Showing papers on "Shoot published in 1998"

The Role of EDTA in Lead Transport and Accumulation by Indian Mustard

Abstract: Indian mustard (Brassica juncea) plants exposed to Pb and EDTA in hydroponic solution were able to accumulate up to 55 mmol kg−1 Pb in dry shoot tissue (1.1% [w/w]). This represents a 75-fold concentration of Pb in shoot tissue over that in solution. A threshold concentration of EDTA (0.25 mm) was found to be required to stimulate this dramatic accumulation of both Pb and EDTA in shoots. Below this threshold concentration, EDTA also accumulated in shoots but at a reduced rate. Direct measurement of a complex of Pb and EDTA (Pb-EDTA) in xylem exudate of Indian mustard confirmed that the majority of Pb in these plants is transported in coordination with EDTA. The accumulation of EDTA in shoot tissue was also observed to be directly correlated with the accumulation of Pb. Exposure of Indian mustard to high concentrations of Pb and EDTA caused reductions in both the transpiration rate and the shoot water content. The onset of these symptoms was correlated with the presence of free protonated EDTA (H-EDTA) in the hydroponic solution, suggesting that free H-EDTA is more phytotoxic than Pb-EDTA. These studies clearly demonstrate that coordination of Pb transport by EDTA enhances the mobility within the plants of this otherwise insoluble metal ion, allowing plants to accumulate high concentrations of Pb in shoots. The finding that both H-EDTA and Pb-EDTA are mobile within plants also has important implications for the use of metal chelates in plant nutritional research.

A common mechanism controls the life cycle and architecture of plants

Abstract: The overall aerial architecture of flowering plants depends on a group of meristematic cells in the shoot apex. We demonstrate that the Arabidopsis TERMINAL FLOWER 1 gene has a unified effect on the rate of progression of the shoot apex through different developmental phases. In transgenic Arabidopsis plants which ectopically express TERMINAL FLOWER 1, both the vegetative and reproductive phases are greatly extended. As a consequence, these plants exhibit dramatic changes in their overall morphology, producing an enlarged vegetative rosette of leaves, followed by a highly branched inflorescence which eventually forms normal flowers. Activity of the floral meristem identity genes LEAFY and APETALA 1 is not directly inhibited by TERMINAL FLOWER 1, but their upregulation is markedly delayed compared to wild-type controls. These phenotypic and molecular effects complement those observed in the tfl1 mutant, where all phases are shortened. The results suggest that TERMINAL FLOWER 1 participates in a common mechanism underlying major shoot apical phase transitions, rather than there being unrelated mechanisms which regulate each specific transition during the life cycle.

Genetic evidence that the endodermis is essential for shoot gravitropism in Arabidopsis thaliana

Abstract: Shoots of higher plants exhibit negative gravitropism. However, little is known about the mechanism or site of gravity perception in shoots. We have identified two loci that are essential for normal shoot gravitropism in Arabidopsis thaliana. Genetic analysis demonstrated that the shoot gravitropism mutants sgr1 and sgr7 are allelic to the radial pattern mutants, scr and shr, respectively. Characterization of the aerial phenotype of these mutants revealed that the primary defect is the absence of a normal endodermis in hypocotyls and influorescence stems. This indicates that the endodermis is essential for shoot gravitropism and strongly suggests that this cell layer functions as the gravity-sensing cell layer in dicotyledonous plant shoots. These results also demonstrate that, in addition to their previously characterized role in root radial patterning, SCR and SHR regulate the radial organization of the shoot axial organs in Arabidopsis.

Altered Zn Compartmentation in the Root Symplasm and Stimulated Zn Absorption into the Leaf as Mechanisms Involved in Zn Hyperaccumulation in Thlaspi caerulescens

