Superoxide dismutase and total peroxidase activities in relation to drought recovery performance of mycorrhizal shrub seedlings grown in an amended semiarid soil

We studied the effect of inoculation with a mixture of three arbuscular mycorrhizal (AM) fungi (Glomus intraradices Schenck & Smith, Glomus deserticola (Trappe, Bloss. & Menge) and Glomus mosseae (Nicol & Gerd.) Gerd. & Trappe) and addition of a composted organic residue on plant growth, nutrient uptake, mycorrhizal colonisation and superoxide dismutase (SOD, EC 1.15.1.1) and total peroxidase (POX, EC 1.11.1.7) activities in shoots of Juniperus oxycedrus seedlings after well-watered, drought and recovery periods. The mycorrhizal inoculation and composted residue addition significantly increased the growth, foliar nutrients (N, P, K) and shoot water content of the plants, independent of the water regime. POX activity in control plants increased during drought (about 250% higher than under well-watered conditions) and returned to initial levels after re-watering. The seedlings inoculated with AM fungi showed the highest values of POX activity, followed by the plants grown in the amended soil, which varied little during the drought and recovery periods. Drought decreased the SOD activity in shoots of both J. oxycedrus seedlings inoculated with AM fungi and those grown with composted residue, but did not affect that of control plants. After re-watering, the SOD activity in mycorrhizal or residue-amended plants increased, showing values similar to control plants.     

Effect of Arbuscular Mycorrhizae and Induced Drought Stress on Antioxidant Enzyme and Nitrate Reductase Activities in Juniperus oxycedrus L. Grown in a Composted Sewage Sludge-amended Semi-arid Soil

We studied the influence of inoculation with a mixture of three exotic arbuscular mycorrhizal (AM) fungi, Glomus intraradices Schenck & Smith, Glomus deserticola Trappe, Bloss. & Menge and Glomus mosseae (Nicol & Gerd.) Gerd. & Trappe, and the addition of composted sewage sludge (SS) on the activities of the antioxidant enzymes superoxide dismutase (SOD, EC 1.15.1.1) and total peroxidase (POX) and of shoot and root nitrate reductase (NR, EC 1.6.6.1) in Juniperus oxycedrus L. seedlings, an evergreen shrub, grown in a non-sterile soil under well-watered and drought-stress conditions. Both the inoculation with exotic AM fungi and the addition of composted SS stimulated significantly growth and the N and P contents in shoot tissues of J. oxycedrus with respect to the plants neither inoculated nor treated with composted SS that were either well-watered or droughted. Under drought-stress conditions, only inoculation with exotic AM fungi increased shoot and root NR activity (about 188% and 38%, respectively, with respect to the plants neither inoculated nor treated with composted SS). Drought increased the POX and SOD activities in both shoots of J. oxycedrus seedlings inoculated with exotic AM fungi and grown with composted SS, but the increase was less than in the plants neither inoculated nor treated with SS. Both the plants inoculated with exotic AM fungi and the plants grown with composted SS developed additional mechanisms to avoid oxidative damage produced under water-shortage conditions.     

Epibrassinolide Application Regulates Some Key Physio-biochemical Attributes As Well As Oxidative Defense System in Maize Plants Grown Under Saline Stress

