog treatments had no effect on growth and limited effects on plant moisture use. To determine whether these differences in response to treatment with the ABA analog were associated with differences in absorption of the analog and/or its persistence, the ABA analog was applied either as a foliar spray or root-dip, and the resulting concentrations of the ABA analog were monitored over a 10-day interval in both the roots and the leaves. In both crops, the ABA analog was detected in both leaf and root tissues irrespective of the mode of application, suggesting systemic movement of the analog. Tissue concentrations of the ABA analog were consistently lower in the foliar treatment than in the root-dip. The uptake and the retention of the ABA analog over time was similar in leaves of the two test crops, but less of the ABA analog was absorbed and retained in the roots of marigold plants than in the tomatoes. This suggests that the observed differences in responses of these two plant species to application of ABA analogs may be related to differences in retention or accumulation of ABA in the roots rather than to differences in the total amount of ABA analog absorbed or its movement and retention in the plant system. Levels of endogenous ABA were not significantly altered by application of the ABA analog.
56 citations
TL;DR: In this paper, the rheological properties of enzymatically isolated plant cuticular membranes (CM) of mature leaves of Yucca aloifolia L., Hedera helix L., Nerium oleander L., and Lycopersicon esculentum Mill.
Abstract: The rheological properties of enzymatically isolated plant cuticular membranes (CM) of mature leaves of Yucca aloifolia L., Hedera helix L., Nerium oleander L., and Lycopersicon esculentum Mill. fruit were analyzed in a transient load-creep test. Cuticular membrane samples were tested dry and hydrated as submerged in distilled water. Apparent plastic extensibility turned out as delayed elastic extensibility, that is, CM showed visco-elastic behavior, if the system had sufficient time (up to 24 h) for relaxation. Both extensibility and the apparent plastic component increased in the hydrated state. In addition to hydration, different temperature regimes ranging from 7° to 30°C were established during testing to evaluate temperature sensitivity of cuticular rheology. Temperature-dependent changes of the rheological properties as small as 1°C could be detected. Extensibility was correlated with neither the thickness of the cuticles nor the specific structure of the cuticles as determined by scanning electron microscopy (SEM) and digital image analysis. For tomato fruit, no significant differences in extension behavior could be detected between CM and fruit skins, including the cell wall proper as analyzed in hydrated condition. The results demonstrate that the cuticle is a flexible biopolymer with rheological properties that can be dynamically modified by both hydration and temperature. The cuticle appears to have a pronounced impact on the overall mechanical behavior of the tomato fruit, implying a substantial contribution to the mechanical integrity of the whole organ. The described rheological properties of the tomato fruit CM are important features to accommodate growth processes without the loss of physiological integrity, but they may also help to understand fruit cracking as affected by hydration and temperature.
TL;DR: In this paper, the relationship between absicisic acid (ABA) and gibberellin (GA) changes in developing fruitlets from both Clementina and Okitsu trees subjected to changing water conditions was investigated.
Abstract: The relationship between absicisic acid (ABA) and gibberellin (GA) changes in developing fruitlets from both Clementina (Citrus clementina, Hort ex Tan) and Okitsu (Citrus unshiu, (Mak) Marc.) trees subjected to changing water conditions was investigated. The treatments consisted of a series of water stress, rainfall, and re-irrigation periods. To confirm the effectiveness of the imposed water changes, leaf water potential and soil moisture were measured. The data indicated that there were antagonistic changes between ABA and GA20, because in both species ABA increased and GA20 decreased during water stress, whereas re-hydration via either rainfall or irrigation reduced ABA but increased GA20. In addition, the data indicated that during water stress GA1 also decreased, whereas GA8 did not change. After re-hydration, however, levels of GA20 products, in general were rather dependent upon the hormonal levels induced in the previous water status. In conclusion, the results showed the occurrence of antagonistic changes between the levels of ABA and GA20 in developing citrus fruitlets subjected to changing water conditions. The data might suggest that gibberellin 20-oxidase is regulated by water stress in citrus fruits.
