Abstract
Using photothermosensitive genic male sterile (PTSGMS) rice (Oryza sativa L.) lines to produce hybrids can obtain great heterosis. However, PTSGMS rice lines exhibit low stigma vitality when high-temperature (HT) stress happens during anthesis. Jasmonates (JAs) are novel phytohormones and play vital roles in mediating biotic and abiotic stresses. Little is known, however, if and how JAs could alleviate the harm of HT stress during anthesis to the stigma vitality of PTSGMS lines. This study investigated the question. Two PTSGMS lines and one restorer line of rice were pot-grown and subjected to normal temperature and HT stress during anthesis. The stigma exertion rate, sigma fresh weight, stigma area, contents of JAs, hydrogen peroxide (H2O2), and ascorbic acid (AsA), activity of catalase in stigmas, and the number of pollens germinated on the stigma of PTSGMS lines were determined. The results showed that a rice line with higher JAs content in the stigma under HT stress showed lower H2O2 content, higher AsA content and catalase activity in stigmas, larger stigma area, heavier stigma fresh weight, more pollens germinated on the stigma, and higher fertilization and seed-setting and rates. Applying methyl JAs during anthesis to rice panicles decreased the accumulation of reactive oxygen species and enhanced stigma vitality, thereby increasing fertilization and seed-setting rates of the hybrids of PTSGMS rice lines under HT stress. The results demonstrate that JAs attenuate the injury of HT stress to the stigma vitality of PTSGMS rice lines through enhancing antioxidant ability.
Highlights
Using “two-line method” to produce hybrid rice (Oryza sativa L.), namely, a hybrid produced by a photothermosensitive genic male sterile (PTSGMS) line crossed with a restorer line, could produce great heterosis (Yang et al, 2003; Deng et al, 2013; Ma and Yuan, 2015; Yuan, 2017)
The results showed that a PTSGMS line with higher contents of jasmonic acid (JA) and methyl jasmonate (MeJA) in the stigmas under high temperature (HT) stress had better traits reflecting stigma vitality, such as heavier fresh weight of stigmas, larger stigma area, greater exertion rate of stigmas and more pollen number geminated on the stigma (Figures 1, 2; Supplementary Figure 2; Table 1), leading to higher fertilization percentage, seed-setting percentage, and seed yield when the line was crossed with a restorer rice line (Table 2)
A PTSGMS line with higher JA and MeJA contents in stigmas under HT stress had better traits reflecting stigma vitality including higher ascorbic acid (AsA) content and catalase activity and lower H2O2 content in the stigmas, heavier fresh weight of stigmas, larger single stigma area, greater exertion rate of stigmas, and more number of pollens geminated on the stigma, leading to higher seed yield when the line was crossed with a restorer rice line
Summary
Using “two-line method” to produce hybrid rice (Oryza sativa L.), namely, a hybrid produced by a photothermosensitive genic male sterile (PTSGMS) line crossed with a restorer line, could produce great heterosis (Yang et al, 2003; Deng et al, 2013; Ma and Yuan, 2015; Yuan, 2017). For a PTSGMS rice line that shows total male sterility when temperature is >23 or 24◦C (Yuan, 1997; Ma and Yuan, 2015; Mou, 2016), HT stress during anthesis mainly impairs spikelet opening and reduces pistil activity and seriously decreases grain yield of a hybrid produced by the line crossed with a restorer line (Zhu, 2016; Chen et al, 2020, 2021; Yang et al, 2020)
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