Silicon improves salinity tolerance in wheat plants

Durum wheat (Triticum durum cv. Gediz-75) and bread wheat (Triticum aestivum cv. Izmir-85) were grown in a complete nutrient solution in a growth room to investigate effect of silicone supplied to the nutrient solution on plants grown at salt stress. The experiment was a 2 × 2 factorial arrangement with two levels of NaCl in nutrient solution, 0 and 100 mM, and two levels of silicone (Si) in nutrient solution, 0.25 and 0.50 mM, as Na₂SiO₃. The plants grown at 100 mM NaCl produced less dry matter and chlorophyll content than those without NaCl. Supplementary Si at both 0.25 and 0.5 mM ameliorated the negative effects of salinity on plant dry matter and chlorophyll content. Membrane permeability and proline content in leaves increased with addition of 100 mM NaCl and these increases were decreased with Si treatments. Sodium (Na) concentration in plant tissues increased in both leaves and roots of plants in the high NaCl treatment and Si treatments lowered significantly the concentrations of Na in both leaves and roots. Bread wheat was more tolerant to salinity than durum wheat. The accumulation of Na in roots indicates a possible mechanism whereby bread wheat copes with salinity in the rooting medium and/or may indicate the existence of an inhibition mechanism of Na transport to leaves. Concentrations of both Ca and K were lower in the plants grown at high NaCl than in those in the control treatment and these two element concentrations were increased by Si treatments in both shoots and roots but remained lower than control values in most cases.     

Enzymes of nitrogen assimilation in maize roots

The intracellular distribution of enzymes involved in the Crassulacean acid metabolism (CAM) has been studied in Bryophyllum calycinum Salisb. and Crassula lycopodioides Lam. After separation of cell organelles by isopycnic centrifugation, enzymes of the Crassulacean acid metabolism were found in the following cell fractions: Phosphoenolpyruvate carboxylase in the chloroplasts; NAD-dependent malate dehydrogenase in the mitochondria and in the supernatant; NADP-dependent malate dehydrogenase and phosphoenolpyruvate carboxykinase in the chloroplasts; NADP-dependent malic enzyme in the supernatant and to a minor extent in the chloroplasts; NAD-dependent malic enzyme in the supernatant and to some degree in the mitochondria; and pyruvate; orthophosphate dikinase in the chloroplasts. The activity of the NAD-dependent malate dehydrogenase was due to three isoenzymes separated by (NH₄)₂SO₄ gradient solubilization. These isoenzymes represented 17, 78, and 5% of the activity recovered, respectively, in the order of elution. The isoenzyme eluting first was associated with the mitochondria and the second isoenzyme was of cytosolic origin, while the intracellular location of the third isoenzyme was probably the peroxisome. Based on these findings, the metabolic path of Crassulacean acid metabolism within cells of CAM plants is discussed. New address: Institut für Pflanzenphysiologie und Zellbiologie, Freie Universität Berlin, Königin-Luise-Straße 12-16a. D-1000 Berlin 33     

Exogenous spermidine affects polyamine metabolism in salinity-stressed Cucumis sativus roots and enhances short-term salinity tolerance

We investigated the effects of short-term salinity stress and spermidine application to salinized nutrient solution on polyamine metabolism and various stress defense reactions in the roots of two cucumber (Cucumis sativus L.) cultivars, Changchun mici and Jinchun No. 2. Seedlings grown in nutrient solution salinized with 50 mM NaCl for 8 d displayed reduced relative water content, net photosynthetic rates and plant growth, together with increased lipid peroxidation and electrolyte leakage in the roots. These changes were more marked in cv. Jinchun No. 2 than in cv. Changchun mici, confirming that the latter cultivar is more salinity-tolerant than the former. Salinity stress caused an increase in superoxide and hydrogen peroxide production, particularly in cv. Jinchun No. 2 roots, while the salinity-induced increase in antioxidant enzyme activities and proline contents in the roots was much larger in cv. Changchun mici than in cv. Jinchun No. 2. In comparison to cv. Jinchun No. 2, cv. Changchun mici showed a marked increase in arginine decarboxylase, ornithine decarboxylase, S-adenosylmethionine decarboxylase and diamine oxidase activities, as well as free spermidine and spermine, soluble conjugated and insoluble bound putrescine, spermidine and spermine contents in the roots during exposure to salinity. On the other hand, spermidine application to salinized nutrient solution resulted in alleviation of the salinity-induced membrane damage in the roots and plant growth and photosynthesis inhibition, together with an increase in polyamine and proline contents and antioxidant enzyme activities in the roots of cv. Jinchun No. 2 but not of cv. Changchun mici. These results suggest that spermidine confers short-term salinity tolerance on cucumber probably through inducing antioxidant enzymes and osmoticants.     