TL;DR: A significant role for cytokinin is indicated in the delay of senescence in broccoli by inhibiting ethylene perception and/or biosynthesis, thus regulating carbohydrate transport and metabolism, as well as senescences-associated gene expression.
Abstract: Broccoli (Brassica oleracea var. italica) deteriorates rapidly following harvest. The two plant hormones ethylene and cytokinin are known to act antagonistically on harvest-induced senescence in broccoli: ethylene by accelerating the process, and cytokinin by delaying it. To determine the level at which these hormones influenced senescence, we isolated and monitored the expression of genes normally associated with senescence in broccoli florets treated with exogenous 6-benzyl aminopurine (6-BAP), 1-aminocyclopropane-1-carboxylic acid (ACC), a combination of 6-BAP and ACC, and sucrose, in the five days following harvest. Exogenous 6-BAP caused both a reduction (BoACO) and an increase (BoACS) in ethylene biosynthetic gene expression. The expression of genes used as senescence markers, BoCP5 and BoMT1, was reduced, whereas BoCAB1 levels were maintained after harvest in response to exogenous 6-BAP. In addition, the expression of genes encoding sucrose transporters (BoSUC1 and BoSUC2) and carbohydrate metabolizing enzymes (BoINV1 and BoHK1) was also reduced upon 6-BAP feeding. Interestingly, the addition of ACC prevented the 6-BAP-induced increase in expression of BoACS, but 6-BAP negated the ACC-induced increase in expression of BoACO. The culmination of these results indicates a significant role for cytokinin in the delay of senescence. The implication that cytokinin regulates postharvest senescence in broccoli by inhibiting ethylene perception and/or biosynthesis, thus regulating carbohydrate transport and metabolism, as well as senescence-associated gene expression, is discussed and a model presented.
TL;DR: A high proportion of homologs to genes involved in somatic embryogenesis in the model system Daucus carota (carrot) were found in the Cyclamen EST collection, and a set of around 90 candidate genes that now can be tested in the wet lab for their influence on somatic embryo development in Cyclamen are disclosed.
Abstract: To learn more about the process of somatic embryogenesis in the economically important ornamental plant Cyclamen persicum, we initiated an expressed sequence tag (EST) project A normalized cDNA library was constructed from embryogenic cell material in different developmental stages, and clones were subsequently sequenced from the 5′ end A total of 2083 filtered EST with an average length of 499 bases were analyzed in this study and submitted to the international sequence databases By computational analyses, the Cyclamen transcripts were annotated and checked against plant genes previously described to be involved in somatic embryogenesis Approximately one third of those genes were covered by the Cyclamen EST analyzed in this study A high proportion of homologs to genes involved in somatic embryogenesis in the model system Daucus carota (carrot) were found in the Cyclamen EST collection Of special interest are transcripts encoding gibberellin oxidases and somatic embryogenesis receptor-like kinases (SERK), both of which were confirmed to be important for development of embryos from somatic carrot cells In addition, the set of candidate genes was expanded by using gene ontology (GO) annotations as well as by comparison with EST that were shown to be upregulated during Glycine max (soybean) somatic embryogenesis in a microarray approach Our computational biology approach disclosed a set of around 90 candidate genes that now can be tested in the wet lab for their influence on somatic embryogenesis in Cyclamen The annotated Cyclamen transcripts are available via http://wwwCyclamen-estde
TL;DR: The conversion of Z to DHZ by pea leaf enzyme was NADPH dependent and was significantly inhibited or completely suppressed in vitro by diethyldithiocarbamic acid (DIECA; 10 mM) and Relations of CKX and ZRED in the control of cytokinin levels in pea leaves with respect to their potential role in establishment and maintenance of cyt Kinostasis in plants are discussed.
