Showing papers on "Shoot published in 2004"

Arbuscular mycorrhizal influence on leaf water potential, solute accumulation, and oxidative stress in soybean plants subjected to drought stress

Abstract: This study investigated several aspects related to drought tolerance in arbuscular mycorrhizal (AM) soybean plants. The investigation included both shoot and root tissues in order to reveal the preferred target tissue for AM effects against drought stress. Non-AM and AM soybean plants were grown under well-watered or drought-stressed conditions, and leaf water status, solute accumulation, oxidative damage to lipids, and other parameters were determined. Results showed that AM plants were protected against drought, as shown by their significantly higher shoot-biomass production. The leaf water potential was also higher in stressed AM plants (-1.9 MPa) than in non-AM plants (-2.5 MPa). The AM roots had accumulated more proline than non-AM roots, while the opposite was observed in shoots. Lipid peroxides were 55% lower in shoots of droughted AM plants than in droughted non-AM plants. Since there was no correlation between the lower oxidative damage to lipids in AM plants and the activity of antioxidant enzymes, it seems that first the AM symbiosis enhanced osmotic adjustment in roots, which could contribute to maintaining a water potential gradient favourable to the water entrance from soil into the roots. This enabled higher leaf water potential in AM plants during drought and kept the plants protected against oxidative stress, and these cumulative effects increased the plant tolerance to drought.

QTLs for Na + and K + uptake of the shoots and roots controlling rice salt tolerance

Abstract: An F2 and an equivalent F3 population derived from a cross between a high salt-tolerance indica variety, Nona Bokra, and a susceptible elite japonica variety, Koshihikari, were produced. We performed QTL mapping for physiological traits related to rice salt-tolerance. Three QTLs for survival days of seedlings (SDSs) under salt stress were detected on chromosomes 1, 6 and 7, respectively, and explained 13.9% to 18.0% of the total phenotypic variance. Based on the correlations between SDSs and other physiological traits, it was considered that damage of leaves was attributed to accumulation of Na+ in the shoot by transport of Na+ from the root to the shoot in external high concentration. We found eight QTLs including three for three traits of the shoots, and five for four traits of the roots at five chromosomal regions, controlled complex physiological traits related to rice salt-tolerance under salt stress. Of these QTLs, the two major QTLs with the very large effect, qSNC-7 for shoot Na+ concentration and qSKC-1 for shoot K+ concentration, explained 48.5% and 40.1% of the total phenotypic variance, respectively. The QTLs detected between the shoots and the roots almost did not share the same map locations, suggesting that the genes controlling the transport of Na+ and K+ between the shoots and the roots may be different.

Indices of drought tolerance in wheat genotypes at early stages of plant growth

Abstract: Thirty diverse genotypes of bread wheat were evaluated for seed vigour index, germination percentage, root length, shoot length, root-to-shoot length ratio, coleoptile length and osmotic membrane stability under laboratory conditions. Considerable variation was observed for all the characters. Discrimination among the genotypes on the basis of mean values was better under normal than under moisture stress conditions, indicating suppression of variability under moisture stress conditions. Comparison of mean performance under normal and osmotic stress conditions indicated that the seed vigour index was the most sensitive trait, followed by shoot length, germination percentage and root length. The root-to-shoot length ratio, however, increased under osmotic stress. The magnitude of genetic components of variance and heritability were, in general, lower under osmotic stress than under normal conditions. All the characters except germination percentage, shoot length and coleoptile length showed considerable genetic variability. Heritability in the broad sense was also moderate to high for all the characters under both environments. Due to high heritability and genetic advance great benefit from selection can be expected for the osmotic membrane stability of leaf segments and root-to-shoot length ratio. Moderate progress can be expected from root length and seed vigour index. Correlation studies indicated that the osmotic membrane stability of the leaf segment was the most important trait, followed by root-to-shoot ratio and root length on the basis of their relationships with other traits.

