NaCl-stressed Rice Research Articles

Beneficial Effects of Hemin on Antioxidative Capacity and Anatomical Characters of NaCl-Stressed Rice Plants

Beneficial Effects of Hemin on Antioxidative Capacity and Anatomical Characters of NaCl-Stressed Rice Plants

Regulation of thermodynamics and kinetics of silica nucleation during the silicification process in higher plants

The formation mechanism of SiO2 aggregates is controversial because two contrasting hypotheses are often proposed to explain plant silicification. In this review, we summarize the physicochemical fundamentals of amorphous silica nucleation and discuss how plants regulate the process of silicification by influencing the thermodynamics and kinetics of silica nucleation. At silicification positions, plants overcome the thermodynamic barrier by establishing the supersaturation of the H4SiO4 solution and reducing the interfacial free energy. Among the thermodynamic-drivers, the establishment of supersaturation of H4SiO4 solution mainly depends on the expression of Si transporters for H4SiO4 supply, evapotranspiration for concentrating Si, and the other solutes in H4SiO4 solution for influencing the dissolution equilibrium of SiO2; while the interfacial free energy was reduced seemingly by the overexpression Na+/H+ antiporter SOS1 in high NaCl-stressed rice. Moreover, some kinetic-drivers, such as silicification-related proteins (Slp1 and PRP1) and new cell wall components, are actively expressed or synthesized by plants to interact with silicic acid, thereby reducing the kinetic barrier. According to classical nucleation theory, when the thermodynamic barrier is overcome, the super-saturated silicic acid solution (such as H4SiO4 in xylem sap) does not necessarily have to precipitate, just has the potential ability to precipitation. Thus, based on the mediators of SiO2 deposition at the thermodynamic-driven stage, it is difficult to evaluate whether the process of plant silicification is active or passive. We conclude that the characteristics of kinetic-drivers determine the mechanism of plant silicification.

Exogenous Calcium Supplementation Improves Salinity Tolerance in BRRI Dhan28; a Salt-Susceptible High-Yielding Oryza Sativa Cultivar

Salinity is one of the most brutal abiotic stressors, commencing a great stumbling block in the way of attaining food security in Bangladesh. Cultivation of rice in saline soils can be possible after enhancing its salt tolerance. This study aimed to examine the potential impact of exogenous calcium (3 and 5 mM Ca2+ in CaCl2) on conferring salt tolerance in rice (cv. BRRI dhan28). At the germination stage, Ca2+-primed seeds were grown under 100 mM NaCl stress conditions for nine days. At the seedling stage, rice seedlings were grown in a sandponic culture with Hoagland′s nutrient solution amended or not amended with 100 mM NaCl for 20 days with or without Ca2+ supplementation. Our results revealed that NaCl-stressed rice plants showed highly compromised germination indices and growth parameters, which could be attributed to reduced shoot and root growth, decreased photosynthetic pigments, increased H2O2 accumulation, and elevated levels of lipid peroxidation measured as malondialdehyde (MDA). On the other hand, exogenous Ca2+ application noticeably improved germination indices, growth and biomass-related parameters under salt stress. Ca2+-treated salt-stressed plants displayed amplified chlorophyll content, as well as suppressed the accumulation of H2O2, contributing to oxidative damage protection. Ca2+ supplementation for salt-stressed rice seedlings elevated relative water content without increasing excess proline, indicating the role of Ca2+ in maintaining water balance under stressful conditions. Furthermore, exogenous Ca2+ decreased membrane injury under NaCl stress, as mirrored by notably diminished levels of MDA in stressed seedlings. The defensive role of Ca2+ counter to oxidative stress was connected with the elevated activities of antioxidant enzymes such as catalase, ascorbate peroxidase, and peroxidase. In general, the best results in terms of growth at both germination and seedling stages were obtained in response to 3 mM Ca2+ treatment. Finally, Ca2+ supplementation can be an effective practice to cultivate rice in saline soils.