Abstract: Cytokinin metabolism in plants is very complex. More than 20 cytokinins bearing isoprenoid and aromatic side chains were identified by high performance liquid chromatography-mass spectrometry (HPLC-MS) in pea (Pisum sativum L. cv. Gotik) leaves, indicating diverse metabolic conversions of primary products of cytokinin biosynthesis. To determine the potential involvement of two enzymes metabolizing cytokinins, cytokinin oxidase/dehydrogenase (CKX, EC 1.5.99.12) and zeatin reductase (ZRED, EC 1.3.1.69), in the control of endogenous cytokinin levels, their in vitro activities were investigated in relation to the uptake and metabolism of [2−3H]trans-zeatin ([2−3H]Z) in shoot explants of pea. Trans-zeatin 9-riboside, trans-zeatin 9-riboside-5′-monophosphate and cytokinin degradation products adenine and adenosine were detected as predominant [2−3H]Z metabolites during 2, 5, 8, and 24 h incubation. Increasing formation of adenine and adenosine indicated extensive degradation of [2−3H]Z by CKX. High CKX activity was confirmed in protein preparations from pea leaves, stems, and roots by in vitro assays. Inhibition of CKX by dithiothreitol (15 mM) in the enzyme assays revealed relatively high activity of ZRED catalyzing conversion of Z to dihydrozeatin (DHZ) and evidently competing for the same substrate cytokinin (Z) in protein preparations from pea leaves, but not from pea roots and stems. The conversion of Z to DHZ by pea leaf enzyme was NADPH dependent and was significantly inhibited or completely suppressed in vitro by diethyldithiocarbamic acid (DIECA; 10 mM). Relations of CKX and ZRED in the control of cytokinin levels in pea leaves with respect to their potential role in establishment and maintenance of cytokinin homeostasis in plants are discussed.
TL;DR: Cytokinins were capable of influencing either the synthesis or distribution of chlorophylls, but they did not alter cab and rbcS transcriptions in light-grown seedlings.
Abstract: Elevated cytokinins levels in vivo resulted in both enlarged and retarded growth phenotypes. Cytokinin levels were similar in both phenotypic groups. The ratio of the two phenotypes could be altered by changing the sucrose concentration in MS medium or the light intensity. Increased cytokinins in ipt:: GUS activated Arabidopsis induced the syntheses of anthocyanins and lignins, while light speeded up the anthocyanin accumulation. The endogenous increase in cytokinins and exogenous addition of sucrose in MS medium caused similar effects on the formation of anthocyanins and lignins in shoot, especially in the shoot apical meristem. Cytokinins induced CHS transcription in ipt:::GUS-activated Arabidopsis seedlings in the vegetative growth period; the transcription of CHS was low in ipt inactive plants and in wild-type Columbia. Cytokinins were capable of influencing either the synthesis or distribution of chlorophylls, but they did not alter cab and rbcS transcriptions in light-grown seedlings.
TL;DR: The results show that IAA homeostasis can be altered by heterologous overexpression of a conjugate-forming gene from maize and that the ZmIAGLU gene product is active in these plants.
Abstract: Overexpression of the IAGLU gene from maize (ZmIAAGLU) in Arabidopsis thaliana, under the control of the CaMV 35S promoter, inhibited root but not hypocotyl growth of seedlings in four different transgenic lines. Although hypocotyl growth of seedlings and inflorescence growth of mature plants was not affected, the leaves of mature plants were smaller and more curled as compared to wild-type and empty vector transformed plants. The rosette diameter in transgenic lines with higher ZmIAGLU expression was also smaller compared to the wild type. Free indole-3-acetic acid (IAA) levels in the transgenic plants were comparable to the wild type, even though a decrease in free IAA levels might be expected from overexpression of an IAA-conjugate–forming enzyme. IAA-glucose levels, however, were increased in transgenic lines compared to the wild type, indicating that the ZmIAGLU gene product is active in these plants. In addition, three different 35SZmIAGLU lines showed less inhibition of root growth when cultivated on increasing concentrations of IAA but not indole-3-butyric acid (IBA) and 2,4-dichlorophenoxyacetic acid (2,4-D). Feeding IAA to transgenic lines resulted in increased IAA-glucose synthesis, whereas the levels of IAA-aspartate and IAA-glutamine formed were reduced compared to the wild type. Our results show that IAA homeostasis can be altered by heterologous overexpression of a conjugate-forming gene from maize.
