Peroxidase activities of two rice cultivars differing in salinity tolerance as affected by proline and NaCl

Proline content, ion accumulation, cell wall and soluble peroxidase activities were determined in control and salt-treated calli (150 nM NaCl) and whole plants (30 mM NaCl) of two rice cultivars (salt sensitive cv. IKP and salt tolerant cv. Aiwu). Under salinity, the highest accumulation of Na⁺, Cl^? and proline occurred in calli, roots and younger leaves of cv. IKP, coupled with the highest decrease in K⁺ content; accumulations of Na⁺ and Cl^? were restricted to older leaves in cv. Aiwu. Relative growth rates of calli and roots or shoots from both cultivars were not linked to peroxidase activities. High concentrations (1 M) of exogenously applied glycerol did not inhibitin vitro activities of soluble peroxidase extracted from control and salt-treated calli or plants. Conversely, 35–55% (in cv. IKP) or 60–80% (in cv. Aiwu) of soluble peroxidase activities were found in presence of isosmotic proline concentration. There were no differences between proline and glycerol effects onin vitro cell wall peroxidase activities.     

Effects of exogenous proline and glycinebetaine on the salt tolerance of rice cultivars

Salinity significantly increased trisodium-8-hydroxy-1,3,6-pyrenetrisulphonic acid (PTS) uptake and decreased the K(+)/Na(+) ratio in salt-sensitive rice (Nipponbare) but did not markedly in salt-tolerant rice (Pokkali). Proline and glycinebetaine (betaine) suppressed the increase in PTS uptake and the decrease in the K(+)/Na(+) ratio in Nipponbare, but did not affect PTS uptake or the K(+)/Na(+) ratio in Pokkali.     

Physiological basis of differential response to salinity in rice cultivars

Growth analyses of rice Oryza sativa L. seedlings in salinized nutrient solution condition were conducted with 24 cultivars and lines after genetic purification. Cultivar differences in relative growth rate in salinized conditions were chiefly dependent on differences in shoot Na content. The shoot Na content was affected by Na selectivity in the root and by the leaf area ratio (LAR, leaf area per total dry weight). The contribution of LAR was equally important to that of root cultivar selectivity against Na uptake under a higher salinization condition where root selectivity against Na may be decreased due to reduced root activity. Cultivar differences in salt tolerance in highly salinized conditions were mainly attributed to differences in these two factors. A more convenient and efficient screening method for salt tolerance is proposed.     

Ozone effects on carbon metabolism in sensitive and insensitive Phaseolus cultivars

An ozone treatment of 165 nL L^?1 for 3 h evoked differential responses in the primary leaves of two bean cultivars of the common bean (Phaseolus vulgaris L.). While cv ‘Cannellino’ showed visible symptoms of injury within 24 h of exposure, no visible symptoms at all were evident in the cv ‘Top Crop’. In primary leaves of the sensitive cultivar Cannellino, we observed an increase in carbon breakdown (an increase in PFK and Fumarase) and a reduction in CO₂ photoassimilation, linked also to the diminished synthesis of sucrose (a decrease in SPS activity) and to the stimulation of the degradation of this sugar (an increase in SuSy and Invertase activities). A strong stimulation of PEPcase activity indicates both an increased synthesis of OAA and an enhanced replenishment of the tricarboxylic acid cycle. Finally, in Cannellino leaves the activity of NADP-malic enzyme increased indicating a stimulation of enzymes delivering NADPH. The findings of this research suggest that the visible symptoms in Cannellino represent an active response that this cultivar initiates to cope with excess oxidative load. The pattern in Top Crop was different. This cultivar did not show visible symptoms of injury, nor any responsive changes at the physiological and biochemical levels. Oxidative pathways are partially enhanced, e.g., increases in Invertase, PFK and IDH. There were also increases in some enzyme linked to the production of cytosolic NADPH as G6PD, probably caused by the slight increase in activity of the enzymes SKDH and PAL involved in synthesis of phenolic compounds. However, the absence of visible injury in Top Crop leaves is confirmation that, in this cultivar, the need to produce carbon skeleton and NADPH used in detoxification and repair process is lower.     