Abstract: Phytoextraction is an emerging technology that involves the use of vascular plants to remediate soils contaminated with heavy metals and/or radionuclides (Nanda Kumar et al., 1995). This approach is based on the ability of higher plants to absorb contaminants from the soil and translocate them to their shoots. The identification of several metal-hyperaccumulator plant species (Baker and Brooks, 1989; Baker et al., 1998) demonstrates that the genetic potential exists for successful phytoremediation of contaminated soils. One of the best-known metal hyperaccumulators is Thlaspi caerulescens JC Chaney, 1993; Baker et al., 1994; Brown et al., 1994, 1995a, 1995b). Recently, Brown et al. (1995b) reported that from a hydroponic medium, T. caerulescens accumulated more than 25,000 μg Zn g−1 before symptoms of Zn toxicity (i.e. shoot biomass reduction) occurred. Although T. caerulescens has the ability to transfer high levels of Zn and other metals from the soil into the shoot, the use of this species for commercial remediation of contaminated soils is severely limited by its small size and slow growth (Ebbs et al., 1997). The transfer of Zn-hyperaccumulating properties from T. caerulescens into a high-biomass-producing plant has been suggested as a potential avenue for making phytoremediation a commercial technology (Brown et al., 1995a). Progress in this area, however, is hindered by a lack of understanding of the basic physiological mechanisms involved in Zn uptake into roots and translocation to aboveground tissues. In a previous study we reported that Zn influx into root symplasm of Zn-hyperaccumulator and -nonaccumulator species of Thlaspi was mediated by a saturable component with similar affinities for Zn (Lasat et al., 1996). However, the maximum capacity for Zn transport across the plasma membrane into the cytosol was 4.5-fold greater in the Zn-accumulator T. caerulescens compared with the Zn-nonaccumulator Thlaspi arvense L. These results indicate that one characteristic of T. caerulescens is a greater capacity for Zn absorption from soil solution into root cells. Enhanced Zn uptake into the root symplasm of T. caerulescens was also associated with a greater capacity for Zn translocation to the shoot (Lasat et al., 1996). For example, after 96 h of exposure to a 65Zn-labeled uptake solution, 10-fold more 65Zn accumulated in the shoots of T. caerulescens compared with T. arvense, and 1.2-fold more 65Zn accumulated in the roots of T. arvense compared with T. caerulescens. These results suggest that in addition to Zn entry into the root symplasm, other Zn-transport sites are altered in T. caerulescens, contributing to the dramatic increase in Zn translocation and storage in the shoot. We used hydroponically grown T. arvense and T. caerulescens seedlings to investigate several mechanisms possibly involved in Zn hyperaccumulation: (a) stimulated Zn transport from the root symplasm into the xylem sap; (b) xylem accumulation of low-Mr organic ligands possibly involved in Zn complexation and transport to the shoot; and (c) enhanced Zn transport into leaf cells.

Biofumigation potential of brassicas. I. Variation in glucosinolate profiles of diverse field-grown brassicas

Abstract: Biofumigation refers to the suppression of soil-borne pests and pathogens by biocidal compounds released in soil when glucosinolates (GSL) in Brassica green manure or rotation crops are hydrolysed. We investigated the potential to enhance biofumigation by considering the variation in GSL production in the roots and shoots of 76 entries from 13 Brassica and related weed species grown in the field. Total plant GSL production on a ground area basis at mid-flowering ranged from 0.8 to 45.3 mmol m -2 . The variation derived equally from differences in biomass and GSL concentration, which were not correlated in either root or shoot tissues. Roots (0-0.15 m) contributed an average of 23.6% (range 2-81%) of the total plant GSLs, their contribution limited by low biomass rather than GSL concentration, which was usually similar or higher than that of shoots. The GSL concentrations in root and shoot tissues did not correlate significantly with seed levels in any of the species, so selection for higher plant GSL production to enhance biofumigation potential cannot be based on seed GSL levels. The types of GSLs present in the tissues varied considerably between species but were consistent within species. In contrast, the concentration of individual and total GSLs in both root and shoot tissues varied four to ten-fold both between and within all species. Shoots contained predominately aliphatic GSLs, while aromatic GSLs, particularly 2-phenylethyl GSL, were dominant in the roots of all entries. Indolyl GSLs were present in all tissues but at low concentrations (< 1 μmol g -1 ). The variation in the biomass, GSL profiles and concentrations in both roots and shoots provide significant scope to select or develop brassicas with enhanced biofumigation potential. Further studies on the efficacy of the various GSL hydrolysis products to suppress target organisms in soil are required to fully exploit biofumigation as a part of integrated pest management.