Mechanism of growth amelioration of NaCl-stressed rice (Oryza sativa L.) by .DELTA.-aminolevulinic acid

The mechanism of growth amelioration of NaCl-stressed rice (Oryza sativa L. cv. Nipponbare) by δ-aminolevulinic acid (ALA) was investigated. Rice growth recovered when plants were pretreated with 0.1 or 1 μM ALA before treatment with 50 mM NaCl. There was no increase in chlorophyll content by ALA treatment, indicating that the growth recovery was not due to increased chlorophyll content although ALA is a precursor of chlorophyll biosynthesis. The activities of antioxidative enzymes, including catalase (CAT), glutathione reductase (GR), ascorbate peroxidase (APx), and superoxide dismutase (SOD), increased with ALA treatment. In particular, stimulation of CAT, GR, and APx activities by ALA was significant. The hydrogen peroxide (H2O2) content decreased after ALA treatment under NaCl-stress conditions. Peroxidation of membrane lipids, as measured by ethane evolution, also decreased after ALA treatment. These results suggest that ALA induces growth amelioration in NaCl-stressed rice by stimulating antioxidative enzyme activity, which resulted in decreased reactive oxygen generation and lipid peroxidation.

Molecular regulation of starch accumulation in rice seedling leaves in response to salt stress

In this report we show that the starch content decreased in NaCl-stressed rice (Oryza sativa L.) seedling leaves during the daytime. Because photosynthetic efficiency and starch degradation enzyme activity were not significantly affected by the high salt, it is likely that this effect results from repression of starch biosynthesis. To determine the regulatory mechanism, the activities of enzymes such as ADP-glucose pyrophosphorylase (AGPase), granule-bound starch synthase (GBSS), soluble starch synthase (SSS) and starch branching enzyme (SBE) involved in starch synthetic pathway were examined. Data suggest that NaCl-induced repression of GBSS activity was the most significant factor reducing starch accumulation. Based on real-time RT-PCR analysis, the effect of salinity on GBSS expression was primarily controlled on the transcriptional level. Furthermore, the salt-induced decrease of both GBSSI and GBSSII gene expressions could be mostly contributed by ion-specific effect and not by osmotic stress. Although the mRNA accumulation of GBSSI and GBSSII can be down-regulated by exogenous ABA, the negative influence of salt stress on GBSSI and II gene expression could be chiefly mediated via an ABA-independent pathway.

Scavenging of reactive oxygen species in NaCl-stressed rice ( Oryza sativa L.)—differential response in salt-tolerant and sensitive varieties

Salinity stress affects the metabolism of plant cells leading to severe crop damage and loss of productivity. Oxidative stress is one consequence of salinity that may be responsible for much of the damage. We investigated the immediate responses (enzymatic and non-enzymatic) to salinity-induced oxidative stress in two major rice ( Oryza sativa L.) cultivars, salt sensitive Pusa Basmati 1 (PB) and salt-tolerant Pokkali (PK). Seedlings of both cultivars were subjected to NaCl stress (100–300 mM) for 42 h. Under NaCl stress, the salt-tolerant cv. PK showed higher activity of the ROS scavenging enzyme, catalase (CAT) and enhanced levels of antioxidants like ascorbate (ASC) and glutathione (GSH), than the sensitive cv. PB. Although superoxide dismutase (SOD) activity was lower in cv. PK, it showed lesser extent of membrane damage (lipid peroxidation) and lower levels of H 2O 2 than cv. PB under stress. The high levels of catalase activity indicate efficient scavenging of H 2O 2, which is produced more by non-enzymatic means than via SOD in cv. PK. These data indicate that concerted action of both enzymatic and non-enzymatic ROS scavenging machineries is vital to overcome salinity-induced oxidative stress in rice.

Cell wall peroxidase against ferulic acid, lignin, and NaCl-reduced root growth of rice seedlings

Summary The changes in cell wall peroxidase activity against ferulic acid (FPOD) and lignin level in roots of NaCl-stressed rice seedlings and their correlation with root growth were investigated. Increasing concentrations of NaCl from 50 to 150 mmol L −1 progressively decreases root growth. The reduction of root growth by NaCl is closely correlated with the increase in FPOD activity extracted from the cell wall. In contrast, lignin level was reduced by NaCl. Since proline and ammonium accumulations are associated with root growth inhibition caused by NaCl, we determined the effect of proline or NH 4 Cl on root growth and FPOD in roots. Exogenous application of NH 4 Cl or proline markedly inhibited root growth and increased FPOD activity in rice seedlings in the absence of NaCl. An increase in FPOD activity in roots preceded inhibition of root growth caused either by NaCl, NH 4 Cl, or proline. Our results suggest that cell-wall stiffening catalyzed by FPOD may participate in the regulation of root growth reduction of rice seedlings caused by NaCl.

