Showing papers on "Zeatin published in 2003"
TL;DR: It is concluded that hormone metabolism in thermodormant seeds is surprisingly active and is significantly different from that of germinating seeds.
Abstract: A highly selective and sensitive method for the simultaneous analysis of several plant hormones and their metabolites is described. The method combines high-performance liquid chromatography (HPLC) with positive and negative electrospray ionization-tandem mass spectrometry (ESI-MS/MS) to quantify a broad range of chemically and structurally diverse compounds. The addition of deuterium-labeled analogs for these compounds prior to sample extraction permits accurate quantification by multiple reaction monitoring (MRM). Endogenous levels of abscisic acid (ABA), abscisic acid glucose ester (ABA-GE), 7'-hydroxy-abscisic acid (7'-OH-ABA), phaseic acid (PA), dihydrophaseic acid (DPA), indole-3-acetic acid (IAA), indole-3-aspartate (IAAsp), zeatin (Z), zeatin riboside (ZR), isopentenyladenine (2iP), isopentenyladenosine (IPA), and gibberellins (GA)1, GA3, GA4, and GA7 were determined simultaneously in a single run. Detection limits ranged from 0.682 fmol for Z to 1.53 pmol for ABA. The method was applied to the analysis of plant hormones and hormonal metabolites associated with seed dormancy and germination in lettuce (Lactuca sativa L. cv. Grand Rapids), using extracts from only 50 to 100 mg DW of seed. Thermodormancy was induced by incubating seeds at 33 degrees C instead of 23 degrees C. Germinating seeds transiently accumulated high levels of ABA-GE. In contrast, thermodormant seeds transiently accumulated high levels of DPA after 7 days at 33 degrees C. GA1 and GA3 were detected during germination, and levels of GA1 increased during early post-germinative growth. After several days of incubation, thermodormant seeds exhibited a striking transient accumulation of IAA, which did not occur in seeds germinating at 23 degrees C. We conclude that hormone metabolism in thermodormant seeds is surprisingly active and is significantly different from that of germinating seeds.
324 citations
TL;DR: The results suggest that both ABA and cytokinins are involved in controlling plant senescence, and an enhanced carbon remobilization and accelerated grain filling rate are attributed to an elevated ABA level in wheat plants when subjected to water stress.
Abstract: This study investigated the possibility that abscisic acid (ABA) and cytokinins may mediate the effect of water deficit that enhances plant senescence and remobilization of pre-stored carbon reserves. Two high lodging-resistant wheat (Triticum aestivum L.) cultivars were field grown and treated with either a normal or high amount of nitrogen at heading. Well-watered (WW) and water-stressed (WS) treatments were imposed from 9 d post-anthesis until maturity. Chlorophyll (Chl) and photosynthetic rate (Pr) of the flag leaves declined faster in WS plants than in WW plants, indicating that the water deficit enhanced senescence. Water stress facilitated the reduction of non-structural carbohydrate in the stems and promoted the re-allocation of prefixed 14C from the stems to grains, shortened the grain filling period and increased the grain filling rate. Water stress substantially increased ABA but reduced zeatin (Z) + zeatin riboside (ZR) concentrations in the stems and leaves. ABA correlated significantly and negatively, whereas Z + ZR correlated positively, with Pr and Chl of the flag leaves. ABA but not Z + ZR, was positively and significantly correlated with remobilization of pre-stored carbon and grain filling rate. Exogenous ABA reduced Chl in the flag leaves, enhanced the remobilization, and increased grain filling rate. Spraying with kinetin had the opposite effect. The results suggest that both ABA and cytokinins are involved in controlling plant senescence, and an enhanced carbon remobilization and accelerated grain filling rate are attributed to an elevated ABA level in wheat plants when subjected to water stress.
215 citations
TL;DR: It was found that, in both the leaf tissues and leaf exudate, isopentenyladenine forms of cytokinins increased from 16 h after the start of the long day, and these cytokinin increases correlate well with the early events of floral transition.