Interactions between selenium and sulphur nutrition in Arabidopsis thaliana

Abstract: Selenium (Se) is an essential plant micronutrient, but is toxic at high tissue concentrations. It is chemically similar to sulphur (S), an essential plant macronutrient. The interactions between Se and S nutrition were investigated in the model plant Arabidopsis thaliana (L.) Heynh. Arabidopsis plants were grown on agar containing a complete mineral complement and various concentrations of selenate and sulphate. The Se/S concentration ratio in the shoot ([Se](shoot)/[S](shoot)) showed a complex dependence on the ratio of selenate to sulphate concentration in the agar ([Se](agar)/[S](agar)). Increasing [S](agar) increased shoot fresh weight (FW) and [S](shoot), but decreased [Se](shoot). Increasing [Se](agar) increased both [Se](shoot) and [S](shoot), but reduced shoot FW. The reduction in shoot FW in the presence of Se was linearly related to the shoot Se/S concentration ratio. These data suggest (i) that Se and S enter Arabidopsis through multiple transport pathways with contrasting sulphate/selenate selectivities, whose activities vary between plants of contrasting nutritional status, (ii) that rhizosphere sulphate inhibits selenate uptake, (iii) that rhizosphere selenate promotes sulphate uptake, possibly by preventing the reduction in the abundance and/or activity of sulphate transporters by sulphate and/or its metabolites, and (iv) that Se toxicity occurs because Se and S compete for a biochemical process, such as assimilation into amino acids of essential proteins.

Field response of wheat to arbuscular mycorrhizal fungi and drought stress.

Abstract: Mycorrhizal plants often have greater tolerance to drought than nonmycorrhizal plants. This study was conducted to determine the effects of arbuscular mycorrhizal (AM) fungi inoculation on growth, grain yield and mineral acquisition of two winter wheat (Triticum aestivum L.) cultivars grown in the field under well-watered and water-stressed conditions. Wheat seeds were planted in furrows after treatment with or without the AM fungi Glomus mosseae or G. etunicatum. Roots were sampled at four growth stages (leaf, tillering, heading and grain-filling) to quantify AM fungi. There was negligible AM fungi colonization during winter months following seeding (leaf sampling in February), when soil temperature was low. During the spring, AM fungi colonization increased gradually. Mycorrhizal colonization was higher in well-watered plants colonized with AM fungi isolates than water-stressed plants. Plants inoculated with G. etunicatum generally had higher colonization than plants colonized with G. mosseae under both soil moisture conditions. Biomass and grain yields were higher in mycorrhizal than nonmycorrhizal plots irrespective of soil moisture, and G. etunicatum inoculated plants generally had higher biomass and grain yields than those colonized by G. mosseae under either soil moisture condition. The mycorrhizal plants had higher shoot P and Fe concentrations than nonmycorrhizal plants at all samplings regardless of soil moisture conditions. The improved growth, yield and nutrient uptake in wheat plants reported here demonstrate the potential of mycorrhizal inoculation to reduce the effects of drought stress on wheat grown under field conditions in semiarid areas of the world.

Mycorrhizal inoculant alleviates salt stress in Sesbania aegyptiaca and Sesbania grandiflora under field conditions: evidence for reduced sodium and improved magnesium uptake

Abstract: A field experiment was conducted to examine the effect of the arbuscular mycorrhizal fungus Glomus macrocarpum and salinity on growth of Sesbania aegyptiaca and S. grandiflora. In the salt-stressed soil, mycorrhizal root colonisation and sporulation was significantly higher in AM-inoculated than in uninoculated plants. Mycorrhizal seedlings had significantly higher root and shoot dry biomass production than non-mycorrhizal seedlings grown in saline soil. The content of chlorophyll was greater in the leaves of mycorrhiza-inoculated as compared to uninoculated seedlings. The number of nodules was significantly higher in mycorrhizal than non-mycorrhizal plants. Mycorrhizal seedling tissue had significantly increased concentrations of P, N and Mg but lower Na concentration than non-mycorrhizal seedlings. Under salinity stress conditions both Sesbania sp. showed a high degree of dependence on mycorrhizae, increasing with the age of the plants. The reduction in Na uptake together with a concomitant increase in P, N and Mg absorption and high chlorophyll content in mycorrhizal plants may be important salt-alleviating mechanisms for plants growing in saline soil.

