Reduced Nitrate Reductase Activity Research Articles

Synergistic influence of selenium and silicon supplementation prevents the oxidative effects of arsenic stress in wheat

Influence of supplementation of selenium (Se, 1 and 5 µM) and silicon (Si, 0.1 and 0.5 mM) was investigated in wheat under arsenic (30 µM As) stress. Plants grown under As stress exhibited a significant decline in growth parameters however, Se and Si supplementation mitigated the decline significantly. Treatment of Se and Si alleviated the reduction in the intermediate components of chlorophyll biosynthesis pathway and the content of photosynthetic pigments. Arsenic stressed plants exhibited increased reactive oxygen species accumulation and the NADPH oxidase activity which were lowered significantly due to Se and Si treatments. Moreover, Se and Si supplementation reduced lipid peroxidation and activity of lipoxygenase and protease under As stress. Supplementation of Se and Si significantly improved the antioxidant activities and the content of cysteine, tocopherol, reduced glutathione and ascorbic acid. Treatment of Se and Si alleviated the reduction in nitrate reductase activity. Exogenously applied Se and Si mitigated the reduction in mineral elements and reduced As accumulation. Hence, supplementation of Se and Si is beneficial in preventing the alterations in growth and metabolism of wheat under As stress.

BIOCHEMICAL CHANGES IN LEAVES OF RESISTANT AND SUSCEPTIBLE URDBEAN GENOTYPES INFECTED WITH URDBEAN LEAF CRINKLE VIRUS (ULCV)

Urdbean leaf crinkle virus (ULCV) is a widespread and most destructive virus that causes leaf crinkle disease in black gram. Virus infection causes alteration in physiological and biochemical processes within the plant. In present study, effect of viral infection was investigated on chlorophyll content, total soluble sugar, total protein, phenolic contents, sodium dismutase (SOD) and nitrate reductase activities in the leaves of susceptible and resistant genotypes of urdbean at 30 days after virus inoculation. Disease symptoms were mild (6.7% to 10%) in resistant genotypes and severe (36% to 43%) in susceptible genotypes. ULCV infection resulted in a significant decrease in chlorophyll content in infected plants of all genotypes over control plants; however, magnitude of reduction was more in susceptible genotypes (41%) as compared to the resistant genotypes (14.35%). The total sugar and protein contents were significantly higher in the inoculated susceptible (210.26 % and 68.67%, respectively) as compared to the resistant genotypes (183.87% and 25.89%, respectively). Also, the total phenolic content was significantly higher in inoculated resistant genotypes (83.91%) over the susceptible genotypes (25.89%). There was significant decrease in the activity of superoxide dismutase enzyme in resistant genotypes as compared to susceptible inoculated genotypes. Similarly, a reduction in nitrate reductase activity was more in inoculated plants of resistant genotypes. Our results indicate that post-infection significant increases in total sugars and proteins in susceptible genotypes and phenols in resistant genotypes may have a role in disease resistance and development. Changes in enzymatic activities in resistant and susceptible genotypes might also have some role in resistance against ULCV.

Alleviating excess boron stress in tomato calli by applying benzoic acid to various biochemical strategies

Benzoic acid (BA) represents vital roles in plant activity and response to diverse unfavorable conditions. However, its participation in mitigating excess boron (EB) stress in plants is elusive. Herein, we have examined the impacts of BA (1 μM) in controlling boron (B) uptake in tomato (Solanum lycopersicum L.) calli exposed to various EB levels (0, 1, 2, and 3 mM). The free, semi-bound, and bound B forms were stimulated by EB, while these forms were reduced in B-stressed calli by BA supplementation (40.37%, 36.08%, and 66.91%, respectively, less than 3 mM B-stressed calli alone). EB caused a reduction in the uptake of potassium (K+), calcium (Ca2+), magnesium (Mg2+), and nitrite (NO2−) while increasing the concentration of phosphorus (P), nitrate (NO3−), sulfur (S), and sulfate (SO42−) in B-stressed calli. BA application induced the uptake of K+, Ca2+, Mg2+, NO3−, S, and SO42−; however, it reduced P and NO2− concentrations in B-stressed calli. EB reduced nitrate reductase activity (NR), while BA application did not alleviate this reduction. EB treatments significantly, in most cases, increased sulfite oxidase (SO) activity. Supplementation of BA along with EB further enhanced SO activity. Cell wall components (cellulose, hemicellulose, and pectin) were decreased under EB treatments but considerably increased in B-stressed calli by BA application. Fourier Transform Infrared Spectrometer (FT-IR) output showed that EB treatments with/without BA led to alterations in cell wall functional groups of calli. Our findings indicated that BA application enabled tomato callus to counteract the harmful effect of EB, leading to improved callus growth.