Abstract: Understanding the complete picture of floral transition is still impaired by the fact that physiological studies mainly concern plant species whose genetics is poorly known, and vice versa. Arabidopsis thaliana has been successfully used to unravel signalling pathways by genetic and molecular approaches, but analyses are still required to determine the physiological signals involved in the control of floral transition. In this work, the putative role of cytokinins was investigated using vegetative plants of Arabidopsis (Columbia) induced to flower synchronously by a single 22 h long day. Cytokinins were analysed in leaf extracts, leaf phloem exudate and in the shoot apical meristem at different times during floral transition. It was found that, in both the leaf tissues and leaf exudate, isopentenyladenine forms of cytokinins increased from 16 h after the start of the long day. At 30 h, the shoot apical meristem of induced plants contained more isopentenyladenine and zeatin than vegetative controls. These cytokinin increases correlate well with the early events of floral transition.
188 citations
TL;DR: An efficient method to transform five cultivars of tomato (Lycopersicon esculentum), Micro-Tom, Red Cherry, Rubion, Piedmont, and E6203 is reported, which represents a simple, efficient and general means of transforming tomato.
162 citations
TL;DR: The results are a clear indication that O-glucosylation of cis-zeatin is a natural metabolic process in maize and serves as a precursor to the active trans-isomer or has any other unique function.
Abstract: trans-Zeatin is a major and ubiquitous cytokinin in higher plants. cis-Zeatin has traditionally been viewed as an adjunct with low activity and rare occurrence. Recent reports of cis-zeatin and its derivatives as the predominant cytokinin components in some plant tissues may call for a different perspective on cis-isomers. The existence of a maize (Zea mays) gene (cisZOG1) encoding an O-glucosyltransferase specific to cis-zeatin (R.C. Martin, M.C. Mok, J.E. Habben, D.W.S. Mok [2001] Proc Natl Acad Sci USA 98: 5922-5926) lends further support to this view. Results described here include the isolation of a second maize cisZOG gene, differential expression of cisZOG1 and cisZOG2, and identification of substantial amounts of cis-isomers in maize tissues. The open reading frame of cisZOG2 has 98.3% identity to cisZOG1 at the nucleotide level and 97.8% at the amino acid level. The upstream regions contain common and unique segments. The recombinant enzymes have similar properties, K(m) values of 46 and 96 microM, respectively, for cis-zeatin and a pH optimum of 7.5. Other cytokinins, including N(6)-(delta(2)-isopentenyl)adenine, trans-zeatin, benzyladenine, kinetin, and thidiazuron inhibited the reaction. Expression of cisZOG1 was high in maize roots and kernels, whereas cisZOG2 expression was high in roots but low in kernels. cis-Zeatin, cis-zeatin riboside, and their O-glucosides were detected in all maize tissues, with immature kernels containing very high levels of the O-glucoside of cis-zeatin riboside. The results are a clear indication that O-glucosylation of cis-zeatin is a natural metabolic process in maize. Whether cis-zeatin serves as a precursor to the active trans-isomer or has any other unique function remains to be demonstrated.
150 citations
TL;DR: This study is the first to demonstrate the potential of a polyamine-producing actinomycete to promote plant growth and the first published report of the production of polyamines by streptomycetes.
Abstract: Of seventy-five actinomycetes isolated from a bean rhizosphere in the United Arab Emirates, an isolate of Streptomyces griseoluteus (WT) was found to be capable of producing relatively high levels of putrescine on decarboxylase agar medium and to produce putrescine, spermidine and spermine in liquid decarboxylase medium. In the glasshouse, the application of the WT strain to soil amended with arginine (as a precursor for putrescine) significantly (P 0.05) differences between the levels of polyamines, endogenous PGRs, chlorophylls (a, b), and carotenoids between plants that were not exposed to either of the strain (control) and those grown in soil with the PNPM strain. Both WT and PNPM strains were incapable of producing in vitro detectable levels of PGRs, indole-acetic acid, indole-pyruvic acid, gibberellic acid, isopentenyl adenine and zeatin in the culture filtrates. This study is the first to demonstrate the potential of a polyamine-producing actinomycete to promote plant growth. In addition, it is also the first published report of the production of polyamines by streptomycete actinomycetes.
132 citations
TL;DR: Among the cytokinins tested, TDZ was found to be more effective cytokinin in the induction of PLBs than benzyladenine (BA) or zeatin, and callus-mediated PLB induction from cortical cells was found.