Mycorrhizal sink strength influences whole plant carbon balance of Trifolium repens L

Abstract: A comparative analysis of daily carbon (C) budgets and aspects of the C physiology of clover (Trifolium repens L.) colonized by vesicular-arbuscular (VA) mycorrhizal fungi was carried out over a 70 d growth period under conditions designed to ensure that shoots of mycorrhizal (M) and non-mycorrhizal (NM) plants were of similar nutrient status. C budgets did not differ on day 24 but by day 42 M plants had a significantly higher rate of photosynthesis than their NM counterparts when expressed on a whole shoot basis or unit dry weight basis. As both sets of plants were of the same size it was concluded that this greater C gain was the result of increased sink strength provided by the mycorrhizal fungus. By day 53 M plants had become larger than their uncolonized counterparts and a sink-induced stimulation in the rate of photosynthesis was no longer apparent. M plants had higher root sucrose, glucose and fructose pools from day 24. Analyses suggested that these sugars were utilized for trehalose and lipid synthesis, for the production of the large extramatrical mycelium and for the support of the respiratory demands of the M root system. Increased C allocation to roots of M plants was associated with a stimulation of the activities of cell wall and cytoplasmic invertases and of sucrose synthase in roots colonized by VA fungi. Such increases in enzyme activity may provide the mechanism enabling increased partitioning of carbohydrate both to the M root system and the fungal symbiont.

Cadmium toxicity effects on growth, mineral and chlorophyll contents, and activities of stress related enzymes in young maize plants (Zea mays L.)

Abstract: Plants were cultivated in a nutrient solution containing increasing cadmium concentrations (i.e. 0.001–25 µM), under strictly controlled growth conditions. Changes in both growth parameters and enzyme activities, directly or indirectly related to the cellular free radical scavenging systems, were studied in roots and leaves of 14-day-old maize plants (Zea mays L., cv. Volga) as a result of Cd uptake. A decrease in both shoot length and leaf dry biomass was found to be significant only when growing on 25 µM Cd, whereas concentrations of chlorophyll pigments in the 4th leaf decreased from 1.7 µM Cd on. Changes in enzyme activities occurred at lower Cd concentrations in solution leading to lower threshold values for Cd contents in plants than those observed for growth parameters. Peroxidase (POD; E.C. 1.11.1.7) activity increased in the 3rd and 4th leaf, but not in roots. In contrast, glucose-6-phosphate dehydrogenase (G6PDH; E.C. 1.1.1.49), isocitrate dehydrogenase (ICDH; E.C. 1.1.1.42) and malic enzyme (ME; E.C. 1.1.1.40) activities decreased in the 3rd leaf. According to the relationship between the POD activity and the Cd content, a toxic critical value was set at 3 mg Cd per kg dry matter in the 3rd leaf and 5 mg Cd per kg dry matter in the 4th. Anionic POD were determined both in root and leaf protein extracts; however, no changes in the isoperoxidase pattern were detected in case of Cd toxicity. Results show that in contrast with growth parameters, the measurement of enzyme activities may be included as early biomarkers in a plant bioassay to assess the phytotoxicity of Cd-contaminated soils on maize plants.

The effect of commercial humic acid on tomato plant growth and mineral nutrition

Abstract: The effects of humic acids extracted from two commercially‐available products (CP‐A prepared from peat and CP‐B prepared from leonardite) on the growth and mineral nutrition of tomato plants (Lycopersicon esculentum L.) in hydroponics culture were tested at concentrations of 20 and 50 mg L‐1. Both the humic acids tested stimulated plants growth. The CP‐A stimulated only root growth, especially at 20 mg L‐1 [23% and 22% increase over the control, on fresh weight basis (f.w.b.), and dry weight basis (d.w.b.), respectively]. In contrast, CP‐B showed a positive effect on both shoots and roots, especially at 50 mg L‐1 (shoots: 8% and 9% increase over the control; roots: 18% and 16% increase over the control, on f.w.b. and d.w.b., respectively). Total ion uptake by the plants was affected by the two products. In particular, CP‐A showed an increase in the uptake of nitrogen (N), phosphorus (P), iron (Fe), and copper (Cu), whereas, CP‐B showed positive effects for N, P, and Fe uptake. The change in the F...

Sources and consequences of seed mass variation in Banksia marginata (Proteaceae)