Transcript profiling of stress‐responsive genes and metabolic changes during salinity in indica and japonica rice exhibit distinct varietal difference

In the present study, we carried out comprehensive transcriptional profiling of diverse genes under salinity (200 mM NaCl) at different time points, accompanied by certain biochemical alterations of the indica (IR-64 and Pokkali) and japonica (Nipponbare and M-202) rice. The higher susceptibility of Nipponbare and IR-64 was reflected by lower relative water content, chlorophyll loss, higher malondialdehyde content and accumulation of H2 O2 , and reduced nitrate reductase activity, compared to M-202 and Pokkali, where such changes were less pronounced. Enhanced levels of anthocyanins and reduced glutathione, together with elevated phenylalanine ammonia lyase activity, mainly conferred protection to Nipponbare and IR-64, while metabolites like phenolics, flavonoids, proline and polyamines were more induced in M-202 and Pokkali. Varietal differences in the expression pattern of diverse groups of genes to different durations (6, 24 and 48 h) of stress were striking. A gene showing early induction for a particular variety exhibited a delayed induction in another variety or a gradually decreased expression with treatment time. Pokkali was clearly identified as the salt-tolerant genotype among the test varieties based on increased antioxidant potential and enhanced expression of genes encoding for PAL, CHS and membrane transporters like SOS3, NHX-1 and HKT-1. The results presented in this work provide insight into the complex varying regulation patterns for different genes across the investigated rice varieties in providing salt tolerance and highlights distinct differences in expression patterns between susceptible and tolerant indica and japonica rice. This article is protected by copyright. All rights reserved.

Barley transcription factor HvNLP2 mediates nitrate signaling and affects nitrogen use efficiency.

Plants have evolved complex mechanisms to adapt to the changing nitrogen levels in the environment. In Arabidopsis, more than a dozen nitrate signaling regulatory genes have been characterized, including the NODULE INCEPTION-LIKE PROTEIN (AtNLP) genes, which play essential roles in nitrate signaling. However, whether NLP genes in the Triticeae crops are involved in nitrate regulation and nitrogen use efficiency (NUE) remains unknown. Here, we isolated a barley (Hordeum vulgare L.) mutant, hvnlp2-1, from a TILLING (Targeting Local Lesions IN Genomes) population and constructed two RNAi lines, hvnlp2-2 and hvnlp2-3, to study the function of HvNLP2. The expression of the nitrate-responsive genes was substantially inhibited after nitrate treatment in the hvnlp2 mutants, indicating that HvNLP2 controls nitrate signaling. Nitrate content was significantly higher in the hvnlp2 mutants, which may result from the decreased assimilation of nitrogen caused by reduced nitrate reductase activity and expression of nitrate assimilatory genes. HvNLP2 is localized to the nucleus in the presence of nitrate. Further investigation showed that HvNLP2 binds to and activates the nitrate-responsive cis-elements. Moreover, hvnlp2 exhibited reduced biomass, seed yield, and NUE. Therefore, HvNLP2 controls nitrate signaling and plays an important role in NUE.

Exogenously applied spermidine confers protection against cinnamic acid-mediated oxidative stress in Pisum sativum.

This study investigated the stress responses of cinnamic acid (CA) in pea plants and explored the protective role of spermidine (SPD) against CA-induced adverse effects. Pea seedlings exposed to CA had reduced length, biomass, moisture, chlorophyll, sugar, and protein contents and reduced nitrate reductase activity. These parameters increased when SPD was applied alone and in combination with CA. Electrolyte leakage and malondialdehyde content were high in seedlings treated with CA but decreased when the SPD+CA treatment was applied. Foliar exposure to SPD partially mitigated CA-induced stress effects by strengthening the antioxidant defense system, which helped preserve the integrity of biochemical processes. These results indicate that SPD (1mM) could mitigate the adverse effects of CA and enhance plant defense system. Hence, SPD can be used as a growth regulator for the maintenance of physiological functions in pea plants in response to the pernicious consequences of CA stress.