Effect of light intensity on ammonia assimilation in maize leaves

The effect of light on the metabolism of ammonia was studied by subjecting detached maize leaves to 150 or 1350 mol m^–2 s^–1 PAR during incubation with the leaf base in 2 mM ¹⁵NH₄Cl. After up to 60 min, leaves were extracted. Ammonia, glutamine, glycine, serine, alanine, and aspartate were separated by isothermal distillation and ion exchange chromatography. ¹⁵N enrichments were analyzed by emission spectroscopy. The uptake of ammonium chloride did not influence CO₂ assimilation (8.3 and 17.4 mol m^–1 s^–1 at 150 and 1350 mol m^–2 s^–1 PAR, respectively). Leaves kept at high light intensity contained more serine and less alanine than leaves from low light treatments. Within 1 h of incubation the enrichment of ammonia extracted from leaves rose to approximately 20% ¹⁵N. In the high light regime the amino acids contained up to 15% ¹⁵N, whereas in low light ¹⁵N enrichments were small (up to 6%). The kinetics of ¹⁵N incorporation indicated that NH₃ was firstly assimilated into glutamine and then into glutamate. After 15 min ¹⁵N was also found in glycine, serine and alanine. At high light intensity nearly half of the ¹⁵N was incorporated in glycine. On the other hand, at low light intensity alanine was the predominant ¹⁵N sink. It is concluded that light influences ammonia assimilation at the glutamine synthetase reaction.     

Silicon supplementation improves drought tolerance in canola plants

This paper reports the effects of silicon (Si) supplementation (0.35 g Na₂SiO₃/kg soil, 2.73 mmol Si/kg soil) on some physiological characteristics of canola (Brassica napus L. cv. Okapi) plants grown in pots and treated with or without Si under water stress for 25 days. In this study, Si-supplied plants showed the higher shoot dry weight (SDW), root dry weight (RDW), relative growth rate (RGR), net assimilation rate (NAR), and relative water content (RWC) as compared to those without application of Si under drought conditions. However, Si did not significantly affect dry weight accumulation under well-watered conditions. CO₂ absorbance (A) was increased by silicon under water stress conditions. The intracellular CO₂ concentration (C _i), which was significantly elevated under water stress, was decreased by Si. Silicon application significantly increased the root amino acid content after 20 and 25 days of water stress. In Si-supplemented water-deficit plants, the amount of MDA remained unchanged after 25 days of water stress, obviously because of an efficient scavenging following significant enhancement of superoxide dismutase (SOD) and peroxidase (POD) activities. These results indicated that Si ameliorated growth reduction of drought-stressed canola plants, accompanied by an increase in the root water uptake through the formation of more fine roots and more amino acids as osmotica for supporting water uptake. The results of this study revealed that Si application alleviated water stress damages because of the higher water uptake, better photosynthetic rate, and the lowered lipid peroxidation in canola plants.     

Lanthanum improves salt tolerance of maize seedlings

In this study, the effects of lanthanum were investigated on contents of pigments, chlorophyll (Chl) fluorescence, antioxidative enzymes, and biomass of maize seedlings under salt stress. The results showed that salt stress significantly decreased the contents of Chl and carotenoids, maximum photochemical efficiency of PSII (F_v/F_m), photochemical quenching (q_P), and quantum efficiency of PSII photochemistry (Φ_PSII), net photosynthetic rate (P_N), and biomass. Salt stress increased nonphotochemical quenching (q_N), the activities of ascorbate peroxidase, catalase, superoxide dismutase, glutathione peroxidase, and the contents of malondialdehyde and hydrogen peroxide compared with control. Pretreatment with lanthanum prior to salt stress significantly enhanced the contents of Chl and carotenoids, F_v/F_m, q_P, q_N, Φ_PSII, P_N, biomass, and activities of the above antioxidant enzymes compared with the salt-stressed plants. Pretreatment with lanthanum also significantly reduced the contents of malondialdehyde and hydrogen peroxide induced by salt stress. Our results suggested that lanthanum can improve salt tolerance of maize seedlings by enhancing the function of photosynthetic apparatus and antioxidant capacity.     