76 citations
TL;DR: It seems that endogenous iP concentration triggered the induction signal for an organogenic response in pineapple leaf bases, and the rise in iP content required the presence of BA and a-naphthaleneacetic acid (NAA) in the medium, suggesting that endogenous iPod production is regulated in response to these growth regulator uptakes.
Abstract: The in vitro culture of pineapple leaves on a shoot induction medium (SIM) results in the formation of protuberances and further development in shoots, and plantlets. The contents of endogenous indoleacetic acid (IAA) and five cytokinins (Cks), N6(2-isopentenyl)adenine (iP), N6(2-isopentenyl)adenosine (iPR), zeatin (Z), zeatin riboside (ZR) and N6-benzyladenine (BA), present in the basal portion of those leaves, were correlated to the organogenic response that occurs over 15 days of culture. The endogenous auxin/cytokinins ratio was lowest on the 3rd day, mainly due to a strong increase in the iP level. It seems that endogenous iP concentration triggered the induction signal for an organogenic response in pineapple leaf bases. The rise in iP content required the presence of BA and a-naphthaleneacetic acid (NAA) in the medium, suggesting that endogenous iP production is regulated in response to these growth regulator uptakes.
67 citations
TL;DR: Histological investigation showed that zeatin-induced meristemoids originated mainly from wounding tissues, and that TDZ induced a high level of mitotic division resulting in several proliferation zones nearby the epidermis and outer cortical tissues.
Abstract: The relative importance of explant, cytokinin type, carbon source and gelling agent for annatto organogenesis was studied The best organogenic response, including adventitious shoot number and elongation, was obtained when hypocotyl segments and rooted hypocotyls were cultured onto MS medium supplemented with 456 μM zeatin, 876 mM sucrose, and 28 g l−1 Phytagel® Adventitious shoots derived from hypocotyl segments were less frequent and more difficult to elongate than those derived from rooted hypocotyls Thidiazuron (TDZ) promoted a higher organogenic response in rooted hypocotyls, resembling a rosette-like structure, but impaired shoot elongation Histological investigation showed that zeatin-induced meristemoids originated mainly from wounding tissues, and that TDZ induced a high level of mitotic division resulting in several proliferation zones nearby the epidermis and outer cortical tissues Rhizogenesis efficiency (rooting frequency and root number) was greater at the highest indole-3-butyric acid (IBA) concentration (50 μM) employed, although calli occurred at the basal end of shoots Eighty percent of rooted plantlets survived after acclimatization This optimized regeneration protocol may enable further development of an efficient genetic transformation protocol for this species
61 citations
TL;DR: The relationship of assimilate supply to grape (Vitis vinifera L.) berry growth and development was studied with a seeded ('Kyoho') and a seedless ('Seedless Wuhehongʼ) cultivar as discussed by the authors.
Abstract: The relationship of assimilate supply to grape (Vitis vinifera L.) berry growth and development was studied with a seeded ('Kyohoʼ) and a seedless ('Seedless Wuhehongʼ) cultivar. A single shoot girdling between the second and third nodes below the basal cluster at the end of Stage I of berry growth shortened Stage II (the lag phase) of 'Kyohoʼ grape berries by 10 days, and eliminated Stage II in 'Seedless Wuhehongʼ grape berries. Double shoot girdling between the second and third nodes below the basal cluster and above the upper cluster, respectively, at the same time at the end of Stage I, advanced Stage II by 3 days in both cultivars. Normal accumulation of dry weight in the 'Kyohoʼ grape berry is in a double sigmoidal pattern, but it became a single sigmoidal pattern in response to a single basal girdling. The highest percent moisture in berries was at 20 days after full bloom. Rapid changes in berry pectin substances lagged behind those of soluble solids and titratable acidity, and behind the onset of berry softening at veraison in 'Kyohoʼ, but not in 'Seedless Wuhehongʼ, for which the three processes were con cur rent. It is suggested that the slow growth of the berries during Stage II is a result of a decrease in the rate of water accumulation on a whole berry basis and a decrease in accumulation of dry matter in the skin and fl esh (pericarp) due to assimilate com pe ti tion within grapevines and within berries. The relationships between levels of endogenous hormones (IAA, GA3, zeatin, zeatin riboside, and ABA) and berry growth were also studied with 'Kyohoʼ grapes. The results showed that the slow growth of grape berries during Stage II was associated with assimilate com pe ti tion between the skin-fl esh (pericarp) and seeds, and with peak shifts of concentrations of IAA, GA3, zeatin and zeatin riboside. Changes in ABA levels were closely associated with ripening and senescence during late Stage III. has been paid to the ripening process with the suggestion that the auxin-ABA relationship might be involved in the hormonal regulation of veraison and ripening of grape berries.