Nitrate Reductase Inhibition Induces Lipid Enhancement of Dunaliella Tertiolecta for Biodiesel Production.

Nitrogen stress increases lipids content in microalgae, the main feedstock for algal biodiesel. Sodium tungstate was used in this study to implement nitrogen stress by inhibiting nitrate reductase (NR) in Dunaliella tertiolecta. The reduction of NR activity was accompanied by reduction of chlorophyll and accumulation of lipids. One-stage and two-stage culture strategies were compared. One-stage culture raised total lipids from 18% (control) to 39% (w: w); however, two-stage culture raised lipids to 50% in which neutral lipids were enhanced 2.14 times. To assess the quality of biodiesel produced, fatty acid methyl esters (FAME) composition was studied. It showed a slight variation of unsaturation. In addition, some physical proprieties of biodiesel were estimated and showed that higher heating values were improved by tungstate treatment. In this study, we tried to shed light on some biological impact of NR inhibition in microalgae cells using sodium tungstate which could be exploited in the improvement of biodiesel production.

Ocean acidification and nutrient limitation synergistically reduce growth and photosynthetic performances of a green tide alga <i>Ulva linza</i>

Abstract. Large-scale green tides have been invading the coastal zones of the western Yellow Sea annually since 2008. Meanwhile, oceans are becoming more acidic due to continuous absorption of anthropogenic carbon dioxide, and intensive seaweed cultivation in Chinese coastal areas is leading to severe regional nutrient limitation. However, little is known about the combined effects of global and local stressors on the eco-physiology of bloom-forming algae. We cultured Ulva linza for 9–16 days under two levels of pCO2 (400 and 1000 µatm) and four treatments of nutrients (nutrient repletion, N limitation, P limitation, and N–P limitation) to investigate the physiological responses of this green tide alga to the combination of ocean acidification and nutrient limitation. For both sporelings and adult plants, elevated pCO2 did not affect the growth rate when cultured under nutrient-replete conditions but reduced it under P limitation; N or P limitations by themselves reduced growth rate. P limitation resulted in a larger inhibition in growth for sporelings compared to adult plants. Sporelings under P limitation did not reach the mature stage after 16 days of culture while those under P repletion became mature by day 11. Elevated pCO2 reduced net photosynthetic rate for all nutrient treatments but increased nitrate reductase activity and soluble protein content under P-replete conditions. N or P limitation reduced nitrate reductase activity and soluble protein content. These findings indicate that ocean acidification and nutrient limitation would synergistically reduce the growth of Ulva species and may thus hinder the occurrence of green tides in a future ocean environment.

Effect of N application on its utilization and gaseous exchange in cat tail (Typha elephantina) under waterlogged condition

The cat tail (Typha elephantina), a non-food commercial crop grows as an emergent hydrophyte in tidal waterlogged areas. Its leaves are used for preparing mats and used as roof top and wall partition. Typha sp. has been found to be efficient accumulator of N from sediment under waterlogged condition. The N utilization mainly through nitrate reductase (NR) activity was studied in Typha with four levels of N fertilizers i.e. 0, 30 and 60 and 90 kg ha−1 applied at three stages of plant growth i.e. basal, 3 and 6 month after planting. In general, there was reduction in NR activity under waterlogged condition in Typha. But application of @ 90 kg ha−1 maintained high NR activity when it was applied as basal stage. Basal application of N was found better than its application at 3 or 6 month stage of crop growth. The higher leaf NR activity at 60 and 90 kg ha−1 N application level suggested better N utilization under waterlogged environment. The photosynthesis rate showed significant increase with higher N application concomitant with greater stomatal conductance (r = 0.84**; n = 12). There was significant increase in leaf yield when N was applied @ 90 kg ha−1 N level as basal dosage as compared to later stage (3 or 6 months) of crop growth. The highest fertilizer use efficiency (kg dry leaf kg−1 applied N) was also found at 90 kg N ha−1 as compared to 30 or 60 kg ha−1 N level, which corroborated superior N fertilizer utilization ability of Typha under waterlogged condition.