Interactions Between Trichoderma harzianum Strain T22 and Maize Inbred Line Mo17 and Effects of These Interactions on Diseases Caused by Pythium ultimum and Colletotrichum graminicola

Abstract: Seed treatment with Trichoderma harzianum strain T22, which results in colonization of plant roots but little or no colonization of shoots or leaves, had substantial effects on growth of and disease expression in maize inbred line Mo17. Shoots and roots of 10-day-old seedlings grown in a sandy loam field soil were larger (roots were nearly twice as long) in the presence of T22 than in its absence. Both main and secondary roots were increased in size and area and the root hair area was greater with T22. However, root hair area per unit of root length was greater in control plants. Increased growth probably was due to direct stimulation of plant growth in addition to effects from biological control of deleterious microflora. Seedlings of Mo17 grown in autoclaved or mefenoxamtreated sandy loam field soil were larger than those produced in untreated soil. However, seedlings grown in the presence of T22, either in treated or untreated soil, were larger than those produced in its absence. Infestation o...

Do phosphorus nutrition and iron plaque alter arsenate (As) uptake by rice seedlings in hydroponic culture

Abstract: Summary • A hydroponic experiment was conducted to investigate the effect of phosphorus (P) nutrition and iron plaque on root surfaces on arsenate uptake by, and translocation within, the seedlings of three cultivars of rice (Oryza sativa). • Supply of 0.5 mg As l−1 had no significant effects on dry weights of shoots or roots, but resulted in elevated concentrations of As in tissues, particularly in roots. Rice roots appeared reddish after 24 h in –P solution (without P), indicating the formation of iron plaque. • Arsenic concentrations in iron plaque (determined in dithionite–citrate–bicarbonate (DCB)-extracts) were significantly higher in –P plants (up to 1180 mg kg−1 in cultivar CDR22) than in +P plants. Concentrations of arsenic in shoots were significantly lower in –P plants than in +P plants. This indicates that iron plaque might sequestrate As, and consequently reduce the translocation of arsenic from roots to shoots. • Values for the total uptake of As show that As in –P rice plants was mainly concentrated in the DCB-extracts or on the surface of rice roots, whereas most arsenic in +P plants was accumulated in the roots. Arsenic significantly decreased the concentrations of iron (Fe) in roots and shoots (P < 0.001) and slightly reduced P concentrations in shoots, except for the –P cultivar CDR22.

Sorghum and salinity: I. Response of growth, water relations, and ion accumulation to NaCl salinity

Abstract: Crops grown in salt affected soils may suffer from drought stress, ion toxicity, and mineral deficiency leading to reduced growth and productivity. The present study was conducted to determine how salinity affects growth, water relations, and accumulation of cations of nutritional importance in various organs of grain sorghum [Sorghum bicolor (L.) Moench]. Two Kenyan sorghum varieties, Serena and Seredo, were grown in a greenhouse in quartz sand supplied with a complete nutrient solution to which 0 (control), 50, 100, 150, 200, and 250 mM NaCl was added. The 250 mM NaCl treatment significantly reduced the relative shoot growth rates, measured 25 d after the start of salt application, by 75 and 73%, respectively, for Serena and Seredo, and stem dry weight by 75 and 53%. In a similar way, young leaves were affected, with leaf blades of both varieties being reduced by 67% while sheaths were reduced by 83 and 87% for Serena and Seredo, respectively. Leaf water potential, osmotic potential, leaf pressure potential, and relative water content significantly declined with increasing salt stress. Roots and stems accumulated substantial amounts of sodium, saturating at 150 mM external NaCl. Accumulation of K+ and Ca2+ in the roots, stems, and leaves was strongly inhibited by salinity. Magnesium concentration of the roots was minimally impaired but that of the stems and leaves was strongly affected. Leaves continuously accumulated sodium, which was preferentially deposited in the sheaths. Mature leaves contained more Ca2+ and Mg2+ than young ones. The two sorghum varieties appear to sequester Na+ predominantly in roots, stems, leaf sheaths, and older leaf blades sparing the growing tissues as a salt tolerance mechanism. Nevertheless, greatly reduced concentrations of Ca2+, K+, and Mg2+ in leaves under salinity could cause cation deficiency which reduces plant growth.