53 citations
TL;DR: Silicon nutrition in symbiotic cowpea promotes an increase in mechanical strength of stems, which bear the entire weight of shoots, and peduncles, which, in turn, support weighty reproductive structures including developing pods and seeds.
Abstract: Application of metasilicic acid (0, 0.04, 0.08, 0.20, 0.40 or 0.80 g L-1) to hydroponically-grown, Bradyrhizobium-infected cowpea [Vigna unguiculata (L.) Walp.] plants showed an increased assimilation of silicon into roots and shoots, which triggered a significant (P<0.05) promotion of root growth, but not shoot growth. Root : shoot ratio therefore, increased markedly (P<0.05) with higher metasilicate application. Mechanical strength of stems and peduncles also increased significantly (P<0.05) with silicon nutrition compared with control plants receiving no metasilicate. But the mechanical strength of roots was not affected. Radioimmunoassay of lateral roots, free of nodules, from plants fed metasilicate revealed markedly (P<0.05) increased concentrations of endogenous ABA, a hormonal signal that stimulates root growth. In contrast, a decreasing concentration of the cytokinin zeatin ribose was obtained with increasing metasilicate supply. These data show that silicon nutrition in symbiotic cowpea promotes an increase in mechanical strength of stems, which bear the entire weight of shoots, and peduncles, which, in turn, support weighty reproductive structures including developing pods and seeds. The increased concentration of ABA in roots as a result of improved silicon nutrition suggests that this element might be an elicitor of ABA biosynthesis and / or its accumulation, which then affected lateral root growth in this study.
TL;DR: Modelling and measuring of the dynamics of endogenous cytokinins in tobacco plants grown on media supplemented with isopentenyl adenine, zeatin and dihydrozeatin riboside and a simple mathematical model of cytokinin metabolism in developing seedlings found a close match between measured and simulated data.
TL;DR: Different media were assayed for Olea europaea L. maderensis Lowe micropropagation and up to now no morphological changes were observed among the regenerated in vitro plants.
TL;DR: The effects of some endogenous hormones on the control of axillary bud development of pineapple Ananas comosus (L.) Merr.
TL;DR: While researchers had long speculated that a hormone which affected abscission, dormancy, and stress reduction existed, it was not until the 1960s when gas chromatography was used to quantify endogenous ethylene that the significance of ethylene was recognized and acknowledged as an endogenous hormone.
Abstract: DNA breakdown (Miller et al., 1955). Kinetin was significantly more active than adenine in the tobacco tissue culture bioassay. The use of the plant cell culture bioassay was a key to the eventual isolation of zeatin from corn by Letham (1963). ETHYLENE. The growth regulating properties of ethylene were first recognized by the Russian scientist Nejebulov in 1901 (Beyer et al., 1984). His experiments showed that illuminating gas could cause leaf abscission and epinasty. The fruit physiologist Crocker developed the Alaskan pea bioassay that used the triple response of shortening and thickening of the hypocotyl, agravitropic growth, and maintained hypocotyl hook (Reid and Howell, 1995) to assess ethylene levels. He was the first to suggest that ethylene was an endogenous plant hormone. However, few scientist at the time agreed with Crocker since it was difficult to visualize that a gas could act as an endogenous regulating substance. It was not until the 1960s when gas chromatography was used to quantify endogenous ethylene that the significance of ethylene was recognized and acknowledged as an endogenous hormone. ABSCISIC ACID.While researchers had long speculated that a hormone which affected abscission, dormancy, and stress reduction existed, it was not until the 1950s that work on the isolation and identification of this compound began. In 1953 Bennet-Clark and Kefford discovered an acid fraction of plant extracts that was a potent growth inhibitor. In 1955 Osborne reported on the diffusion of a senescence factor from older leaves that could speed the abscission of bean petioles. By 1963, Addicott s group studying cotton fruit abscission in California had identified and characterized abscisin II. At the same time, Wareing s group in Wales identified the dormin as a compound that promoted dormancy in woody plants. In 1968, these groups formally redesignated abscisin II and dormin as abscisic acid (Milborrow, 1984).
