Study On The Improvement In Soda Saline-alkaline Tolerance Of Rice(Oryza Sativa L.) By S-ABA

There could be multiple ways to improve the rice tolerance to saline-alkaline stress(SA). In addition to screening for rice genetic resourses and employing elite cultivars with high SA-tolerance, exogenous application of stress-alleviating substance are also considered highly effective. The phytohormone abscisic acid(ABA) is known to play a vital role in the adaptive response of plants to various stresses including drought, salt and cold. ABA has two optical isomers, S-ABA and R-ABA, with S-ABA being the natural active form in plants. It can be produced by either chemical synthesis or fungal fermentation. However, previous studies have mainly focused on the physiological functions of ABA that is prouced by chemical synthesis(mixture of S-ABA and R-ABA), and only limited studies have been reported on regulatory roles of S-ABA in salt tolerance in rice. In this study, we conducted in-lab and field experiments to investigate whether the microbe-produced S-ABA can be used to improve the tolerance of rice seedlings to SA.The study contained following 3 experiments.(1) A collection of 60 representative local japonica rice cultivars from Jilin province, China, was evaluated for their SA-tolerance at the seed germination stage. The SA factors were simulated by 120 mM NaCl and 30 mM Na2CO3 solutions respectively. Five indices of seed germination were measured under stressed or unstressed control conditions.(2) Seedlings were pretreated with S-ABA at concentrations of 0, 5, 10, and 20 μM by root-drench for 24 h and then transferred to a NaCl or Na2CO3 solution in the laboratory experiment.(3) Field experiments were conducted, based on results of in-lab experiments, to further assess the effect of S-ABA on stress tolerance of rice plants in SA paddy fields. Rice seedlings were pretreated with S-ABA at concentrations of 0, 5, 10 and 20 μM by root-drench for 24 h just before transplanting to two differently SA-leveled paddy fields.The expermental results of the study revealed following 3 main topics:(1) Based on the membership degree, we identified varieties with different tolerance level to SA facotors. We chose Dongdao 4 as tolerant to both the saline and alkaline; Jiudao 51 as sensitive to both the saline and alkaline stresses. Both of them were used into the laboratory experiment of rice seedlings.(2) In the laboratory experiment, S-ABA at low concentration(1 μM,5 μM) showed the most siginificant effect in alleviating SA-damages on rice seedling growth. By contrast, high concentration(20 μM) of S-ABA inhibited to some extent the growth of rice seedlings. After 6 days under the stress conditions, pretreatment with ABA substantially improved the fresh weight(FW) and the relative water content(RWC) of shoot, increased the survival rate, total chlorophyll, shoot K+ of rice seedlings, and significantly reduced the shoot Na+, root Na+ and Na+/K+ of rice seedlings compared to control treatment. The tolerance of Dongdao 4 to saline-alkaline stress was better than Jiudao 51 due probably to morphological characteristics and saline-alkaline sensitivity of root.(3) In the field experiment, pretreatment with S-ABA substantially reduced the occurrence of leaf withering, enhanced rooting ability and tiller number compared to control treatment. Meanwhile,expressions of ABA-responsive genes SalT and OsWsi18 were highly induced by S-ABA treatment. Further, S-ABA application also significantly enhanced the final grain yield; the most significant effect was seen at 10 μM, with 27.9% increase in grain yield in high SA-leveled paddy fields.