Balancing of B6 Vitamers Is Essential for Plant Development and Metabolism in Arabidopsis.

Vitamin B6 comprises a family of compounds that is essential for all organisms, most notable among which is the cofactor pyridoxal 5'-phosphate (PLP). Other forms of vitamin B6 include pyridoxamine 5'-phosphate (PMP), pyridoxine 5'-phosphate (PNP), and the corresponding nonphosphorylated derivatives. While plants can biosynthesize PLP de novo, they also have salvage pathways that serve to interconvert the different vitamers. The selective contribution of these various pathways to cellular vitamin B6 homeostasis in plants is not fully understood. Although biosynthesis de novo has been extensively characterized, the salvage pathways have received comparatively little attention in plants. Here, we show that the PMP/PNP oxidase PDX3 is essential for balancing B6 vitamer levels in Arabidopsis thaliana. In the absence of PDX3, growth and development are impaired and the metabolite profile is altered. Surprisingly, RNA sequencing reveals strong induction of stress-related genes in pdx3, particularly those associated with biotic stress that coincides with an increase in salicylic acid levels. Intriguingly, exogenous ammonium rescues the growth and developmental phenotype in line with a severe reduction in nitrate reductase activity that may be due to the overaccumulation of PMP in pdx3. Our analyses demonstrate an important link between vitamin B6 homeostasis and nitrogen metabolism.

Effect of Nursery Nutrient Management on Plant Survival, Physiological Traits and Yield of Rice (Oryza sativa) Genotype Swarna-Sub1 Under Submerged Rainfed Lowland Ecosystem

An experiment was conducted to characterize nursery nutrient management by assessing morpho-physiological traits and yield attributes at different crop growth stages for improving submergence tolerance in Swarna-Sub1, a mega rice cultivar for Southeast Asia. Seven nutrient treatment combinations were applied at two different stages, one at after 10-day seeding and second at the time of transplanting (25-day-old seedlings) in cemented submergence tank. Fifteen days after transplanting, the plants were submerged for 13 days. Maximum plant height after submergence and at recovery was observed with T5 (N0:P0:K40). In leaves, ‘N,’ ‘P’ and ‘K’ content was highest in T1 (N40:P40:K40) followed by T6 (N0:P60:K40) and then with T3 (N0:P40:K40), respectively, at all crop growth stages studied. Highest seedling/plant dry weight before submergence and after submergence was recorded for T3 (N0:P40:K40) and T5 (N0:P0:K40). Submergence treatments significantly reduced nitrate reductase activity in leaves in all treatments. Maximum panicle length, panicle weight/hill, grain per panicle and biomass/hill were obtained in T6—N0:P60:K40. Positive correlation was found between survival and potassium content of shoot (r = 0.90**) followed by shoot total soluble sugar (TSS) (r = 0.52**). The finding of this experiment may be of use for balanced application of nutrient for improving submergence tolerance in rice.

Establishment of the forward genetic analysis of the chlorophyll d-dominated cyanobacterium Acaryochloris marina MBIC 11017 by applying in vivo transposon mutagenesis system.

Acaryochloris marina MBIC 11017 possesses chlorophyll (Chl) d as a major Chl, which enables this organism to utilize far-red light for photosynthesis. Thus, the adaptation mechanism of far-red light utilization, including Chl d biosynthesis, has received much attention, though a limited number of reports on this subject have been published. To identify genes responsible for Chl d biosynthesis and adaptation to far-red light, molecular genetic analysis of A. marina was required. We developed a transformation system for A. marina and introduced expression vectors into A. marina. In this study, the high-frequency in vivo transposon mutagenesis system recently established by us was applied to A. marina. As a result, we obtained mutants with the transposon in their genomic DNA at various positions. By screening transposon-tagged mutants, we isolated a mutant (Y1 mutant) that formed a yellow colony on agar medium. In the Y1 mutant, the transposon was inserted into the gene encoding molybdenum cofactor biosynthesis protein A (MoaA). The Y1 mutant was functionally complemented by introducing the moaA gene or increasing the ammonium ion in the medium. These results indicate that the mutation of the moaA gene reduced nitrate reductase activity, which requires molybdenum cofactor, in the Y1 mutant. This is the first successful forward genetic analysis of A. marina, which will lead to the identification of genes responsible for adaptation to far-red light.