TL;DR: The present study reports the analyses of both isoprenoid and aromatic cytokinins in the coconut palm by combined high performance liquid chromatography and group specific enzyme immunoassays (HPLC-ELISA).
Abstract: The present study reports the analyses of both isoprenoid and aromatic cytokinins in the coconut palm by combined high performance liquid chromatography and group specific enzyme immunoassays (HPLC-ELISA). The results showed that the isoprenoid cytokinins were several fold more abundant than the aromatic cytokinins in each of the plant parts analysed: immature inflorescence, shoot apical meristem (SAM), spear leaf and embryo. Within the isoprenoid cytokinins, the most abundant ones by type were the zeatin- (Z-), the isopentenyladenine- (iP-) and the dihydrozeatin- (DHZ-) type in decreasing order for most plant parts studied, and individually, zeatin riboside (ZR) or zeatin riboside-5′-monophosphate (ZR5′P) depending on the part. In the case of the iP-type cytokinins, the results showed that its 9-glucoside was the most abundant one in most parts. The isoprenoid cytokinin profiles in coconut showed a predominant pattern of 9-conjugation as a major metabolism route for these cytokinins. Analyses also showed the occurrence of the aromatic cytokinin 6-benzylaminopurine (BAP) and its riboside (BAPR), 9-glucoside (BAP9G), and nucleotide (BAPR5′P). Their presence in coconut palm was unequivocally identified after permethylation by gas chromatography-mass spectrometry. They were more concentrated in the embryo and in the immature inflorescence than in the other two parts studied, however their concentration in each part was several times lower than that of isoprenoid cytokinins. All four were detected in each of the parts studied. The most abundant ones were BAPR and BAP9G in immature inflorescence; and BAPR in all of the other parts. When all cytokinins analysed are considered, differences between the plant parts studied were found. The zygotic embryos showed the highest content, double that in immature inflorescence, and five times more that in spear leaf and SAM. These differences are even greater when individual cytokinins are compared.
TL;DR: A comparison of the cytokinin pattern in transgenic and wild-type plants indicates that these specific metabolites accumulate as a consequence of enhanced cytokinIn biosynthesis, and are probably involved in the homeostatic mechanisms that control endogenous cytokin in plants.
Abstract: Two novel cytokinin metabolites were identified in transgenic Arabidopsis thaliana (L.) Heynh. plants containing the bacterial IPT gene under the transcriptional control of a heat-regulated promoter. After cyclic heat-shock treatment, the endogenous cytokinin concentrations were elevated up to 100-fold compared to the wild-type plants. More then 20 different cytokinin metabolites were found, with zeatin-type cytokinins being the most abundant. The metabolic inactivation of these compounds occurred predominantly through N-glucosylation. No significant accumulation of isopentenyladenine-type cytokinins, and only a small increase in dihydrozeatin metabolites, was observed. Subsequent studies of the abundant, unidentified conjugates revealed the presence of zeatin and dihydrozeatin diglucoside conjugates. Structural analysis, utilizing electrospray-liquid tandem mass spectrometry, identified these as a zeatin-O-glucoside-9-glucoside and dihydrozeatin-O-glucoside-9-glucoside, respectively. A third unknown metabolite, was tentatively identified as a phosphorylated form of zeatin-9-glucoside. The biological activity of these compounds in three cytokinin bioassays was low. A comparison of the cytokinin pattern in transgenic and wild-type plants indicates that these specific metabolites accumulate as a consequence of enhanced cytokinin biosynthesis, and are probably involved in the homeostatic mechanisms that control endogenous cytokinin levels.
TL;DR: Callus and bud regeneration frequency, callus growth, and number of buds and shoots per regenerating explant depended not only on the specific segment of the hypocotyl, but also on parental genotype.
