Identification of salt-stress responsive genes in rice (Oryza sativa L.) by cDNA array

To identify salt stress-responsive genes, we constructed a cDNA library with the salt-tolerant rice cultivar, Lansheng. About 15000 plasmids were extracted and dotted on filters with Biomeck 2000 HDRT system or by hand. Thirty genes were identified to display altered expression levels responding to 150 mmol/L NaCl. Among them eighteen genes were up-regulated and the remainders down-regulated. Twenty-seven genes have their homologous genes in Gen-Bank Databases. The expression of twelve genes was studied by Northern analysis. Based on the functions, these genes can be classified into five categories, including photosynthesis-related gene, transport-related gene, metabolism-related gene, stress- or resistance-related gene and the others with various functions. The results showed that salt stress influenced many aspects of rice growth. Some of these genes may play important roles in plant salt tolerance.     

Potato Responds to Salt Stress by Increased Activity of Antioxidant Enzymes

To understand the response of potato to salt stress, antioxidant enzyme activities and ion content were analyzed for a sensitive and a tolerant cultivar. Nodal cuttings of the tolerant cultivar, Kennebec, and the sensitive cultivar, Concord, were exposed to media without or with 30, 60, 90 or 120 mmol/L NaCI for 4 weeks. On exposure to NaCI, the length and fresh and dry weight of both shoots and roots of Concord showed greater decrease than those of Kennebec. The decrease in shoot growth was more severe than that of the root for both cultivars. The K^＋ content of shoots and roots of both cultivars was reduced in a dose-dependent manner by exposure to NaCl; the Na^＋ content increased. Activities of ascorbate peroxidase, catalase and glutathione reductase were increased in NaCl-exposed shoots of Kennebec; the corresponding activities in NaCI-exposed shoots of Concord were decreased. Roots of both cultivars showed similar changes in the activities of these enzymes on exposure to NaCI. These studies established that enzyme activities in Concord shoots are inversely related to the NaCI concentration, whereas those in Kennebec do not show a dose dependency, which is also the case for the roots of both cultivars. Our findings suggest that an increase in activity of antioxidant enzymes, such as ascorbate peroxidase, catalase and glutathione reductase, can contribute to salt tolerance in Kennebec, a salt resistant cultivar of potato.     

Overexpression of Rice Sphingosine-1-Phoshpate Lyase Gene OsSPL1 in Transgenic Tobacco Reduces Salt and Oxidative Stress Tolerance

Sphingolipids, including sphingosine-1-phosphate (S1P), have been shown to function as signaling mediators to regulate diverse aspects of plant growth, development, and stress response. In this study, we performed functional analysis of a rice (Oryza sativa) S1P lyase gene OsSPL1 in transgenic tobacco plants and explored its possible involvement in abiotic stress response. Overexpression of OsSPL1 in transgenic tobacco resulted in enhanced sensitivity to exogenous abscisic acid (ABA), and decreased tolerance to salt and oxidative stress, when compared with the wild type. Furthermore, the expression levels of some selected stress-related genes in OsSPL1-overexpressing plants were reduced after application of salt or oxidative stress, indicating that the altered responsiveness of stress-related genes may be responsible for the reduced tolerance in OsSPL1-overexpressing tobacco plants under salt and oxidative stress. Our results suggest that rice OsSPL1 plays an important role in abiotic stress responses.     

The OsDHODH1 Gene is Involved in Salt and Drought Tolerance in Rice

In the present paper, we identified and cloned OsDHODH1 encoding a putative cytosolic dihydroorotate dehydrogenase （DHODH） in rice. Expression analysis indicated that OsDHODH1 is upregulated by salt, drought and exogenous abscisic acid （ABA）, but not by cold. By prokaryotic expression, we determined the enzymatic activity of OsDHODH1 and found that overproduction of OsDHODH1 significantly improved the tolerance of Escherichia coil cells to salt and osmotic stresses. Overexpression of the OsDHODH1 gene in rice increased the DHODH activity and enhanced plant tolerance to salt and drought stresses as compared with wild type and OsDHODHl-antisense transgenic plants. Our findings reveal, for the first time, that cytosolic dihydroorotate dehydrogenase is involved in plant stress response and that OsDHODH1 could be used in engineering crop plants with enhanced tolerance to salt and drought.     

