Effects of salt stress on ion balance and nitrogen metabolism of old and young leaves in rice (Oryza sativa L.)

Abstract

BackgroundIt is well known that salt stress has different effects on old and young tissues. However, it remains largely unexplored whether old and young tissues have different regulatory mechanism during adaptation of plants to salt stress. The aim of this study was to investigate whether salt stress has different effects on the ion balance and nitrogen metabolism in the old and young leaves of rice, and to compare functions of both organs in rice salt tolerance.ResultsRice protected young leaves from ion harm via the large accumulation of Na+ and Cl− in old leaves. The up-regulation of OsHKT1;1, OsHAK10 and OsHAK16 might contribute to accumulation of Na+ in old leaves under salt stress. In addition, lower expression of OsHKT1;5 and OsSOS1 in old leaves may decrease frequency of retrieving Na+ from old leaf cells. Under salt stress, old leaves showed higher concentration of NO3− content than young leaves. Up-regulation of OsNRT1;2, a gene coding nitrate transporter, might contribute to the accumulation of NO3− in the old leaves of salt stressed-rice. Salt stress clearly up-regulated the expression of OsGDH2 and OsGDH3 in old leaves, while strongly down-regulated expression of OsGS2 and OsFd-GOGAT in old leaves.ConclusionsThe down-regulation of OsGS2 and OsFd-GOGAT in old leaves might be a harmful response to excesses of Na+ and Cl−. Under salt stress, rice might accumulate Na+ and Cl− to toxic levels in old leaves. This might influence photorespiration process, reduce NH4+ production from photorespiration, and immediately down-regulate the expression of OsGS2 and OsFd-GOGAT in old leaves of salt stressed rice. Excesses of Na+ and Cl− also might change the pathway of NH4+ assimilation in old leaves of salt stressed rice plants, weaken GOGAT/GS pathway and elevate GDH pathway.

Comparative physiological analysis of salinity tolerance in rice

“…Although, in our study, expression analysis was conducted only in leaves due to difficulties in harvesting root samples, repressed expression of the OsHKT1;5 gene in Juma67 may cause elevated Na + accumulation in the leaves under high salinity conditions. It was reported that down-regulation of the OsHKT1;5 expression may contribute to stimulation of Na + accumulation in old leaves (Wang et al 2012). Taken together with the evidence of the localization of the OsHKT1;5 transcript in aerial parts of rice (Ren et al 2005), repression of the OsHKT1;5 expression may reduce the function of Na + exclusion from shoots.…”

Novel Approach for High-Throughput Metabolic Screening of Whole Plants by Stable Isotopes

“…Stressed plants kept relatively more nitrogen in the root as compared with nonstressed plants (Fig. 3), probably to support the supply with nitrogen-containing compatible solutes (Wang et al, 2012). Furthermore, enhanced retention of nitrogen compounds in the root might be due to adaptive mechanisms to ensure adequate water and nutrient acquisition from the rhizosphere (Sharp et al, 2004).…”

Improvement of Salinity Stress Tolerance in Rice: Challenges and Opportunities

“…Several studies have suggested that a low cytosolic Na + /K + ratio is required to maintain a favourable ionic homeostasis in plant cells under salinity stress condition [41,42] and that a low Na + /K + ratio improves photosynthesis and overall plant growth [43]. Wang et al [44] reported that under salinity stress, genes related to sodium transport from roots to shoot such as OsHKT1;1, OsHAK10 and OsHAK16 were upregulated in the old leaves of rice. Meanwhile genes involved in facilitating Na + exclusion from root xylem vessels to reduce shoot accumulation, like OsHKT1;5 and OsSOS1, were downregulated, leading to high concentrations of Na + accumulated in old leaves compared to young leaves.…”