It was aimed to investigate the ameliorative effect of exogenously applied 24-epibrassinolide (EBR) on some key growth parameters and mineral elements in two salt-stressed maize (PR 32T83 and PR 34N24) cultivars. A factorial experiment was designed with two electrical permeability (EC) levels (1.1 and 8.0 dS/m) and two levels (1.5 and 2.0 µM) of EBR supplied as a seed treatment, foliar spray, or both in combination. The foliar application of EBR was done once a week during the experiment. After 42 days of these treatments, the plants were harvested to assess growth, water relations, and oxidative and antioxidative systems. Salt stress markedly reduced plant fresh and dry weights, maximum fluorescence yield of PS-II, chlorophyll contents, leaf water potential, and leaf K and Ca, but it increased membrane permeability, the activities of superoxide dismutase (SOD; EC 1.15.1.1), peroxidase (POD; EC. 1.11.1.7), and catalase (CAT; EC. 1.11.1.6) enzymes, and the contents of proline and glycine betaine, leaf sap osmotic pressure, lipid peroxidation, hydrogen peroxide, and leaf Na and Cl. However, both seed treatment and foliar application of EBR to the maize plants exposed to saline conditions enhanced key growth attributes, water relations, and the activities of various antioxidant enzymes as well as the levels of proline, but they reduced electrolyte leakage, and H₂O₂ and MDA contents. Saline stress reduced leaf N, Ca²⁺, K⁺, and P contents as compared to those in the non-stressed plants. Both seed treatment and foliar application of EBR reduced Na⁺ and Cl^? concentrations, but increased those of N, Ca²⁺, K⁺, and P. Foliar application of EBR was more effective in increasing nutrient levels of plants grown at the high saline regime compared to the seed treatment of EBR. The study clearly indicates that both seed treatment and foliar application of EBR at the rate of 2.0 µM can overcome the detrimental effect of salinity stress on maize growth, which was found to be significantly linked to reduced concentrations of Na, Cl, MDA, and H₂O₂ as well as EL and increased activities of key antioxidant enzymes in the maize plants.     

Improved Nutrient Use Efficiency Increases Plant Growth of Rice with the Use of IAA-Overproducing Strains of Endophytic Burkholderia cepacia Strain RRE25

Effect of indole acetic acid (IAA)-overproducing mutants of Burkholderia cepacia (RRE25), a member of β-subclass of Proteobacteria and naturally occurring rice endophyte, was observed on the growth of rice (Oryza sativa L.) plants grown under greenhouse conditions. Nine mutants were characterized for altered biosynthesis of IAA after nitrous acid mutagenesis. These mutants were grouped into two classes: class I mutants have reduced production of IAA as compared to the wild type, while class II mutants showed overproduction of IAA. Mutants of both classes and RRE25, the parent (wild type), were inoculated on rice seedlings of two cultivars (Sarjoo-52 and NDR-97). Uptake of nitrogen, phosphorous, and potassium was estimated in these plants. Significant increase in the amount of uptake of all three elements was observed when inoculated with the IAA-overproducing mutants over control as well as in the plants inoculated with the wild type (RRE25). Effect of inoculation of IAA-overproducing mutants was more pronounced on the uptake of phosphorous in cultivar NDR-97 than Sarjoo-52, while it was opposite with respect to potassium uptake. Any significant difference was not observed in nitrogen uptake among the two cultivars. It shows that the host also plays an important role in the beneficial endophytic association. It was concluded from these results that one of the possible mechanisms of growth promotion of rice plants inoculated with bacterial endophytes is their effects on an increase in the capability of nutritional uptake possible through the effect of IAA production which results in proliferation of root system that could mine more nutrients from the soil.     

Effects of applied nitrogen upon aspects of nitrogen metabolism and transport in developing nodulated winged bean plants

Nodulated winged bean [Psophocarpus tetragonolobus (L.) DC., cv. UPS 122] were grown under constant environmental conditions and supplied with mineral nutrient solution in which nitrogen was absent or was present as nitrate (12 mg N week^-1 plant^-1). Nitrate treatment dramatically promoted plant growth, increased fruit weight 1.6 fold, was necessary for tuberisation and enhanced nodulation. The in vitro accumulation of ¹⁴C into asparagine and aspartate components of excised nodules supplied with exogenous ¹⁴CO₂ and [¹⁴C]-D-glucose was greater for nitrate-treated plants, whilst accumulation into ureides was reduced by nitrate treatment. Levels of amino acids in xylem sap were greater for plants supplied with a complete nutrient solution, than those grown without applied nitrate, particularly for asparagine, glutamine and proline. Xylem ureide levels were greater for plants grown in the absence of supplementary nitrate. Nitrogen accumulated in leaf, stem and petiole, and root nodule tissues for utilisation during fruit development; peak nitrogen levels and time of anthesis were retarded for plants grown without applied nitrate. The shoot ureide content increased during fruiting, coincident with decreases in the total nitrogen content, indicating that ureide pools are not utilised during the early reproductive phase. However ureide reserves, particularly allantoin, were utilised during the later stages of pod fill. Enzyme activity which metabolised asparagine was found throughout the plant and was identified as K⁺-dependent asparaginase (EC 3.5.1.1) and an aminotransferase. Apart from temporal differences in developmental profiles of enzyme activity, the activity of these enzymes and of allantoinase (EC 3.5.2.5) in developing tissues were similar for both treatments. The main differences were greater asparaginase and asparagine:pyruvate aminotransferase activities in root tissues and fruit of nitrate-supplied plants; allantoinase activity in the primary roots of plants grown without nitrate decreased during development, whilst activity in developing tubers (nitrate-supplied plants) increased.     