TL;DR: Transgenic plants of triticale cv.
Abstract: Transgenic plants of triticale cv. Wanad were obtained after transformation using three combinations of strain/vectors. Two of them were hypervirulent Agrobacterium tumefaciens strains (AGL1 and EHA101) with vectors containing bar under maize ubiquitin 1 promoter (pDM805), and both hpt under p35S and nptII under pnos (pGAH). The third one was a regular LBA4404 strain containing super-binary plasmid pTOK233 with selection genes the same as in pGAH. The efficiency of transformation was from 0 to 16% and it was dependent on the selection factor, auxin pretreatment, and the strain/vector combination. The highest number of transgenic plants was obtained after transformation with LBA4404(pTOK233) and kanamycin selection. Pretreatment of explants with picloram led to the highest number of plants obtained after transformation with both Agrobacterium/vector systems LBA4404(pTOK233) and EHA101(pGAH) and selected with kanamycin. Transgenic character of selected plants was examined by PCR using specific primers for bar, gus, nptII, and hpt and confirmed by Southern blot hybridization analysis. There was no GUS expression in T0 transgenic plants transformed with gus under p35S. However the GUS expression was detectable in the progeny of some lines. Only 30% of 46 transgenic lines showed Mendelian segregation of GUS expressing to GUS not expressing plants. In the remaining 70% the segregation was non-Mendelian and the rate was much lower than 3:1. Factors that might effect expression of transgenes in allohexaploid monocot species are discussed.
TL;DR: It is found that simultaneous application of IAA and GA3 to deseeded pericarps inhibited GA3-stimulated growth, and a growth regulatory role is proposed for 4-Cl-IAA through induction of GA biosynthesis and inhibition of ethylene action.
Abstract: This study explores the unique growth-regulatory roles of two naturally occurring auxins, indole-3-acetic acid (IAA) and 4-chloroindole-3-acetic acid (4-Cl-IAA), and their interactions with gibberellin (GA) during early pea (Pisum sativum L.) fruit development. We have previously shown that 4-Cl-IAA can replace the seed requirement in pea pericarp growth (length and fresh weight), whereas IAA had no effect or was inhibitory. When applied simultaneously, gibberellin (GA3 or GA1) and 4-Cl-IAA had a synergistic effect on pericarp growth. In the present study, we found that simultaneous application of IAA and GA3 to deseeded pericarps inhibited GA3-stimulated growth. The inhibitory effect of IAA on GA-stimulated growth was mimicked by treatment with ethephon (ethylene releasing agent), and the inhibitory effects of IAA and ethylene on GA-mediated growth were reversed by silver thiosulfate (STS), an ethylene action inhibitor. Although pretreatment with STS could retard senescence of IAA-treated pericarps, STS pretreatment did not lead to IAA-induced pericarp growth. Although 4-Cl-IAA stimulated growth whereas IAA was ineffective, both auxins induced similar levels of ethylene evolution. However, only 4-Cl-IAA-stimulated growth was insensitive to the effects of ethylene. Gibberellin treatment did not influence the amount of ethylene released from pericarps in the presence or absence of either auxin. We propose a growth regulatory role for 4-Cl-IAA through induction of GA biosynthesis and inhibition of ethylene action. Additionally, ethylene (IAA-induced or IAA-independent) may inhibit GA responses under physiological conditions that limit fruit growth.
TL;DR: A positive role for CKs in axillary bud growth is indicated and an early and large increase in iPAMP indicated rapid CK biosynthesis in rootless cuttings, suggesting that green parts, including the axillary buds, can synthesize CKs.