Abstract: 1 We examined the sources and consequences of seed mass variation in Banksia marginata occurring in fire-prone heath on nutrient-poor soils to determine factors influencing seed size and possible fitness benefits of large seeds. 2 Individual seed mass varied fivefold. Variation occurred among populations (29% of total), among years (10%) and among plants (plants, 6%; year × plants, 13%), but was most pronounced within plants (42%). Within plants, seed mass variation was greater within infructescences (35%) than among infructescences (7%). 3 Seed mass variation within infructescences was not related to whether follicles contained one or two seeds. Seed mass was also unaffected by ovule position within follicles and follicle position within infructescences. 4 Seed mass variation among infructescences and plants was related to the limited availability of nutrient resources during seed provisioning. Mean seed mass was negatively related to seed number per infructescence and per plant. When resources decreased late in the flowering season and after defoliation, seed mass declined by 7–10% and seed number by 31–45%. When resources increased after inflorescence removal, seed mass increased by 8% but seed number was unaffected. Plants thus had only a limited capacity to maintain seed mass by adjusting seed number when resources varied. 5 The N and P contents of seeds (mg seed−1) increased linearly with seed mass, indicating costs of producing larger seeds in terms of limited environmental nutrients. 6 Seedling size increased with seed mass, implying fitness benefits of larger seeds in terms of increased seedling establishment on nutrient-poor soils. Seed mass had little or no effect on seed germination, relative growth rates and root:shoot ratios. 7 Although stabilizing selection should eliminate seed mass variation occurring within plants, such variation persists because resource constraints limit the ability of plants to control individual seed size.

Assessment of salt tolerance in rice cultivars in response to salinity problems in California

Abstract: Stringent requirements for water holding for California rice producers who use pesticides have resulted in the loss of stand and visible symptoms of leaf damage for some growers A field survey and subsequent series of experiments were conducted to determine the range of salt tolerance among 11 cultivars of rice (Oryza saliva L) that are common to northern California rice-growing areas A field assessment made on several farms led to the conclusion that growth reduction and stand loss were correlated with high salinity in soil mud and water Plants from saline basins had significantly higher concentrations of leaf Na + and Cl - than those from less saline basins Greenhouse studies were conducted in sand cultures and flooded with saline waters having average electrical conductivities of approximately 1 (control), 3, 7, 11, 13, and 16 dS m -1 Salinity decreased emergence rates and final stand and led to reductions in shoot and root fresh and dry weights At the highest salinity, shoot weights were 20% of the control after 17 d Leaf tissues of plants grown at 16 dS m -1 had five times as much Na + and three times as much Cl - as controls Leaf concentration of K + was decreased by about 40% by salinity, but tissue levels of Ca 2+ and Mg 2+ were unaffected In a second experiment, salinity treatments were lowered to 08, 16, 32, 6, 8, and 10 dS m -1 There were significant differences in growth rates related to cultivar, but relative salt tolerance differences were negligible, leading to the conclusion that genetic differences among the rice cultivars are limited

The influence of arsenic chemical form and concentration on Spartina patens and Spartina alterniflora growth and tissue arsenic concentration

Abstract: Arsenic (As) uptake by two perennial coastal marsh grasses growing in hydroponic conditions was studied in relation to the chemical form and concentration of As added to nutrient solution A 4×3×2 factorial experiment was conducted with treatments consisting of four As chemical forms [arsenite, As(III); arsenate, As(V); monomethyl arsonic acid, MMAA; and dimethyl arsinic acid, DMAA], three As concentrations (02, 08, and 20 mg As L-1) and two plant species (Spartina patens and Spartina alterniflora) Arsenic phytoavailability and phytotoxicity were primarily determined by the As chemical form present in the nutrient solution, though As concentration also influenced both As availability and toxicity Application of As(V) increased root, shoot and total dry matter production; this positive plant growth response may be linked with P nutrition Organic arsenicals and As(III) were the most phytotoxic species to both marsh grasses when plant growth was considered Arsenic uptake and transport in plant were species-specific Phytoavailability of As followed the trend DMAA ≪MMAA ≅ As(V) < As(III) Root and shoot As concentrations significantly increased with increasing As application rates to the rooting medium, regardless of the As chemical form Upon absorption, inorganic arsenicals and MMAA were mainly accumulated in the root system, while DMAA was readily translocated to the shoot

Sugarcane shoot formation in an improved temporary immersion system

Abstract: A new protocol was established for sugarcane cv C-1051-73 shoot formation in a temporary immersion system The two-step protocol involves shoot formation in 50 ml of culture medium per explant and 10 mg l-1 paclobutrazol for 30 days followed by shoot elongation by exposure to 10 mg l-1 gibberellic acid for 15 days The multiplication rate was doubled in comparison with the conventional micropropagation protocol (Jimenez et al, 1995) and the cost has been reduced by 46% Three additional sugarcane varieties have been micropropagated according to this new protocol and results are comparable Temporary immersion-derived plants have also been compared with conventionally propagated plants in sugarcane fields for more than 9 months and their agricultural indicators of performance are similar