Cell wall peroxidase activity, hydrogen peroxide level and NaCl-inhibited root growth of rice seedlings

The changes in cell-wall peroxidase (POD) activity and H2O2 level in roots of NaCl-stressed rice seedlings and their correlation with root growth were investigated. Increasing concentrations of NaCl from 50 to 150 mM progressively reduced root growth and increased ionically bound cell-wall POD activity. NaCl had no effect on covalently bound cell-wall POD activities. The reduction of root growth by NaCl is closely correlated with the increase in H2O2 level. Exogenous H2O2 was found to inhibit root growth of rice seedlings. Since ammonium and proline accumulation are associated with root growth inhibition caused by NaCl, we determined the effects of NH4Cl or proline on root growth, cell-wall POD activity and H2O2level in roots. External application of NH4Cl or proline markedly inhibited root growth, increased cell-wall POD activity and increased H2O2 level in roots of rice seedlings in the absence of NaCl. An increase in cell-wall POD activity and H2O2 level preceded inhibition of root growth caused by NaCl, NH4Cl or proline. NaCl or proline treatment also increased NADH-POD and diamine oxidase (DAO) activities in roots of rice seedlings, suggesting that NADH-POD and DAO contribute to the H2O2 generation in the cell wall of NaCl- or proline-treated roots. NH4Cl treatment increased NADH-POD activity but had no effect on DAO activity, suggesting that NADH-POD but not DAO is responsible for H2O2 generation in cell wall of NH4Cl-treated roots.

Effect of NaCl stress on H2O2 metabolism in rice leaves

The effect of NaCl stress on H2O2 metabolismin detached rice leaves was studied. NaCl (200 mM)treatment did not cause the accumulation ofH2O2 and resulted in no increase in lipidperoxidation and membrane leakage of leaf tissues. The activities of peroxidase, ascorbate peroxidase,superoxide dismutase, and glutathione reductase wereobserved to be greater in NaCl-stressed rice leavesthan in control leaves. However, glycolate oxidasewas lower in NaCl-treated rice leaves than in thecontrol leaves. There was no difference in catalaseactivity between NaCl and control treatments. Theseresults suggest that some antioxidant enzymes can beactivated in response to oxidative stress induced byNaCl.

NaCl induced changes in ionically bound peroxidase activity in roots of rice seedlings

The changes in ionically bound peroxidase activity in roots of NaCl-stressed rice seedlings and their correlation with root growth were investigated. Increasing concentrations of NaCl from 50 to 150 mM progressively decreases root growth. The reduction of root growth by NaCl is closely correlated with the increase in ionically bound peroxidase activity. Since proline and ammonium accumulations are associated with root growth inhibition caused by NaCl, we determined the effects of proline or NH4Cl on root growth and ionically bound peroxidase activity in roots. External application of proline or NH4Cl markedly inhibited root growth and increased ionically bound peroxidase activity in roots of rice seedlings in the absence of NaCl. An increase in ionically bound peroxidase activity in roots preceded inhibition of root growth caused by NaCl, NH4Cl or proline. Mannitol inhibited root growth, but decreased rather than increased ionically bound peroxidase activity at the concentration iso-osmotic with NaCl. The inhibition of root growth and the increase in ionically bound peroxidase activity in roots by NaClis reversible and is associated with ionic rather than osmotic component.

Effects of Osmoprotectants upon NaCl Stress in Rice.

Plants accumulate a number of osmoprotective substances in response to NaCl stress, one of them being proline (Pro). While characterizing some of the changes in solute accumulation in NaCl-stressed rice (Oryza sativa L.), we identified several other potential osmoprotectants. One such substance, trehalose, begins to accumulate in small amounts in roots after 3 d. We performed a series of experiments to compare the effects of Pro and trehalose on ion accumulation to determine whether the two chemicals protect the same physiological processes. We found that Pro either has no effect or, in some cases, exasperates the effect of NaCl on growth inhibition, chlorophyll loss, and induction of a highly sensitive marker for plant stress, the osmotically regulated salT gene. By contrast, low to moderate concentrations of trehalose reduce Na+ accumulation, salT expression, and growth inhibition. Somewhat higher concentrations (10 mM) prevent NaCl-induced loss of chlorophyll in blades, preserve root integrity, and enhance growth. The results of this study indicate that during osmotic stress trehalose or carbohydrates might be more important for rice than Pro.

Plant Regeneration and Screening From Long-Term NaCl-Stressed Rice Callus

Plant Regeneration and Screening From Long-Term NaCl-Stressed Rice Callus