Abstract: Involvement of cytokinins (CKs) in axillary bud growth of miniature rose was studied. Variation in root formation and axillary bud growth was induced by two indole 3-butyric acid (IBA) pretreatments in two cutting sizes. At six physiological developmental stages around the onset of axillary bud growth, concentrations of CKs were determined in both root and axillary bud tissue by liquid chromatography combined with electrospray tandem mass spectrometry (LC-ESP-MS/MS). Chronological early onset of axillary bud growth occurred in long cuttings pretreated at low IBA concentration, whereas physiological early root formation was associated with long cuttings and high IBA concentration. The CKs zeatin (Z), isopentenyl adenine (iP), zeatin riboside (ZR), dihydrozeatin riboside (DHZR), isopentenyl adenosine (iPA), zeatin O-glucoside (ZOG), zeatin riboside O-glucoside (ZROG), zeatin riboside 5′-monophosphate (ZRMP), and isopentenyl adenosine 5′-monophosphate (iPAMP) were detected. Concentrations of CKs in axillary bud tissue far exceeded those in root tissue. Indole 3-butyric acid pretreatment influenced the concentration of CKs in axillary bud tissue more than did cutting size, whereas pretreatments only slightly affected CKs in root tissue. The dominant CKs found were iPAMP and ZR. An early and large increase in iPAMP indicated rapid CK biosynthesis in rootless cuttings, suggesting that green parts, including the axillary bud, can synthesize CKs. At the onset of axillary bud growth an increase in concentration of Z, ZR, ZRMP, ZOG, and ZROG was largely coincident with a decrease in iPAMP, iPA, iP, and DHZR. After the onset of axillary bud growth, CK content largely decreased. These results strongly indicate a positive role for CKs in axillary bud growth, and presumably ZRMP, ZR, and Z are active in miniature rose.
TL;DR: To better understand the role of the initial step in IAA esterification in the control of IAA levels, transgenic tomato plants were generated that either express maize IAGLU or have reduced levels of the enzyme IAA-glucose synthetase.
Abstract: Esterification of indole-3-acetic acid (IAA) is thought to be an important component in the homeostatic regulation of the levels of this phytohormone. To better understand the role of the initial step in IAA esterification in the control of IAA levels, transgenic tomato plants were generated that either express maize IAGLU or have reduced levels of the enzyme IAA-glucose synthetase. These plants were obtained by expressing maize IAGLU in either sense or antisense orientation using the CaMV35S promoter. The maize IAGLU probe hybridized to two transcripts (1.3 kb and 2.5 kb) in wild-type tomato vegetative tissue and green fruit. The sense and antisense transformants exhibited distinct phenotypic characteristics. Sense transformants showed an almost complete lack of root initiation and development. Antisense transgenic plants, on the other hand, had unusually well developed root systems at early stages in development, and the amount of the endogenous 75 kDa IAGLU protein was reduced. IAGLU antisense plants also had reduced levels of IAA-glucose and lower esterified IAA.
TL;DR: The enzyme kinetics and the biochemical characteristics of IAA-Ala hydrolase from one specific bacterium, Arthrobacter ilicis D-50, have been determined, and the enzyme has a unique substrate specificity for I AA-amino acid conjugates compared to a bacterial Iaa-Asp hydrol enzyme previously characterized.
Abstract: Indole-3-acetic acid (IAA)-amino acid amide conjugates have been found to be present in many plants, and they are proposed to function in the regulation of plant IAA metabolism in a variety of ways. IAA-amino acid conjugate hydrolase activities, and the genes that encode them, are therefore potentially important tools for modification of IAA metabolism, both for agronomic reasons as well as for determination of the mechanisms of IAA regulation. We have developed a simple and economical method to induce IAA-amino acid conjugate hydrolases in bacteria with N-acetyl-L-amino acids. Using this method, we identified four bacterial strains that can be induced to produce IAA-Ala hydrolases: Arthrobacter ureafaciens C-10, Arthrobacter ureafaciens C-50, Arthrobacter ilicis D-50, and Cellulomonas fimi D-100. The enzyme kinetics and the biochemical characteristics of IAA-Ala hydrolase from one specific bacterium, Arthrobacter ilicis D-50, have been determined. The enzyme has a unique substrate specificity for IAA-amino acid conjugates compared to a bacterial IAA-Asp hydrolase previously characterized.