Phenolic compounds in date palm cultivars sensitive and resistant toFusarium oxysporum

In date palm (Phoenix dactylifera L.) leaves, the main compounds of the phenolic pool were quercetin and isorhamnetin heterosides, (+)-catechin and (-)-epicatechin. Although previously observed only in date palm fruits, 5-caffeoylshikimic acid (dactylifric acid) and its positional isomers (3-caffeoylshikimic acid and 4-caffeoylshikimic acid) were detected also in the leaves and roots. Quantitative, but not qualitative, differences between cultivars resistant and susceptible toFusarium oxysporum f. sp.albedinis during growth period were observed Acknowledgements: The authors are very grateful to Dr. Janati, Director of SCAS (INRA, Marrakech) for supplying the plant material used in this study. The study was funded by the Programme de Cooperation Franco-Marocaine (Al 473/90) between Cadi Ayyad University (Marrakech, Maroc) and Montpellier II University (France)     

Effect of the proline analogue baikiain on proline metabolism in Salmonella typhimurium

A proline analogue, 4,5-dehydro-l-pipecolic acid (baikiain) induces the formation in Salmonella typhimurium of the two enzymes catalyzing the degradation of proline, proline oxidase and Delta(1)-pyrroline-5-carboxylic acid (P5C) dehydrogenase. The level of induction by 20 mm baikiain is about 10% of the maximum level induced by proline. Since the analogue is a substrate of proline oxidase the first enzyme of the proline catabolic pathway, the oxidation derivative rather than baikiain itself might be the actual effector. Baikiain is also an inducer of proline oxidase in Escherichia coli K-12 and E. coli W. An additional effect of this analogue on proline degradation in S. typhimurium is inhibition of P5C dehydrogenase. At a concentration of 5 x 10(-4)m, baikiain inhibits completely the growth of strains constitutive for proline oxidase. This inhibition, which can be overcome by proline, occurs in the presence or absence of P5C dehydrogenase activity. Three spontaneously occurring mutants resistant to baikiain were isolated from constitutive strains. All are pleiotropic-negative for the proline-degrading enzymes. The sites of these mutations are linked to the put region. Although the mechanism of toxicity has not been determined, baikiain provides a simple and direct selection for obtaining mutants unable to degrade proline. In addition, it allows selection for strains with an inducible rather than constitutive phenotype.     

Effect of salinity on chlorophyll and proline contents in three aquatic macrophytes

The role of proline in imparting tolerance to salinity was investigated in Hydrilla verticillata, Najas indica and Najas gramenia. The plants were exposed to different concentrations of NaCl and artificial sea water (SWS) separately. The chlorophyll (Chl) a/b ratio decreased significantly in all the three plant species in both NaCl and SWS treatments, comparatively more in former than the latter. NaCl resulted in drastic decrease in this ratio in salt sensitive H. verticillata and N. indica, but in somewhat lesser decrease in salt resistant N. gramenia. Proline content increased at both NaCl and SWS treatments, especially at the latter. However, in H. verticillata proline content at 1.5 and 2.5 % NaCl decreased. It was concluded that proline cannot be used as a biochemical marker of salt tolerance in aquatic plants, however, the decrease in Chl a/b ratio in response to NaCl may be used as an index of salt sensitivity in this ecological group of plants. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of drought on enzymes and free proline in rice varieties

Drought tolerant rice variety TKM-1 and susceptible variety Improved Sabarmati (I.S.) showed characteristic differences in peroxidase, RNase, nitrate r     