Assessment of conditions affecting Agrobacterium -mediated soybean transformation using the cotyledonary node explant

Abstract: Conditions affecting Agrobacterium-mediated transformation of soybean [Glycine max (L.) Merr.], including seed vigor of explant source, selection system, and cocultivation conditions, were investigated. A negative correlation between seed sterilization duration and seed vigor, and a positive correlation between seed vigor and regenerability of explants were observed in the study, suggesting that use of high vigor seed and minimum seed sterilization duration can further improve transformation efficiency. Selection schemes using glufosinate or bialaphos as selective agents in vitro were assessed. Glufosinate selection enhanced soybean transformation as compared to bialaphos. The use of 6 mg L-1 glufosinate during shoot induction and shoot elongation stages yielded higher final transformation efficiency ranging from 2.0% to 6.3% while bialaphos at 4 to 6 mg L-1 gave 0% to 2.1% efficiency. Including cysteine and DTT during cocultivation increased the transformation efficiency from 0.2–0.9% to 0.6–2.9%. This treatment also improved T-DNA transfer as indicated by enhanced transient GUS expression. Shoot regeneration and Agrobacterium infection were attained in twelve soybean cultivars belonging to maturity groups I-VI. These cultivars maybe amenable to genetic transformation and may provide a valuable tool in soybean improvement programs.

The effects of salt stress on growth, nitrate reduction and proline and glycinebetaine accumulation in Prosopis alba

Abstract: Prosopis alba (algarrobo) is one of the most important salt-tolerant legumes used in the food and furniture industries. The effects of salinity on some growth and physiological parameters in algarrrobo seedlings were investigated. 17-Day-old seedlings were subjected to three salt treatments by adding NaCl to the growth medium in 50 mmol.L-1 increments every 24 h until the final concentrations of 0, 300 and 600 mmol.L-1 were reached. Only the highest NaCl concentration affected all of the considered parameters. Thus, 600 mmol.L-1 NaCl caused a significant reduction in root and shoot growth, but an increase in the root/shoot ratio. Leaf relative water content, nitrate content and nitrate reductase activity in leaves and roots were also decreased. At 300 and 600 mmol.L-1, the glycinebetaine content was significantly increased in both leaves and roots but this was not found for proline content. Total soluble carbohydrates increased only in roots. The results suggest that glycinebetaine enhancement may be important for osmotic adjustment in Prosopis alba under salinity stress.

The homeobox genes ATHB12 and ATHB7 encode potential regulators of growth in response to water deficit in Arabidopsis

Abstract: The Arabidopsisthaliana homeodomain leucine-zipper gene ATHB7, which is active specifically under water deficit conditions, is proposed to act as a negative regulator of growth (Soderman et al., 1996, Plant J. 10: 375 381; Hjellstrom et al., 2003, Plant Cell Environ 26: 1127 1136). In this report we demonstrate that the paralogous gene, ATHB12, has a similar expression pattern and function. ATHB12,like ATHB7,was up-regulated during water deficit conditions, the up-regulation being dependent on abscisic acid (ABA) and on the activity of the Ser/Thr phosphatases ABI1 and ABI2. Plants that are mutant for ATHB12, as a result of T-DNA insertions in the ATHB12 gene, showed a reduced sensitivity to ABA in root elongation assays, whereas transgenic Arabidopsis plants expressing ATHB12 and/orATHB7 as driven by the CaMV 35S promoter were hypersensitive in this response compared to wild-type. High-level expression of either gene also resulted in a delay in inflorescence stem elongation growth and caused plants to develop rosette leaves with a more rounded shape, shorter petioles, and increased branching of the inflorescence stem. Transgenic Arabidopsisplants expressing the reporter geneuidA under the control of the ATHB12promoter showed marker gene activity in axillary shoot primordia, lateral root primordia, inflorescence stems and in flower organs. Treatment of plants with ABA or water deficit conditions caused the activity of ATHB12to increase in the inflorescence stem, the flower organs and the leaves, and to expand into the vasculature of roots and the differentiation/elongation zone of root tips. Taken together, these results indicate that ATHB12 and ATHB7 act to mediate a growth response to water deficit by similar mechanisms.