Functional aspects of root architecture and mycorrhizal inoculation with respect to nutrient uptake capacity

The aim of this research was to investigate the effect of arbuscular mycorrhizal (AM) colonisation on root morphology and nitrogen uptake capacity of carob ( Ceratonia siliqua L.) under high and low nutrient conditions. The experimental design was a factorial arrangement of presence/absence of mycorrhizal fungus inoculation ( Glomus intraradices) and high/low nutrient status. Percent AM colonisation, nitrate and ammonium uptake capacity, and nitrogen and phosphorus contents were determined in 3-month-old seedlings. Grayscale and colour images were used to study root morphology and topology, and to assess the relation between root pigmentation and physiological activities. AM colonisation lead to a higher allocation of biomass to white and yellow parts of the root. Inorganic nitrogen uptake capacity per unit root length and nitrogen content were greatest in AM colonised plants grown under low nutrient conditions. A better match was found between plant nitrogen content and biomass accumulation, than between plant phosphorus content and biomass accumulation. It is suggested that the increase in nutrient uptake capacity of AM colonised roots is dependent both on changes in root morphology and physiological uptake potential. This study contributes to an understanding of the role of AM fungi and root morphology in plant nutrient uptake and shows that AM colonisation improves the nitrogen nutrition of plants, mainly when growing at low levels of nutrients.     

Ectomycorrhizal fungi enhance nitrogen and phosphorus nutrition of Nothofagus dombeyi under drought conditions by regulating assimilative enzyme activities

Drought stress conditions (DC) reduce plant growth and nutrition, restraining the sustainable reestablishment of Nothofagus dombeyi in temperate south Chilean forest ecosystems. Ectomycorrhizal symbioses have been documented to enhance plant nitrogen (N) and phosphorus (P) uptake under drought, but the regulation of involved assimilative enzymes remains unclear. We studied 1-year-old N. dombeyi (Mirb.) Oerst. plants in association with the ectomycorrhizal fungi Pisolithus tinctorius (Pers.) Coker & Couch. and Descolea antartica Sing. In greenhouse experiments, shoot and root dry weights, mycorrhizal colonization, foliar N and P concentrations, and root enzyme activities [glutamate synthase (glutamine oxoglutarate aminotransferase (GOGAT), EC 1.4.1.13-14), glutamine synthetase (GS, EC 6.3.1.2), glutamate dehydrogenase (GDH, EC 1.4.1.2-4), nitrate reductase (NR, EC 1.6.6.1), and acid phosphomonoesterase (PME, EC 3.1.3.1-2)] were determined as a function of soil-water content. Inoculation of N. dombeyi with P. tinctorius and D. antartica significantly stimulated plant growth and increased plant foliar N and P concentrations, especially under DC. Ectomycorrhizal inoculation increased the activity of all studied enzymes relative to non-mycorrhizal plants under drought. We speculate that GDH is a key enzyme involved in the enhancement of ectomycorrhizal carbon (C) availability by fuelling the tricarboxylic acid (TCA) cycle under conditions of drought-induced carbon deficit. All studied assimilative enzymes of the ectomycorrhizal associations, involved in C, N, and P transfers, are closely interlinked and interdependent. The up-regulation of assimilative enzyme activities by ectomycorrhizal fungal root colonizers acts as a functional mechanism to increase seedling endurance to drought. We insist upon incorporating ectomycorrhizal inoculation in existing Chilean afforestation programs.     