Gibberellic acid improves water deficit tolerance in maize plants

The combination effects of water stress and gibberellic acid (GA₃) on physiological attributes and nutritional status of maize (Zea mays L. cv., DK 647 F1) were studied in a pot experiment. Maize plants were grown in the control (well watered WW) and water stress subjected to treated both water stress and two concentrations of gibberellic acid (GA₃ 25 mg L⁻¹, 50 mg L⁻¹). WS was imposed by maintaining the moisture level equivalent to 50 % pot capacity whereas the WW pots were maintained at full pot capacity. Water stress reduced the total dry weight, chlorophyll concentration, and leaf relative water content (RWC), but it increased proline accumulation and electrolyte leakage in maize plants and appears to affect shoots more than roots. Both concentrations of GA₃ (25 and 50 mg L⁻¹) largely enhanced the above physiological parameters to levels similar to control. WS reduced leaf Ca²⁺ and K⁺ concentrations, but exogenous application of GA₃ increased those nutrient levels similar or close to control. Exogenous application of GA₃ improved the water stress tolerance in maize plants by maintaining membrane permeability, enhancing chlorophyll concentration, leaf relative water content (LRWC) and some macro-nutrient concentrations in leaves.     

High irradiance improves ammonium tolerance in wheat plants by increasing N assimilation

Ammonium is a paradoxical nutrient ion. Despite being a common intermediate in plant metabolism whose oxidation state eliminates the need for its reduction in the plant cell, as occurs with nitrate, it can also result in toxicity symptoms. Several authors have reported that carbon enrichment in the root zone enhances the synthesis of carbon skeletons and, accordingly, increases the capacity for ammonium assimilation. In this work, we examined the hypothesis that increasing the photosynthetic photon flux density is a way to increase plant ammonium tolerance. Wheat plants were grown in a hydroponic system with two different N sources (10 mM nitrate or 10 mM ammonium) and with two different light intensity conditions (300 μmol photon m⁻² s⁻¹ and 700 μmol photon m⁻² s⁻¹). The results show that, with respect to biomass yield, photosynthetic rate, shoot:root ratio and the root N isotopic signature, wheat behaves as a sensitive species to ammonium nutrition at the low light intensity, while at the high intensity, its tolerance is improved. This improvement is a consequence of a higher ammonium assimilation rate, as reflected by the higher amounts of amino acids and protein accumulated mainly in the roots, which was supported by higher tricarboxylic acid cycle activity. Glutamate dehydrogenase was a key root enzyme involved in the tolerance to ammonium, while glutamine synthetase activity was low and might not be enough for its assimilation.     

Presoaking with hemin improves salinity tolerance during wheat seed germination

The aim of this study was to investigate whether presoaking with hemin, an inducer of heme oxygenase-1 (HO-1), could alleviate salinity damage during wheat seed germination in comparison with the pretreatment of a well-known nitric oxide (NO) donor sodium nitroprusside (SNP). The results showed that, compared with the samples upon 150 mM NaCl salt stress alone, both 10 ??M hemin and 200 ??M SNP pretreatments could (1) significantly attenuate the inhibition of seed germination and thereafter seedling growth; (2) induce HO expression; (3) enhance amylase activity, thus accelerating the formation of reducing sugar and total soluble sugar; and (4) increase the potassium (K) to sodium (Na) ratio, particularly in the shoot parts. Hemin and SNP could also increase antioxidant enzyme activities, including superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD), and ascorbate peroxidase (APX), thus resulting in the alleviation of oxidative damage, as indicated by the decrease of thiobarbituric acid reactive substances (TBARS) content. Moreover, semi-quantitative RT-PCR and isozymatic analysis illustrated that hemin and SNP pretreatment were able to up-regulate the expression of Mn-SOD (especially) and Cu/Zn-SOD gene, and activate SOD isozymatic activities. Since the addition of the NO scavenger methylene blue (MB) differentially reversed the above effects, the protective roles of hemin might be related to the induction of endogenous NO signal. Meanwhile, hemin-driven NO production was confirmed. Together, these results indicated that hemin exerted an advantageous effect on enhancing salinity tolerance during wheat seed germination, which might interact with NO.     

Paraburkholderia sp. GD17 improves rice seedling tolerance to salinity

Plant and Soil - A better knowledge of how deadwood decomposes is critical for accurately characterizing carbon and nutrient cycling in forests. Fungi dominate this decomposition process, but we...     

