关键词: 粳稻, 盐胁迫, 叶绿素荧光参数, 诱导动力学曲线, 实时荧光定量PCR

Abstract:

【Objective】Chlorophyll fluorescence parameters can reflect the damage degrees and stress resistance of the plant photosynthetic machinery under salt stress. In this study, the analysis of effects of salt stress on chlorophyll fluorescence characteristics of japonica rice with different salt tolerances was performed to reveal its induced kinetic characteristics and preliminarily elucidate the mechanism of OsHCF222 and OsABCI7 regulating salt tolerance of japonica rice at seedling stage, so as to provide a theoretical foundation for screening and breeding salt-tolerant rice varieties.【Method】Eight salt-tolerant and eight salt-sensitive japonica rice germplasm accessions were used as experimental materials in this study. Leaf chlorophyll fluorescence parameters were measured for these materials after treatment using 0 mmol·L^-1 or 125 mmol·L^-1 NaCl for 3 or 6 days. Principal component analysis (PCA) was used to screen the key indexes for salt tolerance, and a comprehensive evaluation of japonica rice germplasm was carried out with membership functions and weighted standard deviation coefficient method. The resulting salt-tolerant and salt-sensitive germplasm were used to analyze the relative expressions of OsHCF222 and OsABCI7, two chlorophyll fluorescence related genes. 【Result】Compared with the control (CK, 0 mmol·L^-1 NaCl for 3 days or 6 days), the salt stress treatment (125 mmol·L^-1 NaCl 3 days or 6 days) significantly reduced the maximal fluorescence (F_m) and maximum quantum efficiency of PSII (F_v/F_m) of japonica rice germplasm. For salt tolerant germplasm accessions, the non-photochemical quenching coefficient (NPQ) and coefficient of non-photochemical quenching of variable fluorescence (qN) decreased significantly at 3 days after salt stress, while the initial fluorescence yield (F_o) increased significantly at 6 days after salt stress. The photochemical quenching coefficient (qP) and qN of the salt-sensitive germplasm accessions decreased significantly on the 3rd day after salt stress treatment, while the indexes including yield (Y), NPQ and photosynthetic electron transfer rate (ETR) decreased significantly on the 3rd and 6th day after salt stress treatment. Under salt stress, F_m, F_v/F_m, Y, NPQ and ETR were positively correlated with salt tolerance score (STS), and there were significant differences between salt-tolerant and salt-sensitive japonica rice germplasm accessions. PCA with eight chlorophyll fluorescence parameters revealed two major components, with a cumulative contribution rate of 88.018%. Five key indexes, including F_m, F_v/F_m, Y, NPQ and ETR, were selected based on the loading of each component. The 16 accessions were subsequently assigned to salt tolerant and salt sensitive groups by cluster analysis. A comprehensive evaluation value D (D_CF) of chlorophyll fluorescence characteristics under salt stress was obtained by using membership function combined with the index weight method, and then the ranking of the 16 accessions was obtained. Chlorophyll fluorescence induction curves of salt-tolerant Cigalon and Bertone, salt-sensitive Xinzhu8 and Sachiminori under salt stress and CK were created using the Kinetic model. Under CK condition, the four japonica rice germplasm accessions showed similar curve shapes with a large slope and the occurrence time of P peak was basically the same. Under the salt stress treatment, peak P, peak M and the curve slope of salt-sensitive accessions decreased rapidly, while the salt-tolerant accessions still maintained high P peak and curve slope. Through quantitative real-time PCR analysis of OsHCF222 and OsABCI7 in Cigalon and Sachiminori at different times under NaCl stress, the dynamic changes and correlation between leaf chlorophyll content and five key chlorophyll fluorescence parameters, the potential role of the two genes in salt tolerance of japonica rice were preliminarily clarified. 【Conclusion】Chlorophyll fluorescence parameters of japonica rice germplasm with different salt tolerances responded differently to salt stress. F_m, F_v/F_m, Y, NPQ and ETR were closely related to salt tolerance in rice. The expression levels of OsHCF222 and OsABCI7 directly affected the salt tolerance of japonica rice germplasm at seedling stage. In salt-tolerant japonica rice, NPQ and F_v/F_m played as key indexes, while F_m might play an important role in salt-sensitive japonica rice.

Key words: Oryza sativa japonica, salt stress, chlorophyll fluorescence parameters, chlorophyll fluorescence induction curves, quantitative real-time PCR