Phylogenetic variation in the shoot mineral concentration of angiosperms

Abstract: The calcium (Ca) concentration of plant shoot tissues varies systematically between angiosperm orders. The phylogenetic variation in the shoot concentration of other mineral nutrients has not yet been described at an ordinal level. The aims of this study were (1) to quantify the shoot mineral concentration of different angiosperm orders, (2) to partition the phylogenetic variation in shoot mineral concentration between and within orders, (3) to determine if the shoot concentration of different minerals are correlated across angiosperm species, and (4) to compare experimental data with published ecological survey data on 81 species sampled from their natural habitats. Species, selected pro rata from different angiosperm orders, were grown in a hydroponic system under a constant external nutrient regime. Shoots of 117 species were sampled during vegetative growth. Significant variation in shoot carbon (C), calcium (Ca), potassium (K), and magnesium (Mg) concentration occurred between angiosperm orders. There was no evidence for systematic differences in shoot phosphorus (P) or organic-nitrogen (N) concentration between orders. At a species level, there were strong positive correlations between shoot Ca and Mg concentration, between shoot P and organic-N concentration, and between shoot K concentration and shoot fresh weight:dry weight ratio. Shoot C and cation concentration correlated negatively at a species level. Species within the Poales and the Caryophyllales had distinct shoot mineralogies in both the designed experiment and in the ecological survey.

Interactions between aboveground and belowground induction of glucosinolates in two wild Brassica species

Abstract: Summary • Interactions between shoot and root induction of glucosinolates in two crucifers, Brassica oleracea and B. nigra, were studied by applying the signalling hormones jasmonic acid (JA) and salicylic acid (SA). • JA application increased total shoot glucosinolate levels 1.5–3 times, but total root levels did not increase. Only root JA-application yielded a systemic response. In B. oleracea it mattered where JA was applied: root application increased aliphatic glucosinolates in the shoot, whereas shoot application increased indole glucosinolates. Plants treated with JA to both organs had profiles similar to shoot-treated plants. SA-application did not disturb the organ-specific response to JA. Increases in glucosinolate levels did not reduce plant biomass. • A applications reduced root glucosinolates in root-treated plants. SA root-application in B. nigra resulted in lesions on the leaves and shoot-application caused a trichome response. • lants thus respond specifically, depending on the organ that is induced and the hormone that is applied. We find a large potential for root-feeders to affect shoot-feeders. Glucosinolate induction in one organ is not constrained by induction in the other organ.

Impact of two fluorescent pseudomonads and an arbuscular mycorrhizal fungus on tomato plant growth, root architecture and P acquisition

Abstract: The ability of fluorescent pseudomonads and arbuscular mycorrhizal fungi (AMF) to promote plant growth is well documented but knowledge of the impact of pseudomonad-mycorrhiza mixed inocula on root architecture is scanty. In the present work, growth and root architecture of tomato plants (Lycopersicon esculentum Mill. cv. Guadalete), inoculated or not with Pseudomonas fluorescens 92rk and P190r and/or the AMF Glomus mosseae BEG12, were evaluated by measuring shoot and root fresh weight and by analysing morphometric parameters of the root system. The influence of the microorganisms on phosphorus (P) acquisition was assayed as total P accumulated in leaves of plants inoculated or not with the three microorganisms. The two bacterial strains and the AMF, alone or in combination, promoted plant growth. P. fluorescens 92rk and G. mosseae BEG12 when co-inoculated had a synergistic effect on root fresh weight. Moreover, co-inoculation of the three microorganisms synergistically increased plant growth compared with singly inoculated plants. Both the fluorescent pseudomonads and the myco-symbiont, depending on the inoculum combination, strongly affected root architecture. P. fluorescens 92rk increased mycorrhizal colonization, suggesting that this strain is a mycorrhization helper bacterium. Finally, the bacterial strains and the AMF, alone or in combination, improved plant mineral nutrition by increasing leaf P content. These results support the potential use of fluorescent pseudomonads and AMF as mixed inoculants for tomato and suggest that improved tomato growth could be related to the increase in P acquisition.

Effects of salt stress on plant growth, stomatal response and solute accumulation of different maize genotypes

Abstract: Seeds from eight different maize genotypes (BR3123, BR5004, BR5011, BR5026, BR5033, CMS50, D766 and ICI8447) were sown in vermiculite, and after germination they were transplanted into nutrient solution or nutrient solution containing 100 mmolL-1 of NaCl and placed in a greenhouse During the experimental period plant growth (dry matter, shoot to root dry mass ratio, leaf area, relative growth rate, and net assimilation rate), leaf temperature, stomatal conductance, transpiration, predawn water potential, sodium, potassium, soluble amino acids and soluble carbohydrate contents were determined in both control and salt stressed plants of all genotypes studied Salt stress reduced plant growth of all genotypes but the genotypes BR5033 and BR5011 were characterized as the most salt-tolerant and salt-sensitive, respectively Stomatal response of the salt-tolerant genotype was not affected by salinity Among the studied parameters, shoot to root dry mass ratio, leaf sodium content and leaf soluble organic solute content showed no relation with salt tolerance, ie, they could not be considered as good morpho-physiological markers for maize salt tolerance In contrast, sodium and soluble organic solutes accumulation in the roots as a result of salt stress appeared to play an important role in the acclimation to salt stress of the maize genotypes studied, suggesting that they could be used as physiological markers during the screening for salt tolerance