Engineering of enhanced glycine betaine synthesis improves drought tolerance in maize

Glycine betaine plays an important role in some plants, including maize, in conditions of abiotic stress, but different maize varieties vary in their capacity to accumulate glycine betaine. An elite maize inbred line DH4866 was transformed with the betA gene from Escherichia coli encoding choline dehydrogenase (EC 1.1.99.1), a key enzyme in the biosynthesis of glycine betaine from choline. The transgenic maize plants accumulated higher levels of glycine betaine and were more tolerant to drought stress than wild-type plants (non-transgenic) at germination and the young seedling stage. Most importantly, the grain yield of transgenic plants was significantly higher than that of wild-type plants after drought treatment. The enhanced glycine betaine accumulation in transgenic maize provides greater protection of the integrity of the cell membrane and greater activity of enzymes compared with wild-type plants in conditions of drought stress.     

Trehalose accumulation in Azospirillum brasilense improves drought tolerance and biomass in maize plants

Bacteria of the genus Azospirillum increase the grain yield of several grass crops. In this work the effect of inoculating maize plants with genetically engineered Azospirillum brasilense for trehalose biosynthesis was determined. Transformed bacteria with a plasmid harboring a trehalose biosynthesis gene-fusion from Saccharomyces cerevisiae were able to grow up to 0.5 M NaCl and to accumulate trehalose, whereas wild-type A. brasilense did not tolerate osmotic stress or accumulate significant levels of the disaccharide. Moreover, 85% of maize plants inoculated with transformed A. brasilense survived drought stress, in contrast with only 55% of plants inoculated with the wild-type strain. A 73% increase in biomass of maize plants inoculated with transformed A. brasilense compared with inoculation with the wild-type strain was found. In addition, there was a significant increase of leaf and root length in maize plants inoculated with transformed A. brasilense . Therefore, inoculation of maize plants with A. brasilense containing higher levels of trehalose confers drought tolerance and a significant increase in leaf and root biomass. This work opens the possibility that A. brasilense modified with a chimeric trehalose biosynthetic gene from yeast could increase the biomass, grain yield and stress tolerance in other relevant crops.     

Antisense suppression of proline degradation improves tolerance to freezing and salinity in Arabidopsis thaliana

The location of tryptophan residues in the actin macromolecule was studied on the basis of the known 3D structure. For every tryptophan residue the polarity and packing density of their microenvironments were evaluated. To estimate the accessibility of the tryptophan residues to the solvent molecules it was proposed to analyze the radial dependence of the packing density of atoms in the macromolecule about the geometric center of the indole rings of the tryptophan residues. The proposed analysis revealed that the microenvironment of tryptophan residues Trp-340 and Trp-356 has a very high density. So these residues can be regarded as internal and inaccessible to solvent molecules. Their microenvironment is mainly formed by non-polar groups of protein. Though the packing density of the Trp-86 microenvironment is lower, this tryptophan residue is apparently also inaccessible to solvent molecules, as it is located in the inner region of macromolecule. Tryptophan residue Trp-79 is external and accessible to the solvent. All residues that can affect tryptophan fluorescence were revealed. It was found that in the close vicinity of tryptophan residues Trp-79 and Trp-86 there are a number of sulfur atoms of cysteine and methionine residues that are known to be effective quenchers of tryptophan fluorescence. The most essential is the location of SG atom of Cys-10 near the NE1 atom of the indole ring of tryptophan residue Trp-86. On the basis of microenvironment analysis of these tryptophan residues and the evaluation of energy transfer between them it was concluded that the contribution of tryptophan residues Trp-79 and Trp-86 must be low. Intrinsic fluorescence of actin must be mainly determined by two other tryptophan residues--Trp-340 and Trp-356. It is possible that the unstrained conformation of tryptophan residue Trp-340 and the existence of aromatic rings of tyrosine and phenylalanine and proline residues in the microenvironments of tryptophan residues Trp-340 and Trp-356 are also essential to their blue fluorescence spectrum.     

Accumulation of terpenoid phytoalexins in maize roots is associated with drought tolerance

Maize (Zea mays) production, which is of global agro‐economic importance, is largely limited by herbivore pests, pathogens and environmental conditions, such as drought. Zealexins and kauralexins belong to two recently identified families of acidic terpenoid phytoalexins in maize that mediate defence against both pathogen and insect attacks in aboveground tissues. However, little is known about their function in belowground organs and their potential to counter abiotic stress. In this study, we show that zealexins and kauralexins accumulate in roots in response to both biotic and abiotic stress including, Diabrotica balteata herbivory, Fusarium verticillioides infection, drought and high salinity. We find that the quantity of drought‐induced phytoalexins is positively correlated with the root‐to‐shoot ratio of different maize varieties, and further demonstrate that mutant an2 plants deficient in kauralexin production are more sensitive to drought. The induction of phytoalexins in response to drought is root specific and does not influence phytoalexin levels aboveground; however, the accumulation of phytoalexins in one tissue may influence the induction capacity of other tissues.     