A plant growth promoting rhizobacterium and temperature effects on performance of 18 clones of potato

Abstract: A survey of genotypic responses to beneficial bacterium (Pseudomonas sp strain PsJN) was conductedin vitro andex vitro, under two temperature conditions, using eighteen clones of potato of different heat stress tolerance: temperate adapted cultivars Kennebec and Russet Burbank; heat tolerant DTO-2, DTO-28, DTO-33, LT-1, LT-2, LT-5, LT-6, LT-7, LT-8, LT-9, Y84-02, NDD277-2, Desiree, and Maine-47; and heat sensitive abscissic acid (ABA)-deficient mutants 11401-01 and 9120-05 Nodal explants taken from 6-week-old bacterized and non-bacterized control plantlets were culturedin vitro on a hormone-free potato nodal cutting medium, and placed at either 20/15 C or 33/25 C day/night temperature, 12h photoperiod and 250 µE m−2 s−1 mixture of fluorescent and incandescent light, for six weeks The tuberization response was studiedex vitro after two weeks acclimation of 2-week old plantlets at 33/25C The acclimated plantlets were transplanted to 3L plastic nursery pots containing peat-based Pro-Mix growing medium and placed in growth chambers at either 20/15 or 33/25 C day/night temperature, 12 h photoperiod, 475 μE m−2 s−1 light and ≈80% RH, for 12 weeks Compared to the non-bacterized controls, bacterization significantly increased stem length of 12, shoot biomass of 9, and root biomass of 2 clones at 20/15C; and stem length of 14, shoot biomass of 15, and root biomass of 13 clones at 33/25C High temperature increased length of internodes and had either no effect or slightly decreased node number Temperature increase had the most dramatic effect on root development An average shoot to root ratio decreased from 37 at 20/15 C to 17 at 33/25 C for non-bacterized plantlets and, respectively, from 43 to 15 for bacterized The beneficial effect of bacterization on root biomass was the most pronounced in LT-1 and Maine-47 at 20/15 C and LT-8, Maine 47, DTO-2, Kennebec, NDD277-2 and 11401-01 at 33/25C The temperature elevation did not significantly affect root biomass of LT-6, DTO-28 and Desiree Temperature stress caused severe reduction in tuber number and tuber fresh weight ABA-deficient mutants did not produce any tubers and LT-8, LT-9, Y84-027 and DTO-28 tuberized very poorly at 33/25C DTO-33, Desiree, LT-1 and Kennebec gave the highest number of tubers per pot and Kennebec, LT-1, Desiree and LT-7 the highest yields at this temperature There was no significant effect of bacterization on tuberization at 20/15 C but at 33/25 C bacterization significantly enhanced tuber number and weight in LT-7 and reduced tuber weight in DTO-2 Although there was no clear link between thein vitro response of particular clones to bacterization and their heat stress tolerance, improvement ofex vitro performance of heat tolerant LT-7 indicates that rhizosphere bacteria may play a role in clonal adaptation of potato to heat stress

Phytoremediation of a Radiocesium-Contaminated Soil: Evaluation of Cesium-137 Bioaccumulation in the Shoots of Three Plant Species

Abstract: A field study was conducted to investigate the potential of three plant species for phytoremediation of a 137 Cs-contaminated site. Approximately 40-fold more 137 Cs was removed from the contaminated soil in shoots of red root pigweed (Amaranthus retroflexus L.) than in those of Indian mustard [Brassica juncea (L.) Czern] and tepary bean (Phaseolus acutifolius A. Gray). The greater potential for 137 Cs removal from the soil by A. retroflexus was associated with both high concentration of 137 Cs in shoots and high shoot biomass production. Approximately 3% of the total 137 Cs was removed from the top 15 cm of the soil (which contained most of the soil radiocesium) in shoots of 3-mo-old A. retroflexus plants. Soil leaching tests conducted with 0.1 and 0.5 M NH 4 NO 3 solutions eluted as much as 15 and 19%, respectively, of the soil 137 Cs. Addition of NH 4 NO 3 to the soil, however, had no positive effect on 137 Cs accumulation in shoots in any of the species investigated. It is proposed that either NH 4 NO 3 solution quickly percolated through the soil before interacting at specific 137 Cs binding sites or radiocesium mobilized by NH 4 NO 3 application moved below the rhizosphere, becoming unavailable for root uptake. Further research is required to optimize the phytotransfer of the NH 4 NO 3 -mobilized 137 Cs. With two croppings of A. retroflexus per year and a sustained rate of extraction, phytoremediation of this 137 Cs-contaminated soil appears feasible in <15 yr.