NaCl effects on proline metabolism in rice (Oryza sativa) seedlings

Salt-stress effects on osmotic adjustment, ion and proline concentrations as well as proline metabolizing enzyme activities were studied in two rice ( Oryza sativa L.) cultivars differing in salinity resistance: I Kong Pao (IKP; salt-sensitive) and Nona Bokra (salt-resistant). The salt-sensitive cultivar exposed to 50 and 100 m M NaCl in nutritive solution for 3 and 10 days accumulated higher levels of sodium and proline than the salt-resistant cultivar and displayed lower levels of osmotic adjustment. Proline accumulation was not related to proteolysis and could not be explained by stress-induced modifications in Δ¹-pyrroline-5-carboxylate reductase (P5CR; EC 1.5.1.2) or proline dehydrogenase (PDH; EC 1.5.1.2) activities recorded in vitro. The extracted ornithine Δ -aminotransferase (OAT; EC 2.6.1.13) activity was increased by salt stress in the salt-sensitive cultivar only. In both genotypes, salt stress induced an increase in the aminating activity of root glutamate dehydrogenase (GDH; EC 1.4.1.2) while deaminating activity was reduced in the leaves of the salt-sensitive cultivar. The total extracted glutamine synthetase activity (GS; EC 6.3.1.2) was reduced in response to salinity but NaCl had contrasting effects on GS1 and GS2 isoforms in salt-sensitive IKP. Salinity increased the activity of ferredoxin-dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) extracted from leaves of both genotypes and increased the activity of NADH-dependent glutamate synthase (NADH-GOGAT; EC 1.4.1.14) in the salt-sensitive cultivar. It is suggested that proline accumulation is a symptom of salt-stress injury in rice and that its accumulation in salt-sensitive plants results from an increase in OAT activity and an increase in the endogenous pool of its precursor glutamate. The physiological significance of the recorded changes are analyzed in relation to the functions of these enzymes in plant metabolism.     

Effects of NaCl stress on germination, antioxidant responses, and proline content in two rice cultivars

We investigated the physiological and biochemical bases for salt tolerance in two rice (Oryza sativa L.) cultivars — relatively salt-tolerant ‘Dongjin’ and salt-sensitive ‘Kumnam’. Salinized hydroponic cultures were studied at the germination and seedling stages. NaCI inhibited germination more severely in ‘Kumnam’ than in ‘Dongjin’. Increasing the salt concentration also deterred growth to a larger extent in the former. Moreover, the leaves of ‘Kumnam’ exhibited greater increases in lipid peroxidation and Na⁺ accumulation than those of ‘Dongjin’ under stress. The activities of constitutive and salt-induced superoxide dismutase (SOD, EC 1.15.1.1) and ascorbate peroxidase (AP, EC 1.11.1.11) were also higher in ‘Kumnam’, while only catalase (CAT, EC 1.11.1.6) activity was slightly higher in stressed plants of ‘Dongjin’. The positive correlation between leaf proline levels and NaCI concentration was more evident in ‘Kumnam’. However, ‘Dongjin’ seeds, which had higher germinability in the presence of NaCI, also contained more proline. These results suggest that the higher salt tolerance in ‘Dongjin’ seedlings could be ascribed to their lower NaCI accumulations in the leaves. This presumably is due to reductions in the uptake or transport rates of saline ions to the shoots from the roots. Finally, we believe that the higher germination rate by ‘Dongjin’ is caused by its higher seed proline content.     

Free proline contents in two different groups of rice mutants resistant to hydroxy-L-proline

Summary In four rice (Oryza sativa L.) mutants resistant to hydroxy-L-proline (Hyp), HYP101, HYP203, HYP205 and HYP210, and in their original variety, Nipponbare, free proline and Hyp contents in the seeds and in the 14-day-old seedlings have been determined. The four mutants can be divided into two groups: HYP101 and HYP203 are classified as to recessive gene and the levels of free proline are similar to that of the original variety; the second group includes mutants HYP205 and HYP210 where the Hyp resistance is transmitted heterozygously and, both in the seeds and in the seedlings, a remarkable increase in free proline content is observed. In particular, free proline contents in the seeds of HYP205 and HYP210 are, respectively, 24 and 12 times that of the original variety. Hyp is detected only in the seedlings cultured with Hyp solution. In the Hyp resistant seedlings of HYP205 and HYP210, Hyp contents are twice that of the original variety and less than half in the seedlings of HYP101 and HYP203. Hyp resistance and differential proline levels are also evident in the callus initiated from the mutants. This suggests that the Hyp resistant mutants are good genetic markers both in planta and in vitro. The Hyp mutants are also discussed with regard to stress resistance.     