Thermotolerance of Pearl Millet and Maize at Early Growth Stages: Growth and Nutrient Relations

Abstract: Thermotolerance of pearl millet (Pennisetum glaucum cv. ICMV-94133) and maize (Zea mays cv. Golden) was assessed at germination and vegetative stage. Final percentage of germinated seeds and rate of germination (number of days to 50 % germination) decreased due to high temperature (45 °C) similarly in the both species. In contrast, at the vegetative stage, high temperature (38/27 °C) caused a significant reduction in shoot dry mass of maize, whereas this attribute remained almost unchanged in pearl millet. Relative growth rate and net assimilation rate (NAR) increased significantly in pearl millet due to high temperature, but in contrast, in maize NAR was slightly reduced. Concentrations of N, P, and K in the shoots of both species increased at high temperature, but N accumulation was more pronounced in pearl millet than in maize. High temperature caused a marked increase in both shoot and root Ca2+ concentration in maize, but it did not affect that of pearl millet. S concentration in the shoots of maize decreased significantly due to high temperature, whereas that in pearl millet remained unaffected. Shoot Na+ concentration of both species was not significantly affected by high temperature. High temperature caused a significant increase in uptake of N, P, and K+ in pearl millet, but the uptake of Ca2+, Mg2+, Na+ and S remained unaffected in this species. In contrast, in maize, a significant increase in uptake of K+ and Ca2+, and a decrease in uptake of N, S, Mg2+, and Na+ were found at high temperature. Overall, maize showed lower tolerance to high temperature compared with pearl millet.

Agrobacterium -mediated genetic transformation and development of herbicide-resistant sugarcane ( Saccharum species hybrids) using axillary buds

Abstract: Direct regeneration from explants without an intervening callus phase has several advantages, including production of true type progenies. Axillary bud explants from 6-month-old sugarcane cultivars Co92061 and Co671 were co-cultivated with Agrobacterium strains LBA4404 and EHA105 that harboured a binary vector pGA492 carrying neomycin phosphotransferase II, phosphinothricin acetyltransferase (bar) and an intron containing beta-glucuronidase (gus-intron) genes in the T-DNA region. A comparison of kanamycin, geneticin and phosphinothricin (PPT) selection showed that PPT (5.0 mg l(-1)) was the most effective selection agent for axillary bud transformation. Repeated proliferation of shoots in the selection medium eliminated chimeric transformants. Transgenic plants were generated in three different steps: (1) production of putative primary transgenic shoots in Murashige-Skoog (MS) liquid medium with 3.0 mg l(-1) 6-benzyladenine (BA) and 5.0 mg l(-1) PPT, (2) production of secondary transgenic shoots from the primary transgenic shoots by growing them in MS liquid medium with 2.0 mg l(-1) BA, 1.0 mg l(-1) kinetin (Kin), 0.5 mg l(-1) alpha-napthaleneacetic acid (NAA) and 5.0 mg l(-1) PPT for 3 weeks, followed by five more cycles of shoot proliferation and selection under same conditions, and (3) rooting of transgenic shoots on half-strength MS liquid medium with 0.5 mg l(-1) NAA and 5.0 mg l(-1) PPT. About 90% of the regenerated shoots rooted and 80% of them survived during acclimatisation in greenhouse. Transformation was confirmed by a histochemical beta-glucuronidase (GUS) assay and PCR amplification of the bar gene. Southern blot analysis indicated integration of the bar gene in two genomic locations in the majority of transformants. Transformation efficiency was influenced by the co-cultivation period, addition of the phenolic compound acetosyringone and the Agrobacterium strain. A 3-day co-cultivation with 50 micro M acetosyringone considerably increased the transformation efficiency. Agrobacterium strain EHA105 was more effective, producing twice the number of transgenic shoots than strain LBA4404 in both Co92061 and Co671 cultivars. Depending on the variety, 50-60% of the transgenic plants sprayed with BASTA (60 g l(-1) glufosinate) grew without any herbicide damage under greenhouse conditions. These results show that, with this protocol, generation and multiplication of transgenic shoots can be achieved in about 5 months with transformation efficiencies as high as 50%.