The functional ecology of shoot architecture in sun and shade plants of Heteromeles arbutifolia M. Roem., a Californian chaparral shrub.

Abstract: The functional roles of the contrasting morphologies of sun and shade shoots of the evergreen shrub Heteromeles arbutifolia were investigated in chaparral and understory habitats by applying a three-dimensional plant architecture simulation model, YPLANT. The simulations were shown to accurately predict the measured frequency distribution of photosynthetic photon flux density (PFD) on both the leaves and a horizontal surface in the open, and gave reasonably good agreement for the more complex light environment in the shade. The sun shoot architecture was orthotropic and characterized by steeply inclined (mean = 71o) leaves in a spiral phyllotaxy with short internodes. This architecture resulted in relatively low light absorption efficiencies (EA) for both diffuse and direct PFD, especially during the summer when solar elevation angles were high. Shade shoots were more plagiotropic with longer internodes and a pseudo-distichous phyllotaxis caused by bending of the petioles that positioned the leaves in a nearly horizontal plane (mean = 5o). This shade-shoot architecture resulted in higher EA values for both direct and diffuse PFD as compared to those of the sun shoots. Differences in EA between sun and shade shoots and between summer and winter were related to differences in projection efficiencies as determined by leaf and solar angles, and by differences in self shading resulting from leaf overlap. The leaves exhibited photosynthetic acclimation to the sun and the shade, with the sun leaves having higher photosynthetic capacities per unit area, higher leaf mass per unit area and lower respiration rates per unit area than shade leaves. Despite having 7 times greater available PFD, sun shoots absorbed only 3 times more and had daily carbon gains only double of those of shade shoots. Simulations showed that sun and shade plants performed similarly in the open light environment, but that shade shoots substantially outperformed sun shoots in the shade light environment. The shoot architecture observed in sun plants appears to achieve an efficient compromise between maximizing carbon gain while minimizing the time that the leaf surfaces are exposed to PFDs in excess of those required for light saturation of photosynthesis and therefore potentially photoinhibitory.

HASTY: a gene that regulates the timing of shoot maturation in Arabidopsis thaliana

Abstract: In Arabidopsis thaliana, leaves produced at different stages of shoot development can be distinguished by the distribution of trichomes on the abaxial and adaxial surfaces. Leaves produced early in the development of the rosette (juvenile leaves) have trichomes on their adaxial, but not their abaxial surface, whereas leaves produced later in rosette development (adult leaves) have trichomes on both surfaces. In order to identify genes that regulate the transition between these developmental phases we screened for mutations that accelerate the production of leaves with abaxial trichomes. 9 alleles of the HASTY gene were recovered in this screen. In addition to accelerating the appearance of adult leaves these mutations also accelerate the loss of adaxial trichomes (a trait typical of bracts), reduce the total number of leaves produced by the shoot, and have a number of other effects on shoot morphology. The basis for this phenotype was examined by testing the interaction between hasty and genes that affect flowering time (35S::LEAFY, 35S::APETALA1, terminal flower1), gibberellin production (ga1-3) or perception (gai), and floral morphogenesis (leafy, apetala1, agamous). We found that hasty increased the reproductive competence of the shoot, and that its does not require gibberellin or a gibberellin response for its effect on vegetative or reproductive development. The phenotype of hasty is not suppressed by leafy, apetala1 and agamous, demonstrating that this phenotype does not result from the inappropriate expression of these genes. We suggest that HASTY promotes a juvenile pattern of vegetative development and inhibits flowering by reducing the competence of the shoot to respond to LEAFY and APETALA1.

Tomato Root and Shoot Responses to Salt Stress Under Different levels of Phosphorus Nutrition

Abstract: Crops differ in their ability to grow under saline conditions and their responses are quite variable and not fully understood. This study was conducted to evaluate the root and shoot responses of tomato to salt stress conditions under different levels of phosphorus (P) nutrition. Tomato seedlings (cv Riogrande) were grown in 500 mL glass jars containing Hoagland's solutions which were salinized by four levels of NaCl salt (0,50,100, and 150 mM NaCl) and/or enriched with three P levels (0.5,1, and 2 mM P) making nine combination treatments. Plants were harvested at the vegetative growth stage and data were collected for root and shoot characteristics. The results indicate that increasing salinity stress was accompanied by significant reductions in shoot weight, plant height, number of leaves per plant, and a significant increase in leaf osmotic potential and peroxidase activity regardless of the level of P supplied. Both root length and root surface area per plant were decreased significantly unde...