The ionic effects of NaCl on physiology and gene expression in rice genotypes differing in salt tolerance

The effects of ionic stress on the physiology and gene expression of two rice genotypes (IR4630 and IR15324) that differ in salt tolerance, were investigated by evaluating changes in the biomass, Na⁺ and K⁺ concentrations and applying the cDNA-AFLP technique to highlight changes in gene expression. Over 8 days of salinisation, the effect of NaCl on the reduction of biomass (dry weight) was apparent from 24 h after salinisation (the first time point), indicating that the consequences of the build up of Na⁺ (and Cl^-) in the leaves of both lines was rapid. Furthermore, root growth of IR15324 was much more sensitive to salt than that of IR4630 (the reduction in root dry weight compared to non-salinised plants was three times greater in IR15324 than IR4630). The two rice lines also differed in their Na⁺ accumulation in saline conditions, a difference that was more marked in the shoots, particularly at the final harvest, than in the roots. Under salt stress, the K⁺ content (µmol/shoot) increased over four successive harvests (24, 48, 96, 192 h) in both lines, but was always greater in IR4630 than in IR15324: differences in Na⁺/K⁺ ratio appear to be an important determinant of salt tolerance in rice. To separate osmotic from ionic effects of salt, mannitol was applied as a non-ionic osmoticum at an osmotic potential estimated to be equivalent to 50 mM NaCl. Messenger RNA was sampled at 0.5, 6, 24, 48 and 192 hours after salinisation. Several products (AFLP-bands) were detected, which were upregulated in the response to ionic effects of salt in the tolerant line (IR4630) and not expressed in the sensitive line (IR15324). Bioinformatic analysis indicated three of these AFLP-bands have a high-degree of sequence similarity with the genes encoding a proline rich protein, senescence associated protein and heat-shock protein. The data are novel in that they differentially highlight changes induced by the ionic rather than osmotic effects of salt and in a tolerant rather than a sensitive genotype. The possible roles of the products of these genes are discussed.     

QTLs for Na<Superscript>+</Superscript> and K<Superscript>+</Superscript> uptake of the shoots and roots controlling rice salt tolerance

An F₂ and an equivalent F₃ population derived from a cross between a high salt-tolerance indica variety, Nona Bokra, and a susceptible elite japonica variety, Koshihikari, were produced. We performed QTL mapping for physiological traits related to rice salt-tolerance. Three QTLs for survival days of seedlings (SDSs) under salt stress were detected on chromosomes 1, 6 and 7, respectively, and explained 13.9% to 18.0% of the total phenotypic variance. Based on the correlations between SDSs and other physiological traits, it was considered that damage of leaves was attributed to accumulation of Na⁺ in the shoot by transport of Na⁺ from the root to the shoot in external high concentration. We found eight QTLs including three for three traits of the shoots, and five for four traits of the roots at five chromosomal regions, controlled complex physiological traits related to rice salt-tolerance under salt stress. Of these QTLs, the two major QTLs with the very large effect, qSNC-7 for shoot Na⁺ concentration and qSKC-1 for shoot K⁺ concentration, explained 48.5% and 40.1% of the total phenotypic variance, respectively. The QTLs detected between the shoots and the roots almost did not share the same map locations, suggesting that the genes controlling the transport of Na⁺ and K⁺ between the shoots and the roots may be different.     

核黄素参与水稻非生物胁迫响应的分析

为探究核黄素在水稻非生物胁迫响应中的作用,以粳稻Kitaake和籼稻T98B为试验材料,考察了核黄素对2种材料的盐、高温、渗透、碱和氧化胁迫响应的影响,重点测定了盐和高温胁迫下水稻体内核黄素合成基因的表达和相关生理指标。结果表明,(1)施加外源核黄素有效提高了2种水稻材料的盐和高温胁迫耐受性,降低了渗透胁迫耐受性,而其氧化和碱胁迫耐受性不受影响。(2)逆境胁迫均不同程度地促进了核黄素在2种水稻材料中的积累,尤其在盐和高温胁迫下促进效果最明显。(3)盐和高温胁迫均诱导了核黄素合成酶基因的表达,促进了核黄素的生物合成,改善了水稻的胁迫耐受性。研究表明,非生物逆境胁迫能促进核黄素在水稻体内的合成和积累,外源核黄素也能明显提高水稻对盐和高温胁迫的耐受性,但却降低了其对渗透胁迫的耐受性。