Physiological characterisation of magnesium deficiency in sugar beet: acclimation to low magnesium differentially affects photosystems I and II

Abstract: Magnesium deficiency in plants is a widespread problem, affecting productivity and quality in agriculture, yet at a physiological level it has been poorly studied in crop plants. Here, a physiological characterization of Mg deficiency in Beta vulgaris L., an important crop model, is presented. The impact of Mg deficiency on plant growth, mineral profile and photosynthetic activity was studied. The aerial biomass of plants decreased after 24 days of hydroponic culture in Mg-free nutrient solution, whereas the root biomass was unaffected. Analysis of mineral profiles revealed that Mg decreased more rapidly in roots than in shoots and that shoot Mg content could fall to 3 mg g−1 DW without chlorosis development and with no effect on photosynthetic parameters. Sucrose accumulated in most recently expanded leaves before any loss in photosynthetic activity. During the development of Mg deficiency, the two photosystems showed sharply contrasting responses. Data were consistent with a down-regulation of PSII through a loss of antenna, and of PSI primarily through a loss of reaction centres. In each case, the net result was a decrease in the overall rate of linear electron transport, preventing an excess of reductant being produced during conditions under which sucrose export away from mature leaf was restricted.

Growth, nitrogen fixation and ammonium assimilation in common bean (Phaseolus vulgaris): effect of phosphorus

Abstract: The impact of phosphorous nutrition on plant growth, symbiotic N 2 fixation, ammonium assimilation, carbohydrate and aminoacid accumulation, as well as on nitrogen, phosphorus and ATP content in tissues in common bean (Phaseolus vulgaris) plants was investigated. Plants inoculated with Rhizobium tropici CIAT899 were grown in Leonard jars under controlled conditions, with P-deficient (0 and 0.1 mM), P-medium (0.5, 1 and 1.5 mM) and P-high (2 mM) conditions in a N-free nutrient solution. The P application, increased leaf area, whole plant DW (67%), nodule biomass (4-fold), and shoot and root P content (4- and 6-fold, respectively) in plant harvested at the onset of flowering (28-days-old). However, P treatments decreased the total soluble sugar and amino acid content in vegetative organs (leaf, root and nodules). The root growth proved less sensitive to P deficiency than did shoot growth, and the leaf area was significantly reduced at low P-application. The absence of a relationship between shoot N content, and P levels in the growth medium could indicate that nitrogen fixation requires more P than does plant growth. The optimal amount for the P. vulgaris-R. tropici CIAT899 symbiosis was 1.5 mM P, this treatment augmented nodule-ARA 20-fold, and ARA per plant 70-fold compared with plants without P application.

Drought tolerance and transplanting performance of holm oak (Quercus ilex) seedlings after drought hardening in the nursery.

Abstract: Summary Drought stress is the main cause of mortality of holm oak (Quercus ilex L.) seedlings in forest plantations. We therefore assessed if drought hardening, applied in the nursery at the end of the growing season, enhanced the drought tolerance and transplanting performance of holm oak seedlings. Seedlings were subjected to three drought hardening intensities (low, moderate and severe) for 2.5 and 3.5 months, and compared with control seedlings. At the end of the hardening period, water relations, gas exchange and morphological attributes were determined, and survival and growth under mesic and xeric transplanting conditions were assessed. Drought hardening increased drought tolerance primarily by affecting physiological traits, with no effect on shoot/root ratio or specific leaf mass. Drought hardening reduced osmotic potential at saturation and at the turgor loss point, stomatal conductance, residual transpiration (RT) and new root growth capacity (RGC), but enhanced cell membrane stability. Among treated seedlings, the largest response occurred in seedlings subjected to moderate hardening. Severe hardening reduced shoot soluble sugar concentration and increased shoot starch concentration. Increasing the duration of hardening had no effect on water relations but reduced shoot mineral and starch concentrations. Variation in cell membrane stability, RT and RGC were negatively related to osmotic adjustment. Despite differences in drought tolerance, no differences in mortality and relative growth rate were observed between hardening treatments when the seedlings were transplanted under either mesic or xeric conditions.