Characterization of Tolerance Limit in Spirulina platensis in Relation to Nanoparticles

A study was carried out under in vitro condi- tions to characterize the growth of blue green alga, Spiru- lina platensis, in standard CFTRI medium containing dif- ferent nanoparticles of copper oxide (CuO) (50 nm, 10 ppm), zinc oxide (ZnO) (50 nm, 10 ppm), tricalcium phosphate (TCP) (<100 nm, 90 ppm), and hydroxy apatite (HA) (<200 nm, 90 ppm). S.platensisexhibited significant higher growth in standard CFTRI medium containing 90 ppm phosphorus as nanoparticles of TCP and HA. On the other hand, calcium phosphate nanoparticles caused significant reduction in nitrate reductase activity as well as in protein content of the alga. Marked change in chlorophyll-a/b ratio was also noted when phosphorus was supplied through nano tricalcium phosphate and nano hydroxy apatite particles as compared to ionic form (K2HPO4). The study revealed that the growth of Spirulina in the presence of ZnO nanoparticles was retarded, while no growth was observed with CuO nanoparticles. It was concluded that alga Spirulina showed much sensitivity to nanoparticles of zinc and copper (<50 nm) and was able to tolerate the toxicity of nanophosphate (tricalcium phos- phate <100 nm; hydroxy apatite <200 nm).

Effects of Copper Stress on Nitrogen Metabolism in Metallicolous and Non-Metallicolous Populations of &lt;i&gt;Rumex dentatus &lt;/i&gt;L&lt;i&gt;.&lt;/i&gt;

Two Rumex dentatus populations, one from copper (Cu) mine and the other from uncontaminated site, were studied for plant growth, Cu accumulation and nitrogen metabolism under Cu stress. At control, nitrate content in leaves and roots of metallicolous population (MP) showed little difference from those of non-metallicolous population (NMP). At 10 μM Cu treatment, nitrate content in leaves and roots of MP were significantly higher than those of NMP. Cu treatments significantly reduced nitrate reductase activity in leaves and roots of NMP compared with the controls while not in MP. Shoot and root biomass of NMP were inhibited more significantly than those of MP. Cu concentration in shoot and root of NMP were higher than those of MP both at control and under Cu stress. These results suggested less Cu absorbed and efficient nitrogen metabolism in MP might be partly reasons why R. dentatus can colonize Cu enriched soils.

Polyamines modulate nitrate reductase activity in wheat leaves: involvement of nitric oxide

In the present work, the effect of polyamines (PAs) on nitrate reductase (NR) activity was studied in wheat leaves exposed to exogenously added PAs while assessing the nitric oxide (NO) involvement in the regulation of the enzyme activity. A biphasic response was observed along the time of treatment using 0.1 mM of putrescine (Put), spermidine (Spd) or spermine (Spm). At 3 h, Spd and Spm significantly reduced NR activity by 29 or 35%, respectively, whereas at 6 h, the activity of the enzyme decreased by an average of 25%. At 21 h, Put increased NR activity by 63%, while Spd and Spm elevated the enzyme activity by 114%. NR activity, that was reduced by 0.1 mM Spm at 3 and 6 h, returned almost to control values when c-PTIO (an NO scavenger) was used, confirming that NO was involved in the inhibition of NR activity. Nitric oxide was also mediating the PA-increase of the enzyme activity at longer incubation times, evidenced when the raise in NR activity produced by 0.1 mM Spm at the longest incubation time returned to the value of the control in the presence of cPTIO. Neither the protein expression nor the nitrate content were modified by PAs treatments. The involvement of PAs and NO in the regulation of NR activity is discussed.