Effect of drought and low light on growth and enzymatic antioxidant system of Picea asperata seedlings

The combined effects of drought and low light on biomass partition, foliar nitrogen concentration, membrane stability and active oxygen species (AOS) and antioxidant system were investigated in dragon spruce (Picea asperata Mast.) seedlings grown at two watering regimes (well-watered, 100% of field capacity and drought, 30% of field capacity) and light availabilities (HL, 100% of full sunlight and low light, 15% of full sunlight). Under high light condition drought not only reduced foliar nitrogen concentration (Nmass) and membrane stability index (MSI) but also significantly increased biomass partitioning to roots, AOS, ascorbic acid (AsA) content and antioxidant enzyme activities including superoxide dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase(GR, EC 1.6.4.2). However, no prominently drought-induced differences in biomass partitioning to root, SOD, GR activities, hydrogen peroxide (H₂O₂) and MSI were observed in low light seedlings. On the other hand, significant interaction of drought and low light was found on MSI, the antioxidant enzymes activities (SOD, POD, CAT, APX, GR), H₂O₂ and superoxide radical (O₂ ⁻). These results suggested that seedlings grown at the understory were more sensitive to drought than low light.     

Effects of elevated [CO(2)] and nitrogen nutrition on cytokinins in the xylem sap and leaves of cotton

We measured the level of xylem-derived cytokinins (CKs) entering a cotton leaf, and the CK levels in the same leaf, thus enabling xylem sap and foliar CKs to be compared concurrently. Although zeatin was the dominant CK in xylem sap, zeatin, dihydrozeatin, and N(6)-(2-isopentenyl) adenine were present in approximately equimolar levels in leaves. Elevated [CO(2)] (EC) has an effect on the levels of cytokinins in sap and leaf tissues. This effect was modulated by the two levels of root nitrogen nutrition (2 and 12 mM nitrate). Growth enhancement (70%) in EC over plants in ambient [CO(2)] (AC) was observed for both nitrogen nutrition treatments. Low-nitrogen leaves growing in EC exhibited photosynthetic acclimation, whereas there was no sign of photosynthetic acclimation in high-nitrogen grown leaves. Under these prevailing conditions, xylem sap and leaf tissues were obtained for CK analysis. Higher nitrogen nutrition increased the delivery per unit leaf area of CKs to the leaf at AC. EC caused a greater increase in CK delivery to the leaf at low nitrogen conditions (106%) than at high nitrogen conditions (17%). EC induced a significant increase in CK content in low-nitrogen leaves, whereas CK content in leaf tissues was similar for high-nitrogen leaves growing in AC and EC.     

Effects of Stress Modifier Biostimulants on Vegetative Growth,Nutrients, and Antioxidants Contents of Garden Thyme (Thymus vulgaris L.) Under Water Deficit Conditions

The aim of this study is to investigate the effect of stress modulators on vegetative growth, antioxidants, and nutrient content of Thymus vulgaris L. under water deficit stress conditions. A factorial experiment was performed in the form of a randomized complete block design with 10 treatments and 3 replications in the 2019–2020 growing season. The factors were stress modulators at 5 levels (ZN: zinc nano-fertilizer, AA: amino acid, SW: seaweed, HA: humic acid and C: control) and irrigation regime at 2 levels [FIrr: full irrigation (100% field capacity) and DIrr: deficit irrigation (50% field capacity)]. The highest plant height, number of branches, and total dry weight of the garden thyme plant were observed in the foliar application of HA and SW under full irrigation conditions. Relative water content, chlorophyll a and b, and uptake of nutrients (N, P, and K) were reduced under water deficit stress, but the foliar application of stress modulators increased relative water content, chlorophyll content, and nutrient uptake of the garden thyme plant significantly compared with control. The water deficit increased proline content, total flavonoid, and phenol content in the garden thyme plant. So, the highest total flavonoid and phenol content was obtained from plants treated with HA, whereas proline content was higher in the control plants. Soluble sugars and essential oil increased significantly under water deficit stress conditions. The foliar application of HA compared to the control plant increased soluble sugars and essential oil in garden thymes. The activities of catalase, superoxide dismutase, and ascorbate peroxidase enzymes were improved in stress modulator treatments such as HA and SW compared to control plants under water deficit stress conditions. The plants of garden thymes showed a good response to stress modulator treatments under water stress conditions, and HA and SW treatments were found to be more effective.