Effects of salt stress on growth, mineral nutrition and proline accumulation in relation to osmotic adjustment in rice (Oryza sativa L.) cultivars differing in salinity resistance

Salt-resistant rice cultivars Nona Bokra and IR 4630 exposed at the seedling stage during one or two weeks to 0, 20, 30, 40 or 50 mM NaCl accumulated less Na, Cl, Zn and proline and more K at root and shoot levels than salt-sensitive I Kong Pao and IR 31785. Aiwu, a moderately resistant genotype, exhibited an intermediate behaviour. P transport from root to shoot was inhibited in the most sensitive cultivar IR 31785. Accumulation of Na and Cl and decrease in K content at the shoot level were restricted to the oldest leaves in salt-resistant genotypes while proline accumulated in the youngest leaves in all cultivars. In the presence of NaCl, the osmotic potentials of the roots and of the oldest and youngest leaves were lower in the salt-resistant than in the salt-sensitive genotypes, differences among genotypes increasing with stress intensity. Proline did not appear to be involved in osmotic adjustment in salt-stressed rice plants and the significance of its accumulation is discussed in relation to salinity resistance.Abbreviations cv(s). cultivar(s) - EC electrical conductivity - IKP I Kong Pao - J rate of ion transport - MCW methanol-chloroform-water - PAR photon flux density - Pc partitioning coefficient - RGR mean relative growth rate - RI resistance index - s osmotic potential     

Salinity-induced changes in two cultivars of Vigna radiata: responses of antioxidative and proline metabolism

The influence of increasing salinity stress on plant growth, antioxidant enzymes and proline metabolism in two cultivars of Vigna radiata L. (cv. Pusa Bold and cv. CO 4) was investigated. Salt stress was imposed on 30-days-old cultivars with four different concentrations of NaCl (0, 100, 200 and 300 mM). The roots and shoots of CO 4 showed greater reduction in fresh weight, dry weight and water content when compared to Pusa Bold with increasing salt stress. Under salinity stress, the roots and shoots of CO 4 exhibited higher Na⁺: K⁺ ratio than Pusa Bold. The activities of reactive oxygen species (ROS) scavenging enzymes and reduced glutathione (GSH) concentration were found to be higher in the leaves of Pusa Bold than in CO 4, whereas oxidized glutathione (GSSG) concentration was found to be higher in the leaves of CO 4 compared to those in Pusa Bold. Our studies on oxidative damage in two Vigna cultivars showed lower levels of lipid peroxidation and H₂O₂ concentration in Pusa Bold than in CO 4 under salt stress conditions. High accumulation of proline and glycine betaine under salt stress was also observed in Pusa Bold when compared to CO 4. The activities of proline biosynthetic enzymes were significantly high in Pusa Bold. However, under salinity stress, Pusa Bold showed a greater decline in proline dehydrogenase (ProDH) activity compared to CO 4. Our data in this investigation demonstrate that oxidative stress plays a major role in salt-stressed Vigna cultivars and Pusa Bold has efficient antioxidative characteristics which could provide better protection against oxidative damage in leaves under salt-stressed conditions.     

Bisulphite sequencing reveals dynamic DNA methylation under desiccation and salinity stresses in rice cultivars

DNA methylation governs gene regulation in plants in response to environmental conditions. Here, we analyzed role of DNA methylation under desiccation and salinity stresses in three (IR64, stress-sensitive; Nagina 22, drought-tolerant and Pokkali, salinity-tolerant) rice cultivars via bisulphite sequencing. Methylation in CG context within gene body and methylation in CHH context in distal promoter regions were positively correlated with gene expression. Hypomethylation in Nagina 22 and hypermethylation in Pokkali in response to desiccation and salinity stresses, respectively, were correlated with higher expression of few abiotic stress response related genes. Most of the differentially methylated and differentially expressed genes (DMR-DEGs) were cultivar-specific, suggesting an important role of DNA methylation in abiotic stress responses in rice in cultivar-specific manner. DMR-DEGs harboring differentially methylated cytosines due to DNA polymorphisms between the sensitive and tolerant cultivars in their promoter regions and/or coding regions were identified, suggesting the role of epialleles in abiotic stress responses.     