TL;DR: Arabidopsis thaliana Δgai is unique in that it can be used both to prevent transgene outflow and to mitigate the flow should containment fail or should gene influx occur, a dual role for the gene, not previously reported.
Abstract: Mechanisms are needed to prevent gene flow from transgenic crops, and the later establishment of these transgenes in populations of other varieties, weeds, or wild relatives. Such prevention can be achieved by containing the transgene within a crop, and then mitigating the effects of the inherent leakage and unidirectionality of containment systems. Mitigation lowers the fitness of recipients below that of the wild-type so that transgenes cannot spread. Transplastomic and male-sterility systems suppress transgene outflow, but not the influx of pollen from relatives, requiring mitigation. The Arabidopsis thaliana Δgai (gibberellic acid–insensitive) gene, driven by its own promoter, induced male sterility in transgenic tobacco (Nicotiana tabacum), which is chemically reversible by kinetin applications. Female reproduction was not affected. Kinetin-treated sterile hemizygous and homozygous dwarf tobacco produced viable pollen, becoming self-fertile with copious viable seed, restoring the small amount of seed production needed for such a crop. Thus, Δgai, under its endogenous promoter, can be used as a containment mechanism to prevent transgene outflow. This application is in addition to the previously described highly effective role of Δgai as a dwarfing mitigator gene, which renders the rare transgenic tobacco hybrids unfit and unable to compete with the wild-type in the mixed cultures. Δgai is unique in that it can be used both to prevent transgene outflow and to mitigate the flow should containment fail or should gene influx occur, a dual role for the gene, not previously reported.
TL;DR: A spray of α-difluoromethylornithine (DFMO), an irreversible inhibitor of the putrescine biosynthetic inhibitor ornithine decarboxylase (ODC), markedly decreased the flowering and was reversed by application of Put alone or in combination with DFMO.
Abstract: Polyamine contents in xylem (root) and phloem (leaf) exudates in two diverse species of rose, viz. Rosa damascena Mill and Rosa bourboniana Desport, were analyzed before, during, and after flowering in the main flowering season, that is, April–May. Only free putrescine (Put) was detected in the xylem and phloem exudates at these time points, and it was high during the peak flowering period. In phloem, Put content was significantly higher in R. bourboniana than in R. damascena at all three stages; whereas in the xylem exudate it was relatively higher in R. damascena at the peak flowering period. A spray of α-difluoromethylornithine (DFMO), an irreversible inhibitor of the putrescine biosynthetic inhibitor ornithine decarboxylase (ODC), markedly decreased the flowering. This effect was reversed by application of Put alone or in combination with DFMO. The significance of this finding is discussed in light of polyamine translocation during flowering.
TL;DR: Multiple growth and developmental phenotypes reported for napp/gnarled/atnap, pirp/pirogi/atpir, and distorted3 mutants reveal that these WAVE proteins are also required for a wider variety of cellular functions in addition to regulating trichome cell growth, which has implications for the current view on cell morphogenesis in plants.
Abstract: Plants, as all other eukaryotic organisms, depend on a dynamic actin cytoskeleton for proper function and development. Actin dynamics is a complex process, regulated by a number of actin-binding proteins and large multiprotein complexes like ARP2/3 and WAVE. The ARP2/3 complex is recognized as a nucleator of actin filaments, and it generates a highly branched network of interlaced microfilaments. Results from multiple organisms show that ARP2/3 activity is regulated through multiple pathways. Recent results from plants point to a signaling pathway leading from the small GTPase RAC/ROP through a protein complex containing the ARP2/3-activating protein WAVE. This signaling pathway appears to be evolutionarily conserved. Support for this regulatory mechanism comes from studies of mutations in genes encoding subunits of the putative ARP2/3 complex and the WAVE complex in Arabidopsis. Several such mutants have defects of actin filament organization, leading to a conspicuous “distorted” trichome phenotype. Multiple growth and developmental phenotypes reported for napp/gnarled/atnap, pirp/pirogi/atpir, and distorted3 mutants reveal that these WAVE proteins are also required for a wider variety of cellular functions in addition to regulating trichome cell growth. These results have implications for the current view on cell morphogenesis in plants.