     

Is resource allocation and grain yield of rice altered by inoculation with arbuscular mycorrhizal fungi?

Aims Our study quantified the combined effects of fertilization and inoculation with arbuscular mycorrhizal fungi (AMF) on grain yield and allocation of biomass and nutrients in field-grown rice (Oryza sativa L.).Methods A two-factor experiment was conducted at a field site in northeast of China (in Shuangcheng, Heilongjiang Province, Songhua River basin): six nitrogen–phosphorus–potassium fertilizer levels were provided (0, 20, 40, 60, 80 and 100% of the local norm of fertilizer supply), with or without inoculation with Glomus mosseae. At maturity, we quantified the percentage of root length colonization by AMF, grain yield, shoot:root ratios, shoot N and P contents and nutrients allocated to panicles, leaves and stems.Important findings As expected, inoculation resulted in greatly increased AMF colonization, which in turn led to higher shoot:root ratios and greater shoot N contents. Shoot:root ratios of inoculated rice increased with increasing fertilization while there was a significant interaction between fertilization and inoculation on shoot:root ratio. Additionally, AMF inoculation increased panicle:shoot ratios, panicle N:shoot N ratios and panicle P:shoot P ratios, especially in plants grown at low fertilizer levels. Importantly, inoculated rice exhibited higher grain yield, with the maximum improvement (near 62%) at the lower fertilizer end. Our results showed that (i) AMF-inoculated plants conform to the functional equilibrium theory, albeit to a reduced extent compared to non-inoculated plants and (ii) AMF inoculation resulted in greater allocation of shoot biomass to panicles and increased grain yield by stimulating N and P redistribution to panicles.     

Boron foliar supplementation as a strategy to attenuate drought stress in soybean

Drought is the major abiotic stress that limits growth, development and yield of crops worldwide. In this scenario, mineral nutrients, such as boron (B), have been promising for increasing the tolerance of plants to abiotic stresses because of their physiological roles in plants. We aimed to evaluate the benefits of foliar supplementation of B in either relieving or reducing the physiological damages caused by water stress in soybean (Glycine max L.). A greenhouse trial was carried out in a 2 × 3 factorial scheme, with two water conditions (well-watered and drought stress) and three doses of B (0, 150 and 300 mg B L⁻¹). Foliar application of B was before inducing the water stress, which remained for 20 days during vegetative stage. Plants were evaluated at three moments, according to the water conditions: maximum stress, rehydration and just before harvesting. The levels of hydrogen peroxide and lipid peroxidation increased in soybean leaves and roots under water stress, resulting in impaired plant growth. However, the foliar supplementation with B before the stress increased activities of the antioxidant enzymes and reduced the levels of stress markers. Furthermore, B applied foliar increased the nutrient concentration in the leaves of plants and stimulated root growth, which resulted in higher harvest index related to yield. The foliar application of B has shown as an alternative management to mitigate the damages caused by drought stress in soybean.     