Abstract: An improved protocol for shoot regeneration from hypocotyl segments of seedlings from open-pollinated seeds of lingonberry (Vaccinium vitis-idaea L.) cultivars, ‘Ida’, ‘Splendor’, and ‘Erntesegen’, and a native clone from Newfoundland was developed. The effect of thidiazuron (TDZ) on adventitious bud and shoot formation from apical, central, and basal segments of the hypocotyl was tested. Highly regenerative callus was obtained from hypocotyl segments on modified Murashige and Skoog (MMS) medium containing 5–10 μM TDZ. A maximum of 10 buds and 12 shoots per apical segment for seedlings of cultivar ‘Ida’ regenerated on MMS containing 10 μM TDZ. Callus and bud regeneration frequency, callus growth, and number of buds and shoots per regenerating explant depended not only on the specific segment of the hypocotyl, but also on parental genotype. Inhibition of shoot elongation by TDZ was overcome by transferring shoot cultures to a shoot proliferation medium containing 1–2 μM zeatin. The optimal concentration of sucrose for shoot elongation was 20 gl−1. Shoots were rooted ex vitro on a 2 peat: 1 perlite (v/v) medium after dipping in 0.8% indole-3-butyric acid, and rooted plants acclimatized readily under greenhouse conditions.
TL;DR: It can be inferred that xylem sap CKs represent one source of active CKs appearing in lateral buds after shoot decapitation, which may be a passive signalling mechanism central to initiation of lateral bud release in chickpea seedlings.
Abstract: Although cytokinins (CKs) are widely thought to have a role in promoting shoot branching, there is little data supporting a causative or even a correlative relationship between endogenous CKs and timing of bud outgrowth. We previously showed that lateral bud CK content increased rapidly following shoot decapitation. However, it is not known whether roots are the source of this CK. Here, we have used shoot decapitation to instantaneously induce lateral bud release in chickpea seedlings. This treatment rapidly alters rate and direction of solvent and solute (including CK) trafficking, which may be a passive signalling mechanism central to initiation of lateral bud release. To evaluate changes in xylem transport, intact and decapitated plants were infiltrated with [H-3]zeatin riboside ([H-3]ZR), a water-soluble blue dye or [H-3]H2O by injection into the hypocotyl. All three tracers were recovered in virtually all parts of the shoot within I h of injection. In intact plants, solute accumulation in the lateral bud at node 1 was significantly less than in the adjacent stipule and nodal tissue. In decapitated plants, accumulation of [H-3]ZR and of blue dye in the same bud position was increased 3- to 10-fold relative to intact plants, whereas content of [H-3]H2O was greatly reduced indicating an increased solvent throughput. The stipule and cut stem, predicted to have high evapotranspiration rates, also showed increased solute content accompanied by enhanced depletion of [H-3]H2O. To assess whether metabolism modifies quantities of active CK reaching the buds, we followed the metabolic fate of [H-3]ZR injected at physiological concentrations. Within 1 h, 80-95% of [H-3]ZR was converted to other active CKs (mainly zeatin riboside-5'phosphate (ZRMP) and zeatin (Z)), other significant, but unconfirmed metabolites some of which may be active (O-acetylZR, O-acetylZRMP and a compound correlated with sites of high CK-concentrations) and inactive catabolites (adenosine, adenine, 5'AMP and water). Despite rapid metabolic degradation, the total active label, which was indicative of CK concentration in buds, increased rapidly following decapitation. It can be inferred that xylem sap CKs represent one source of active CKs appearing in lateral buds after shoot decapitation.
TL;DR: The effect of root inoculation by mycorrhizal fungi (Glomus mosseae) on zeatin/zeatin riboside (Z/ZR),isopentenyladenine/isopENTenyladenosine (iAde/iAdo) and water relations in grapevine (Vitis vinifera L. ‘Cabernet Sauvignon’) was studied.