Nitrogen application improves gas exchange characteristics and chlorophyll fluorescence in maize hybrids under salinity conditions

The understanding of crop physiological responses to salinity stress is of paramount importance for selection of genotypes with improved tolerance to this stress. Maize (Zea mays L.) hybrids Pioneer 32B33 and Dekalb 979 were grown in pots and subjected to three levels of salinity under four nitrogen levels to determine the role of nitrogen under saline conditions. Salinity stress effects on gas exchange characteristics and chlorophyll fluorescence of maize hybrids were evaluated under semi-controlled conditions. Under salinity stress, the changes in the net photosynthetic rate (P _N), stomatal conductance (g _s), and transpiration rate (E) were similarly directed: all decreased and were lower than in control at the higher salinity level (10 dS/m). Water use efficiency was increased with increasing salinity since transpiration was stronger depressed by salt than photosynthesis. Plants subjected to the lower level of salinity did not differ from control in tested characteristics. Nitrogen application ameliorated the effects of salinity.     

Rapid synthesis of glutamine during the initial period of ammonia assimilation in roots of barley plants

After 1 hr of ammonia assimilation in barley plants, glutaminecontent in the roots increased 20 fold its original content,whereas contents of glutamic and aspartic acid decreased toa remarkable extent. These findings indicate a rapid synthesisof glutamine during the initial period of ammonia assimilationin roots. Results also suggest that glutamine synthesis fromglutamic acid initially occurring in the roots, is a primaryreaction of ammonia assimilation (Received May 11, 1971; )     

Early vertical distribution of roots and its association with drought tolerance in tropical maize

Background and aims

Selection for deep roots to improve drought tolerance of maize (Zea mays L.) requires presence of genetic variation and suitable screening methods.

Methods

We examined a diverse set of 33 tropical maize inbred lines that were grown in growth columns in the greenhouse up to the 2-, 4-, and 6-leaf stage and in the field in Mexico. To determine length of roots from different depths at high throughput, we tested an approach based on staining roots with methylene blue and measuring the amount of absorbed dye as proxy measure for root length.

Results

Staining provided no advantage over root weights that are much easier to measure and therefore preferable. We found significant genotypic variation for all traits at the 6-leaf stage. For development rates between the 2-leaf and the 6-leaf stage, genotypes only differed for rooting depth and the number of crown roots. Positive correlations of leaf area with root length and rooting depth indicated a common effect of plant vigor. However, leaf area in growth columns was negatively related to grain yield under drought (r?=??0.50).

Conclusion

The selection for deeper roots by an increase in plant vigor likely results in a poorer performance under drought conditions. The proportion of deep roots was independent of other traits but showed a low heritability and was not correlated to field performance. An improved screening protocol is proposed to increase throughput and heritability for this trait.

     

Bacterial inoculation of maize affects carbon allocation to roots and carbon turnover in the rhizosphere

To assess the influence of bacteria inoculation on carbon flow through maize plant and rhizosphere,¹⁴C allocation after¹⁴CO₂ application to shoots over a 5-day period was determined. Plants were grown on C- and N-free quartz sand in two-compartment pots, separating root and shoot space. While one treatment remained uninoculated, treatments two and three were inoculated withPantoea agglomerans (D5/23) andPseudomonas fluorescens (Ps I A12), respectively, five days after planting. Bacterial inoculation had profound impacts on carbon distribution within the system. Root/rhizosphere respiration was increased and more carbon was allocated to roots of plants being inoculated. After five days of¹⁴CO₂ application, more ethanol-soluble substances were found in roots of inoculated treatments and lower rhizodeposition indicated intensive C turnover in the rhizosphere. In both inoculated treatments the intensity of photosynthesis measured as net-CO₂-assimilation rates were increased when compared to the uninoculated plants. However, high C turnover in the rhizosphere reduced shoot growth of D5/23 inoculated plants, with no effect on shoot growth of Ps I A12 inoculated plants. A separation of labeled compounds in roots and rhizodeposition revealed that neutral substances (sugars) constituted the largest fraction. The relative fractions of sugars, amino acids and organic acids in roots and rhizodeposition suggest that amino acid exudation was particularly stimulated by bacterial inoculation and that turnover of this substance group is high in the rhizosphere.