Influence of Thiourea on Photosynthesis, Nitrogen Metabolism and Yield of Clusterbean (Cyamopsis tetragonoloba (L.) Taub.) under Rainfed Conditions of Indian Arid Zone

A 2-year field trial was conducted to study the effects of seed treatment (500 ppm) or foliar application of 1000 ppm thiourea (at 25 and 40 days after sowing) or a combination of these, on growth, yield, net photosynthesis and nitrogen metabolism of clusterbean (Cyamopsis tetragonoloba (L.) Taub.) grown for two consecutive years (1999 and 2000) under rainfed conditions of the Indian arid zone. Thiourea application either as pre-sowing seed treatment or as foliar spray significantly increased plant height, leaf area, dry matter production and seed yield as compared to the untreated control plants during both the years. However, maximum favourable effects were obtained with combined application of seed treatment and foliar spray. The beneficial effects of thiourea were attributed to its role in significantly increasing the net photosynthetic rates and the concentrations of total chlorophyll and starch in the leaves. Thiourea also reflected a positive role in enhancing nitrogen metabolism as it significantly increased nitrate reductase activity and concentration of soluble protein in the treated plants. It has been concluded that seed treatment with thiourea followed by foliar spray could significantly improve growth, yield and water use efficiency of rainfed clusterbean under arid conditions due to enhanced photosynthesis and more efficient nitrogen metabolism.     

Alleviation of salinity stress in broccoli using foliar urea or methyl-jasmonate: analysis of growth,gas exchange,and isotope composition

We studied the effects of foliar application of urea or methyl-jasmonate (MeJA) on the salinity tolerance of broccoli plants (Brassisca oleracea L. var. italica). Plant dry weight, leaf CO₂ assimilation, and root respiration were reduced significantly under moderate saline stress (40 mM NaCl) but application of either urea or MeJA maintained growth, gas exchange parameters, and leaf N–NO₃ ⁻ concentrations at values similar to those of non-salinized plants. Additionally, when these two foliar treatments were applied leaf Na⁺ concentration was reduced compared with control plants grown at 40 mM NaCl. However, at a higher salt concentration (120 mM NaCl), no effect of the foliar applications was found on these parameters. Salinity also decreased leaf δ¹⁵N but increased δ¹³C. Our study shows the feasibility of using foliar urea or MeJA to improve tolerance under moderate saline stress.     

The modes of action of two benzimidazoles and thiophanate-methyl used for the control of Verticillium wilt of strawberry

Benomyl, thiabendazole and thiophanate-methyl were found to be fungistatic against Verticillium dahliae in vitro. All materials suppressed wilt symptoms on artificially inoculated strawberry plants when applied as a root dip, soil drench or a foliar application. Quantitative bioassays of the amount of toxic residues and fungal colonization in tissues of treated plants after root treatment revealed that these materials or their toxic breakdown products were readily translocated to crown and leaves: they suppressed the internal spread of the pathogen throughout the plant. After foliar application there was no marked basipetal movement of material within the plant: fungal colonization was greatly reduced in treated leaves, but the roots and crowns were colonized to a similar extent to those of untreated plants.     

Detection of quantitative trait loci for seminal root traits in maize (Zea mays L.) seedlings grown under differential phosphorus levels

Suboptimal phosphorus availability is a primary constraint for terrestrial plant growth. Seminal roots play an important role in acquisition of nutrients by plant seedlings. The length and number of seminal roots may be particularly important in acquisition of immobile nutrients such as phosphorus by increasing soil exploration. The objective of this study was to identify quantitative trait loci (QTL) controlling seminal root growth in response to phosphorus stress in maize, and to characterize epistatic interactions among QTL. Seminal root length and number were evaluated in 162 recombinant inbred lines derived from a cross between B73 and Mo17 in seedlings grown in a controlled environment. B73 and Mo17 significantly differed for seminal root length under low phosphorus, but not under adequate phosphorus conditions. Seminal root length of the population grown under low phosphorus ranged from 0 to 79.2 cm with a mean of 32.3 cm; while seminal root length of plants grown under high phosphorus ranged from 0.67 to 59.0 cm with a mean of 23.4 cm. Under low phosphorus, one main-effect QTL was associated with seminal root length and three QTL with seminal root number; under high phosphorus, two QTL with seminal root length and three QTL for seminal root number. These accounted for 11, 25.4, 22.8, and 24.1% of the phenotypic variations for seminal root length and number at low phosphorus, and seminal root length and number at high phosphorus, respectively. Di-genic epistatic loci were detected for seminal root length at low phosphorus (two pairs) seminal root number at low phosphorus (eight pairs), seminal root length at high phosphorus (four pairs), and seminal root number at high phosphorus (two pairs), which accounted for 23.2, 50.6, 32.2, and 20.3% of the total variations, respectively. Seminal root traits observed here were positively yet weakly correlated with shoot biomass in the field under low phosphorus, although no coincident QTL were detected. These results suggest that epistatic interactions are important in controlling genotypic variation associated with seedling seminal root traits.     