TL;DR: The effect of high temperature at the beginning of the forcing cycle on the structure of developing pollen grains of common lilac was investigated and high temperatures at the early forcing cycle resulted in the degeneration of most microspores.
Abstract: Forcing makes possible to induce plant flowering independently of the season. In lilac, high temperature is the factor that breaks deep dormancy. The deepest dormancy occurs between the end of October and the end of December. Depending on the depth of dormancy, the starting temperatures required for forcing are 37°C in November, 31°C in December, and 25°C in January–March. Under natural conditions, the temperature inducing the inflorescence bud breaking is 6°C, whereas 9°C and 13°C or more allow inflorescence elongation and flowering, respectively (Kronenberg, 1994). In the present work, the effect of high temperature at the beginning of the forcing cycle on the structure of developing pollen grains of common lilac was investigated. Pollen grains from the outdoor-grown (control) shrubs showed no signs of degeneration. They were spherical, three-colpate to colporoidate, and bicellular, and contained large numbers of lipid bodies. High temperatures at the early forcing cycle (November) resulted in the degeneration of most microspores. The first signs of degeneration (cytoplasm plasmolysis) were observed at the tetrad stage and in mature anthers; the microspores consisted only of the outer and inner sporopolenin layers.
TL;DR: Although both of the sHSPs act similarly as molecular chaperones, immunohistochemistry experiments support the hypothesis that the two have different cellular functions in the development of heat-induced cytoplasmic heat shock granules under elevated temperatures.
Abstract: Small heat shock proteins (sHSPs) are the most abundant stress proteins in plants. Usually not expressed under permissive conditions, they can accumulate to more than 2% of the total cellular protein content during heat stress. At present several points of evidence indicate that these proteins act as molecular chaperones by keeping partially denatured proteins in a folding-competent state. In plants sHSPs are encoded by a multigene family, which can be segregated into several classes according to their subcellular position and/or sequence homology. Curiously, two different classes appear in the cytoplasm. Their specific role during heat shock remains elusive. Here we present some evidence that both classes of sHSPs enhance recovery of reporter protein activity in the presence of HSP70. Applying peptide arrays prepared by SPOT synthesis and in situ analysis by confocal laser scanning microscopy, we could further show that the two classes of sHSP are attached to each other and are able to interact with non-native proteins both in vivo and in vitro. Although both of the sHSPs act similarly as molecular chaperones, immunohistochemistry experiments support the hypothesis that the two have different cellular functions in the development of heat-induced cytoplasmic heat shock granules under elevated temperatures.
TL;DR: The fact that the conformationally locked cyclopropanes exhibit growth-stimulating effects comparable to the flexible 6-alkylpurines and to BAP, supports the hypothesis that the orientation of the NH-CH2 bond in “the active conformation” of BAP is close to anti.
Abstract: 6-Alkynyl-, trans-6-alkenyl-, trans-6-cyclopropyl-and 6-alkylpurines structurally related to the cytokinin 6-benzylaminopurine (BAP) have been synthesized and examined with a radish cotyledon assay as plant growth stimulators. The growth stimulation obtained with the 6-alkylpurines trans-cyclopropylpurines was very close to that obtained with BAP, and the trans-styrylpurines were somewhat less effective. The fact that the conformationally locked cyclopropanes exhibit growth-stimulating effects comparable to the flexible 6-alkylpurines and to BAP, supports the hypothesis that the orientation of the NH-CH2 bond in “the active conformation” of BAP is close to anti, which means that the torsion angle C(6)-N(6)-CH2-C is approximately 180 degrees.