Abstract: SummaryThe effect of root inoculation by mycorrhizal fungi (Glomus mosseae) on zeatin/zeatin riboside (Z/ZR),isopentenyladenine/isopentenyladenosine (iAde/iAdo) and water relations in grapevine (Vitis vinifera L. ‘Cabernet Sauvignon’) was studied. Two soil moisture treatments (well-watered or stressed) and mycorrhizal colonization (present or absent) were applied to plants in pots grafted onto eight grapevine rootstocks (110 Richter, 41BMgt, 1103 Paulsen, 5BB Kober, 44–53 Malegue, 140 Ruggeri and 101–14Mgt). Cytokinin production of mycorrhizal (M) plants was greater than that of non-mycorrhizal (NM) ones. In both well-watered and stressed plants, concentrations of Z/ ZR in shoot tips ranged from 2.75 to 87.7 ng g–1 dry wt., being higher than those of iAde/iAdo in most cases, ranging from 4.01 to 25.2 ng g–1 dry wt. Significantly lower concentrations for both types of cytokinins were found in stressed plants. M stressed vines had higher predawn leaf water potential, stomatal conductance and CO2 assimilatio...
TL;DR: The enhancement of starch synthesis and accumulation in the pith and the retardation of these processes in the cortex followed the changes in the ABA content providing indirect support to the previously made observation that the exogenous ABA promoted starch biosynthesis.
Abstract: The contents of ABA, IAA, and cytokinins (zeatin + zeatin riboside) were determined in the cortex and pith of medium-sized (25 g) and large (120 g) tubers of potato (Solanum tuberosum L., cv. Malakhit) at the end of the flowering phase (48 days after sprouting) and related to plant growth (cell division and enlargement) and starch biosynthesis and deposition. The patterns of phytohormone distribution were different in the cortex and pith. In the latter, with most cells at the enlargement phase, the IAA content increased, as well as the ratios IAA/ABA and IAA/cytokinins. In the cortex dominated by the dividing cells, the ABA content declined, and the ratio cytokinins/ABA exceeded that in the pith. The enhancement of starch synthesis and accumulation in the pith and the retardation of these processes in the cortex followed the changes in the ABA content providing indirect support to the previously made observation that the exogenous ABA promoted starch biosynthesis. The data obtained are discussed in the context of the hormonal control of carbohydrate metabolism and starch deposition in growing tubers.
TL;DR: A new reliable protocol for the induction of adventitious shoots and plant regenertion from cotyledon-derived callus of Acacia sinuata has been developed and it was revealed that the regenerated shoots originated from the callus.
Abstract: A new reliable protocol for the induction of adventitious shoots and plant regenertion from cotyledon-derived callus of Acacia sinuata has been developed. Calluses were induced from cotyledon explants on Murashige and Skoog (MS) medium containing 3% sucrose, 0.8% agar or 0.15% phytagel, 8.1 μM α-naphthaleneacetic acid, and 2.2 μM 6-benzylaminopurine (BA). High-frequency regeneration of adventitious buds from callus was achieved when cultured on half-strength MS medium supplemented with 10% coconut water, 13.3 μM BA, and 2.5 μM zeatin. Histological studies revealed that the regenerated shoots originated from the callus. Among the various carbohydrates tested, sucrose at 87.6 mM was optimum for shoot-bud induction. Addition of 1.7 μM gibberellic acid along with 4.4 μM favored shoot elongation. In vitro-raised shoots produced prominent roots when transferred to half-strength MS medium supplemented with 7.4 μM indole-3-butyric acid. Rooted plants, thus developed, were hardened and successfully established in soil (45%). This protocol yielded an average of 40 plantlets per cotyledon explant over a period of 3 mo.
TL;DR: Cation exchange resin, paper chromatography and High Performance Liquid Chromatography were used to purify the plant and culture medium extracts and cytokinin-like activity was detected using the soybean callus bioassay in all the plant extracts.
TL;DR: A new enzymatic reaction method for the preparation of the radioisotope-labeled cytokinins isopentenyladenine (iP), trans-zeatin (tZ), and their ribosides that affords a much higher yield of the labeled products than the chemical reaction methods previously used.
Abstract: We describe a new enzymatic reaction method for the preparation of the radioisotope-labeled cytokinins isopentenyladenine (iP), trans-zeatin (tZ), and their ribosides. The method is based on the three enzyme activities of an adenylate isopentenyltransferase (IPT; EC 2.5.1.27) from Arabidopsis thaliana, an alkaline phosphatase (EC 3.1.3.1) from calf intestine, and a purine-nucleoside phosphorylase (EC 2.4.2.1) from Escherichia coli. The A. thaliana IPT, AtIPT7, utilized both dimethylallyldiphosphate and 4-hydroxy-3-methyl-2-(E)-butenyl diphosphate as isoprenoid donors. The dual specificity of the substrates enabled us to produce iP-type and tZ-type cytokinins separately in the same system simply by switching the substrates. Our method affords a much higher yield of the labeled products than the chemical reaction methods previously used. These labeled compounds will be useful tools for cytokinin research, such as receptor–ligand assays and cell metabolism studies.