The Regulatory Region Controlling the Nitrate-Responsive Expression of a Nitrate Reductase Gene, NIA1, in Arabidopsis

Nitrate reductase (NR) is the enzyme that catalyzes the first step of nitrate assimilation. It is well known that the expression of NR genes is rapidly induced in various plants by nitrate. Previously, the activity of a tobacco NR gene promoter was reported to be high in tobacco plants grown on medium containing ammonium as the sole nitrogen source, but low in tobacco plants grown on nitrate-containing medium. This cast some doubt on the role of the NR gene promoter in the nitrate-inducible expression of this gene. Furthermore, in previous studies, transformation with genomic fragments containing NR loci restored the reduced NR activity in NR mutants to a limited extent, suggesting a complex regulation of NR gene expression. Here, we show that although the 1.9 kb promoter of an NR gene in Arabidopsis, NIA1, is not activated by nitrate, the expression of a GUS (β-glucuronidase) reporter gene inserted between the 5'- and 3'-flanking sequences of the NIA1 coding region is strongly induced by nitrate. When the 3'-flanking sequence was fused downstream of the GUS gene under the control of the 35S minimal promoter, its expression was also strongly induced by nitrate. Furthermore, dissection analysis of the 3'-flanking region revealed that the sequence downstream of the transcriptional terminator rather than the 3'-untranslated region plays a role in nitrate-inducible expression, indicating a requirement for the 3'-flanking sequence for the nitrate-inducible transcription of NIA1. We also show that the 2.7 kb promoter sequence of NIA2, another NR gene of Arabidopsis, cannot direct nitrate-inducible expression.

Effect of salt and water stresses on growth, nitrogen and phosphorus metabolism in Cucumis sativus L. seedlings

Plants exposed to osmotic stress exhibit changes in their physiology and metabolism. In general, osmotic stress reduces water availability and causes nutritional imbalance in plants. In the present study, we compared the response of cucumber (&lt;em&gt;Cucumis sativus&lt;/em&gt; L. var. Władko F-1) to ionic (100 mmol•dm-3 NaCl) and osmotic stress (10% PEG 6000). Both stress factors reduced significantly fresh and dry weight of 7-day-old cucumber seedlings. Under PEG treatment reduction of cucumber dry mass was lesser than in fresh mass, whereas under salt stress decrease in dry weight of cucumber shoots was more pronounced than in fresh mass. Salt stress caused severe decrease in nitrate concentration and activity of nitrate reductase (NR). In cotyledons nitrate content declined to 17% of the control and similar reduction in NR activity was observed. In the roots, observed changes were not so drastic but there was also strong interaction between reduction in nitrate content and NR activity. Under 10% PEG both nitrate concentration and NR activity in cucumber roots were significantly higher in comparison to control plants. In cotyledons NR activity was significantly lower than in control plants, while decrease in nitrate content was not statistically significant. Phosphate concentration did not change significantly in cucumber cotyledons but increased in roots treated both NaCl (32% increase) and PEG (53% increase). Similar tendencies were observed in acid phosphatase activity. Obtained results indicated that osmotic and salt stresses evoke differential responses, particularly in growth reduction and nitrogen metabolism in cucumber seedlings.

Nitric oxide inhibits nitrate reductase activity in wheat leaves

Nitrate reductase (NR), a committed enzyme in nitrate assimilation, is involved in the generation of nitric oxide (NO) in plants. In wheat leaf segments exposed to sodium nitroprusside (SNP) or S-nitrosoglutathione (GSNO), NR activity was significantly reduced to different degrees between 3 and 21h, whereas its activity was partially recovered when the NO scavenger cPTIO was used. At 21h, NR activity decreased from 38% with 10μM SNP to 91% with 500μM SNP, respect to the C values. S-nitrosoglutathione reduced NR activity between 18% and 26% only at 3h. When added directly to the incubation solution, NR activity was quickly and strongly inhibited more than 90% by 10 or 50μM SNP, whereas 10μM GSNO reduced the enzyme activity an average of 50%, at 30min of incubation. l-NAME and d-arginine (nitric oxide synthase (NOS) inhibitors) increased NR activity by 14% and 52% respectively, at 21h of exposure, leading us to suppose that endogenous NOS-dependent NO formation could also be modulating NR activity. NR protein expression was not affected by 10 or 100μM SNP at 3 or 21h of incubation, whereas nitration of tyrosines was not detected in the NR protein. Nitrates, which content increased along the time in the tissues, could be exerting a role in this regulation.