Micropropagation of Vitex negundo L., a woody aromatic medicinal shrub, through high-frequency axillary shoot proliferation.

Abstract: A protocol is described for rapid and large-scale propagation of the woody aromatic and medicinal shrub Vitex negundo by in vitro culture of nodal segments from mature plants. Of the three different cytokinins – N6-benzyladenine (BA), kinetin, and thidiazuron – evaluated as supplements to Murashige and Skoog (MS) medium, BA at an optimal concentration of 2.0 mg/l was most effective in inducing bud break. Although callus-free multiple-shoot formation was a function of cytokinin activity alone, faster bud break coupled with an enhanced frequency of shoot development (92%) and internode elongation were dependent on the synergistic influence of gibberellic acid (GA3) when used at an optimal concentration (0.4 mg/l) along with BA (2.0 mg/l). The frequency of shoot proliferation was markedly influenced by the explanting season. By repeated subculturing of nodal segments harvested from the in vitro-formed axenic shoots on MS containing 1.0 mg/l BA and 0.4 mg/l GA3, prolific shoot cultures free from proximal callusing and showing a high-frequency multiplication rate were established. The percentage shoot multiplication (98–100%) as well as the number of shoots per node (six to eight) were highest during the first three culture passages, after which there was a gradual decline in shoot development. Rooting was best induced (94%) in shoots excised from proliferated shoot cultures on half-strength MS medium augmented with an optimal combination of indole-3-acetic acid and indole-3-butyric acid each at 1.0 mg/l. Vermi-compost was the most suitable planting substrate for hardening inside a plant growth chamber and its use ensured high-frequency survival (93%) of regenerated plants prior to outdoor transfer. Micropropagated plants established in garden soil were uniform and identical to the donor plant with respect to growth characteristics as well as vegetative and floral morphology.

Accumulation of flavonoids and related compounds in birch induced by UV-B irradiance

Abstract: A growth chamber experiment was conducted to examine the effects of UV-B exposure (4.9 kJ m(-2) day(-1) of biologically effective UV-B, 280-320 nm) on shoot growth and secondary metabolite production in Betula pendula (Roth) and B. resinifera (Britt.) seedlings originating from environments in Finland, Germany and Alaska differing in solar UV-B radiation and climate. Neither shoot growth nor the composition of secondary metabolites was affected by UV-B irradiance, but the treatment induced significant changes in the amounts of individual secondary metabolites in leaves. Leaves of seedlings exposed to UV-B radiation contained higher concentrations of several flavonoids, condensed tannins and some hydroxycinnamic acids than leaves of control seedlings that received no UV-B radiation. At the population level, there was considerable variation in secondary metabolite responses to UV-B radiation: among populations, the induced response was most prominent in Alaskan populations, which were adapted to the lowest ambient UV-B radiation environment. I conclude that solar UV-B radiation plays an important role in the formation of secondary chemical characteristics in birch trees.

Rapid clonal multiplication through in vitro axillary shoot proliferation of Aegle marmelos (L.) Corr., a medicinal tree.

Abstract: Rapid clonal multiplication of Aegle marmelos (L.) Corr. (Rutaceae), a medicinal tree, was achieved by enhanced axillary bud proliferation in young single-node segments of a 25-year-old tree cultured in Murashige and Skoog (MS) nutrient medium. Bud break was dependent on cytokinin supply, but the synergistic combination of 2.5 mg l–1 6-benzylaminopurine (BAP) and 1.0 mg l–1 indole-3-acetic acid (IAA) induced the formation of 12.1 shoots of up to 5.2 cm length in 48% of the explants after 7 weeks of culture. Explants of in-vitro-grown shoots – node, whole leaf, shoot tip and internode – were subcultured in the presence of 0.05–2.5 mg l–1 BAP to produce 11.3, 18.4, 5.3 and 3.2 shoots and shoot buds at a 100%, 70%, 95% and 40% rate respectively, in 7 weeks. Different shoot nodes and leaves were equally regenerative and adventitious organogenesis in the latter was confined to cut petiolar ends. Nodal explants responded most favourably at low BAP (0.05–0.1 mg l–1) and produced uniform (3.8–5.3 cm) shoots facilitating their simultaneous harvest for rooting. Repeated subculturing through five cycles of nodes and leaves of shoot cultures enabled continuous production of healthy callus-free shoots without any sign of decline. Shoot cuttings (3.0–5.2 cm) were best rooted in half-strength MS medium with 0.5 mg l–1 IAA (70%) or 10.0 mg l–1 indole-3-butyric acid (90%). Eighty-eight percent of the rooted plants were established in polybags after hardening.