Effect of low temperature on chloroplast structure in cultivars of rice

The chloroplasts in cold-susceptive indica varieties and indica? japonica lines swelled and then accumulated excess starchunder low temperature. Disorganization of the thylakoids anddiscoloration of the leaf were also observed. ¹ Home address: Kongju Teacher's College, Choong-Chung Nam Province,301 Korea. (Received April 7, 1979; )     

Water stress-induced alterations in the proline metabolism of drought-susceptible and -tolerant cassava (Manihot esculenta) cultivars

The free proline levels and activities of ornithine aminotransferase (EC 2.6.1.13) and proline oxidase (EC 1.5.2.2), two of the enzymes involved in proline metabolism were studied during the induction of water stress in a drought susceptible (M-4) and a drought tolerant (S-1315) cultivar of cassava ( Manihot esculenta Crantz). Water stress induced by polyethylene glycol (MW 6000, osmotic potential — 1.65 MPa) caused a ca 25-fold increase in proline in young excised leaves of the susceptible cultivar (M-4) while the increase was about 9-fold in the tolerant cultivar (S-1315). The activity of ornithine aminotransferase (OAT), a key enzyme involved in the biosynthesis of proline, was found to increase 3-fold in water stressed leaves of M-4 and about 2-fold in those of S-1315. The activity of proline oxidase, which is involved in the degradation of proline to pyrroline-5-carboxylate, was reduced by 50% in M-4 and nearly 25% in S-1315 on water stress. Comparison of the kinetic properties of OAT showed that the enzyme from water-stressed leaves is more stable to heat inactivation compared to that of control. These results indicate that during water stress there are alterations in the metabolism of proline in cassava, and the extent of alteration varies between drought-susceptible and -tolerant cultivars.     

Effect of respiratory homeostasis on plant growth in cultivars of wheat and rice

Some plants have the ability to maintain similar respiratory rates (measured at the growth temperature), even when grown at different temperatures, a phenomenon referred to as respiratory homeostasis. The underlying mechanisms and ecological importance of this respiratory homeostasis are not understood. In order to understand this, root respiration and plant growth were investigated in two wheat cultivars (Triticum aestivum L. cv. Stiletto and cv. Patterson) with a high degree of homeostasis, and in one wheat cultivar (T. aestivum L. cv. Brookton) and one rice cultivar (Oryza sativa L. cv. Amaroo) with a low degree of homeostasis. The degree of homeostasis (H) is defined as a quantitative value, which occurs between 0 (no acclimation) and 1 (full acclimation). These plants were grown hydroponically at constant 15 or 25 °C. A good correlation was observed between the rate of root respiration and the relative growth rates (RGR) of whole plant, shoot or root. The plants with high H showed a tendency to maintain their RGR, irrespective of growth temperature, whereas the plants with low H grown at 15 °C showed lower RGR than those grown at 25 °C. Among several parameters of growth analysis, variation in net assimilation rate per shoot mass (NAR_m) appeared to be responsible for the variation in RGR and rates of root respiration in the four cultivars. The plants with high H maintained their NAR_m at low growth temperature, but the plants with low H grown at 15 °C showed lower NAR_m than those grown at 25 °C. It is concluded that respiratory homeostasis in roots would help to maintain growth rate at low temperature due to a smaller decrease in net carbon gain at low temperature. Alternatively, growth rate per se may control the demand of respiratory ATP, root respiration rates and sink demands of photosynthesis. The contribution of nitrogen uptake to total respiratory costs was also estimated, and the effects of a nitrogen leak out of the roots and the efficiency of respiration on those costs are discussed.