Root zone calcium modulates the response of potato plants to heat stress

Potato plant growth and development are known to be severely impacted by heat stress. Here plants grown in a chemically inert medium of 1 : 1 quartzite : perlite (v : v) were subjected to either 35/25°C (stress) or 20/15°C (control) day/night air temperatures and four concentrations of root zone calcium (5, 25, 125 and 600 µ M Ca) for 3 weeks. We report for the first time that potato plant growth under heat stress can persist at specific levels of Ca²⁺ in the root zone and that the Ca²⁺ level required for growth under heat stress exceeds that required for growth under normal temperatures. We also provide strong, initial evidence that the ability of high Ca²⁺ levels to mitigate heat stress effects results from shifts in meristematic activity. Total foliar mass and leaf area were essentially unaffected by Ca²⁺ level under control temperatures. Under heat stress, leaf area was reduced to about 5% of the control at 5 and 25 µ M Ca but to only 70% of the control at 125 and 600 µ M Ca. Likewise, total foliar mass was reduced under heat stress to about 30% of the control at 5 and 25 µ M Ca but total foliar mass was greater under heat stress than control conditions at 125 and 600 µ M Ca. This increase at higher Ca²⁺ concentrations was due primarily to axillary shoot growth. Anatomical studies of leaves grown under heat stress show that cell expansion was impaired by heat stress and this impairment was overcome by increasing root zone calcium levels. These results provide insight into the mechanism by which root zone Ca²⁺ may modulate plant response to heat stress.     

Genotypic variation of nodules’ enzymatic activities in symbiotic nitrogen fixation among common bean (Phaseolus vulgaris L.) genotypes grown under salinity constraint

The effect of salt stress, under glasshouse conditions, was studied on plant biomass, nodulation, and activities of acid phosphatases (APase, EC 3.1.3.2) and trehalose 6-phosphate phosphatase (TPP, EC 3.1.3.12) in the symbiosis common bean (Phaseolus vulgaris L.)-rhizobia nodules. Four common bean recombinant inbred lines (147, 115, 104 and 83) were separately inoculated, with CIAT 899 or RhM11 strains and grown in hydroaeroponic culture. Two NaCl levels (0 and 25 mM NaCl plant^?1 week^?1 corresponding, respectively, to the control and the salt treatment) were applied and the culture was assessed during 42 days after their transplantation. The results showed that the nodulation of these lines was not affected by salinity except for the line 83 inoculated with CIAT 899, whose nodule dry weight decreased by 48.24 % compared with the corresponding controls. For the other symbiotic combinations, shoot and root biomasses were not significantly affected by salt constraint. Salinity stress generally reduced acid phosphatise and trehalose phosphate phosphatase activities in nodules that were less affected in plants inoculated with RhM11. Based on our data, it appears that nodule phosphatase activity may be involved in salinity tolerance in common beans and the levels of salt tolerance depend principally on specific combination of the rhizobial strain and the host cultivar.     

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

The impact of phosphorous nutrition on plant growth, symbiotic N₂ fixation, ammonium assimilation, carbohydrate and amino-acid 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 m M ), P-medium (0.5, 1 and 1.5 m M ) and P-high (2 m M ) 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 m M P, this treatment augmented nodule-ARA 20-fold, and ARA per plant 70-fold compared with plants without P application.