Growth, mineral acquisition, and water use by mycorrhizal wheat grown under water stress

Abstract: Plants colonized with arbuscular mycorrhizal (AM) fungi generally have greater growth and acquisition of mineral nutrients, and often have greater ability to withstand drought compared to nonmycorrhizal (nonAM) plants. This study determined effects of water stress (WS) versus no WS (nonWS) and the AM fungus Glomus monosporum (AM vs nonAM) on growth, acquisition of phosphorus (P), zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe), and water use in two durum wheat (Triticum durum Desf.) cultivars exhibiting differences in resistance to WS. Plants were grown on soil [low P silty clay (Typic Xerochrept, pH=8.1)] and sand mixtures in a greenhouse. Shoot and root dry matter (DM), total root length (RL), and root colonization with AM for plants grown under non WS were higher than for plants grown under WS. Much of the reduction in DM was overcome by AM plants grown under WS. The ‘drought‐resistant’ wheat cultivar CR057 had higher AM root colonization than the ‘drought‐sensitive’ cultivar CR006 when ...

Studies of iron transport by arbuscular mycorrhizal hyphae from soil to peanut and sorghum plants

Abstract: The influence of an arbuscular mycorrhizal (AM) fungus on phosphorus (P) and iron (Fe) uptake of peanut (Arachis hypogea L.) and sorghum (Sorghum bicolor L.) plants was studied in a pot experiment under controlled environmental conditions. The plants were grown for 10 weeks in pots containing sterilised calcareous soil with two levels of Fe supply. The soil was inoculated with rhizosphere microorganisms only or with rhizosphere microorganisms together with an AM fungus (Glomus mosseae [Nicol. & Gerd.] Gerdemann & Trappe). An additional small soil compartment accessible to hyphae but not roots was added to each pot after 6 weeks of plant growth. Radiolabelled P and Fe were supplied to the hyphae compartment 2 weeks after addition of this compartment. After a further 2 weeks, plants were harvested and shoots were analysed for radiolabelled elements. In both plant species, P uptake from the labelled soil increased significantly more in shoots of mycorrhizal plants than non-mycorrhizal plants, thus confirming the well-known activity of the fungus in P uptake. Mycorrhizal inoculation had no significant influence on the concentration of labelled Fe in shoots of peanut plants. In contrast, 59Fe increased in shoots of mycorrhizal sorghum plants. The uptake of Fe from labelled soil by sorghum was particularly high under conditions producing a low Fe nutritional status of the plants. These results are preliminary evidence that hyphae of an arbuscular mycorrhizal fungus can mobilise and/or take up Fe from soil and translocate it to the plant.

Uptake and translocation of phosphate by pho2 mutant and wild-type seedlings of Arabidopsis thaliana

Abstract: The pho2 mutant of Arabidopsis thaliana (L.) Heynh. accumulates excessive Pi (inorganic phosphate) concentrations in shoots compared to wild-type plants (E. Delhaize and P. Randall, 1995, Plant Physiol. 107: 207–213). In this study, a series of experiments was conducted to compare the uptake and translocation of Pi by pho2 with that of wild-type plants. The pho2 mutants had about a twofold greater Pi uptake rate than wild-type plants under P-sufficient conditions and a greater proportion of the Pi taken up accumulated in shoots of pho2. When shoots were removed, the uptake rate by roots was found to be similar for both genotypes, suggesting that the greater Pi uptake by the intact pho2 mutant is due to a greater shoot sink for Pi. Although pho2 mutants could recycle 32Pi from shoots to roots through phloem the proportion of 32Pi translocated to roots was less than half of that found in wild-type plants. When transferred from P-sufficient to P-deficient solutions, Pi concentrations in pho2 roots had a similar depletion rate to wild-type roots despite pho2 shoots having a fourfold greater Pi concentration than wild-type shoots throughout the experiment. We suggest that the pho2 phenotype could result from a partial defect in Pi transport in the phloem between shoots and roots or from an inability of shoot cells to regulate internal Pi concentrations.