TL;DR: The progress toward understanding how ABA functions in higher plants is presented via reviews of selected topics and it is now accepted that ABA is produced by an ‘‘indirect’’ route in fungi.
Abstract: The name ‘‘abscisic acid’’ (ABA) was proposed in 1968 for the sesquiterpenoid hormone previously known as ‘‘dormin’’ or ‘‘abscisin II,’’ which had been isolated from several higher plants (Addicott and others 1968). In early studies its functions appeared mostly negative inasmuch as ABA treatments reduced growth and inhibited germination. However, it became clear that ABA was essential for normal growth and development, and we now know that ABA produces a huge range of both shortterm and long-term changes in cellular metabolism and processes. It has been estimated that 8–10% of Arabidopsis genes are ABA-responsive (Finkelstein and others 2002). As analytical methods improved, ABA was detected in algae, fungi, and liverworts in addition to higher plants (Hartung and Gimmler 1994). In this special issue, our progress toward understanding how ABA functions in higher plants is presented via reviews of selected topics. For many years the biosynthetic origin of ABA in higher plants was obscure. Although fungal pathways to ABA via farnesyl diphosphate were identified, these pathways could not be convincingly demonstrated in higher plants. Traditional tracer experiments to identify pathway intermediates were plagued by low incorporation rates. It became apparent that the biosynthetic route in fungi was quite different from that in higher plants. It is now accepted that ABA is produced by an ‘‘indirect’’
TL;DR: The 2005 Keystone Symposium on Plant Cell Signaling as mentioned in this paper brought together recent and exciting developments in plant cell signaling, and provided a platform to lay out and discuss the most modern methodologies and approaches that will govern how the next generation of scientists will propel plant biology into the post-genomic era.
Abstract: Scientists from around the world converged on Santa Fe, NM, February 1–6, 2005 (Figure 1), for a Keystone Symposium that brought together recent and exciting developments in plant cell signaling. The meeting also provided a platform to lay out and discuss the most modern methodologies and approaches that will govern how the next generation of scientists will propel plant biology into the ‘‘post-genomic’’ era. Although the remit of the conference covered Plant Cell Signaling, important developments and discoveries frequently spanned the biology of multiple species, and this was ably demonstrated in a number of talks that discussed experimental systems from different kingdoms. Such versatility was especially evident in the keynote address given by Michael Snyder (Yale University), who provided an overview of information made available by massive sequencing projects ( 250 fully sequenced genomes) and efficient use of this sequence information to reach the ultimate goal of understanding the function and regulation of each gene and protein. Within plant biology, it is clear that Arabidopsis thaliana largely remains the model system of choice, as its fully sequenced genome is being successfully exploited to fuel concepts within systems biology, large scale and high throughput screening. However, it is important to note that, in contrast to this, both novel methodology and exciting new developments were presented at this meeting using tobacco, maize, cotton, barley, tomato, and rice, illustrating continued diversity in experimental plant systems. On the technical side, advances in microscopy such as developments in Forster/fluorescence resonance energy transfer (FRET) techniques, and multi-mode fluorescence microscopy have allowed the maturation of practical methods not only to visualize fluorescently tagged proteins or subcellular compartments but also to analyze in vivo the dynamics of protein–protein interactions and intracellular trafficking in living cells. To this end, a specific workshop on FRET-related techniques and a session dedicated to development of single-cell techniques were also held at the meeting. Additionally, the power of the ‘‘in silico’’ biology became apparent with the introduction of a number of new Web-based tools allowing dissection of the ever-growing amount of data from highthroughput screens and analyses. In this report we focus on presentations that provided direction to the plant community and that summarized the most recent developments in the field. Authors are listed alphabetically and contributed equally. Received: 7 April 2005; accepted: 11 April 2005; Online publication: 28 July 2005 *Corresponding author; e-mail: j.p.taylor@unc.edu J Plant Growth Regul (2005) 24:46–54 DOI: 10.1007/s00344-005-0039-5