TL;DR: Cotyledons excised from seedlings of Cajanus cajan (pigeonpea) were grown on media containing cytokinins and thidiazuron, which induced divisions in the epidermal and sub-epidermal cell layers leading to the formation of primary protrusions on the surface and the development of foci of high meristematic activity.
Abstract: Cotyledons excised from seedlings of Cajanus cajan (pigeonpea) were grown on media containing cytokinins (6-benzyladenine, zeatin, and zeatin riboside) and an allied compound, thidiazuron. With the exception of zeatin riboside, initial response in terms of induction of organized structures was very high. However, subsequent regeneration of shoots from cotyledon explants was very poor. Anatomical studies on the regenerating explants were undertaken to study the pattern of morphogenesis. Cytokinins and thidiazuron induced divisions in the epidermal and sub-epidermal cell layers leading to the formation of primary protrusions on the surface. This was followed by the development of foci of high meristematic activity either on the surface or within the primary protrusions. These foci differentiated into embryo-like structures or shoot meristem-like structures. Mostly aberrant shoots, with poorly developed apical meristems, regenerated from these structures.
TL;DR: A clear relationship between the endogenous content of phytohormones and the growth characteristic of kiwifruit microplants could be confirmed and these ratios at the end of the multiplication phase could be used as growth indicators of A. deliciosa explants behaviour under ex vitro conditions.
TL;DR: The effects of the antioxidant Ambiol and 2-chlorethylphosphonic acid (2-CEPA) on individual concentrations and concentration ratios of phytohormones, photosynthesis and photophosphorylation rates, sucrose and starch content in tubers, and plant productivity were studied in potato.
Abstract: The effects of the antioxidant Ambiol and 2-chlorethylphosphonic acid (2-CEPA) on individual concentrations and concentration ratios of phytohormones, photosynthesis and photophosphorylation rates, sucrose and starch content in tubers, and plant productivity were studied in potato (Solanum tuberosum L). Ambiol increased the ratio of indoleacetic acid (IAA) to abscisic acid (ABA), IAA/ABA, and that of zeatin (Z) and zeatin riboside (ZR) to ABA, (Z + ZR)/ABA. These effects were underlain by an increase in the content of auxins and cytokinins and a decrease in ABA. Unlike Ambiol, 2-CEPA increased the level of ABA, the effect being the most pronounced in the tubers. Ambiol increased the rates of photosynthesis and noncyclic photophosphorylation in chloroplasts isolated from potato leaves. The relation of this phenomenon to auxin and cytokinin accumulation, Ambiol- and 2-CEPA-induced changes in the hormonal balance of potato tubers, carbon metabolism, and plant productivity is discussed.
TL;DR: The presented results show for the first time a plant adenosine kinase affinity‐purified to homogeneity that was identified by primary structure analysis.
TL;DR: Results in terminal buds showed increasing amounts of indole-3-acetic acid (IAA) the more reinvigorated the plant material was, whereas an enhancement in total cytokinins levels was observed in axillary buds, corroborating previous findings in which the ratio of isopentenyladenine-type to zeatin-type Cks was reported as an ageing and vigour index.
TL;DR: Recombinant mung bean CSBP has been overexpressed in Escherichia coli and crystallized in complex with zeatin, a natural plant growth hormone, which binds with very high affinity to cytokinin-specific binding proteins (CSBPs).
Abstract: Cytokinins, or plant growth hormones, bind with very high affinity to cytokinin-specific binding proteins (CSBPs). Recombinant mung bean CSBP has been overexpressed in Escherichia coli and crystallized in complex with zeatin, a natural plant growth hormone. The crystals belong to the hexagonal system, space group P62 or P64, with unit-cell parameters a = 113.62, c = 86.85 A, contain two to five copies of the protein in the asymmetric unit and diffract X-rays to 1.25 A resolution.