Salicylic Acid Protects Nitrate Reductase Activity, Growth and Proline in Amaranth and Tomato Plants during Water Deficit

Problem statement: Seedlings of Amaranthus hybridus cv. NHAC-3 (large green, amaranth) and Lycopersicum esculentum cv. Roma (tomato) were subjected to 7 days water stress at Early Vegetative (EV), Late Vegetative (LV), Early Flowering (EF) and Late Flowering (LF) stages of growth to study the impact on leaf water potential (ψw), Nitrate Reductase Activity (NRA), growth (plant height, shoot and root biomass) and proline content of both plants. Approach: Two concentrations of salicylic acid (1 and 3 mM SA) were applied to stressed plants to study the level of protection given by SA to the plants. Leaf ψw was significantly reduced (p = 0.05) during stress treatment at nearly all stages of growth in both plants. Leaf ψw was in the range -0.25 to -1.42 (unstressed) and -1.45 to -2.02 (stressed) in tomato plants while in amaranth it was -0.7 to -1.62 (unstressed) and -1.62 to -2.68 (stressed). As 3 mM SA increased leaf ψw to values close to the control (unstressed plants). NRA was significantly (p = 0.05) reduced by stress treatment at the LV stage of amaranth, EF stage of tomato and LF stage of both plants. Results: Thus, the reduction of NRA was more pronounced at the reproductive stage of both plants. As 3 mM SA was effective in maintaining NRA at levels similar to the control in both plants. Stress treatment reduced plant height significantly (p = 0.05) at the vegetative stages of both plants and 3 mM was also effective in keeping plant height similar to the control. Though shoot biomass was affected by water stress, SA treatment was not very effective in preserving the biomass during stress. Root biomass of plants was reduced by stress treatment at the reproductive stage and only tomato plants responded positively to 3 mM SA. Proline content was only slightly increased at all stages of growth in stressed plants but 3 mM SA induced a two-fold increase in proline content at the vegetative stage of tomato (EV and LV) and significant increases (p = 0.05) at almost all stages of growth of amaranth. Conclusion/Recommendations: The build up of proline, an osmolyte, by SA in stressed plants increased the capacity of plants to absorb water from the soil as shown by the increase in leaf ψw of both plants from -1.45 to -0.25 . SA was more effective in protecting the plants against the adverse effects of water stress when the stress was given at the vegetative stages (EV and LV) than at the flowering stages (EF and LF).

Nitrate uptake and metabolism by roots of soybean plants under oxygen deficiency.

Nitrate is reported to improve tolerance of plants towards oxygen deficiency enabled by waterlogging of the root system, but the mechanism underlying the phenomenon remains poorly understood. We studied the metabolism of nitrate in roots exposed to hypoxia, using soybean plants growing in a hydroponic system after suspending aeration and covering the surface of the nutrient solution with mineral oil. Nitrate depletion from the medium was more intense under hypoxia than normoxia, but in the presence of chloramphenicol, consumption under hypoxia was significantly reduced. Nitrite accumulated in the medium in the state of hypoxia and this effect was partially eliminated by chloramphenicol. Nitrate consumption sensitive to chloramphenicol was attributed to bacterial activity. Endogenous root nitrate was strongly reduced under hypoxia indicating mobilization. Although the transport of nitrate to the shoot via the xylem was also reduced under hypoxia, the severity of this reduction was dependent on the concentration of nitrate in the medium, suggesting that at least some of the nitrate in the xylem came from the medium. Root nitrate reductase was also strongly reduced under hypoxia, but recovered rapidly on return to normoxia. Overall, the data are consistent with two main metabolic fates for chloramphenicol-insensitive nitrate depletion under hypoxia: the reduction of some nitrate to nitrite (despite the reduced nitrate reductase activity) followed by its release to the medium (at least one-third of the nitrate consumed followed this route), and the transport of nitrate to the shoot. Nevertheless, it is highly unlikely that these metabolic routes account for all the nitrate consumed.