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Decrease in the grain yield resulted from a low percentage of opened spikelets under high temperature (HT) during anthesis is a serious problem in the seed production of photo-thermo-sensitive genic male sterile (ptGMS) rice (Oryza sativa L.) lines, and the mechanism is little understood. elucidating the physiological mechanism underlying the effect of HT during anthesis on spikelet-opening of PTGMS lines would have great significance in exploring the effective way to mitigate the adverse effect of HT. In this study, two PTGMS lines and one restorer line of rice were used and were subjected to normal temperature (NT) and HT treatments. The results showed that, compared with NT, HT significantly decreased the percentage of opened spikelets, fertilization percentage and seed-setting by significantly increasing the percentage of wrapped spikelets and reducing the spikelet-opening angle, length of spikelet-opening time. The HT significantly decreased the contents of soluble sugars, jasmonic acid (JA) and methyl jasmonate (MeJA) in the lodicules before and at glume-opening, which were significantly correlated with and accounts for the low percentage of opened spikelets under HT for rice, especially for the ptGMS lines.Male sterility in cereals has played a critical role in the utilization of heterosis by facilitating hybrid breeding and greatly contributed to the increase in productivity for many crops such as rice (Oryza sativa L). The establishment of the breeding theory and technology of the "two-line method" hybrid rice (hereinafter referred to as the two-line hybrid rice), especially photo-thermo-sensitive genic male sterile (PTGMS) rice lines, is another major scientific and technological innovation in the utilization of heterosis after the "three-line method" hybrid rice application 1-7 . Compared with three-line hybrid rice with nuclear-plasma interaction pollen sterility as the core technology in a hybrid rice system, two-line hybrid rice can easily maintain sterile line production without using maintainer lines. Moreover, two-line hybrid rice also has many other advantages, such as a wider range of germplasm resources which can be used as breeding parents, greater heterosis, and simpler procedures for breeding and hybrid seed production 2,3,7-10 . Today, the annual planting area of two-line hybrid rice in China has exceeded 5 million hectares, which has become a main way using heterosis in rice 3,11-15 . However, the fertility of PTGMS rice line is easily affected by temperature and light. Usually, the PTGMS rice line tends to produce low purity of hybrid seeds due to self-cross at a low temperature (23-24 °C) in the seed production. The spikelets of PTGMS lines during anthesis could not open normally at high temperature (HT, ≥35 °C), which seriously reduces the hybrid seed yield 2,3,[11][12][13]16 .Temperature is an important ecological factor for plant growth. HT (≥35 °C) could seriously influence the growth and development of rice, at either vegetative or reproductive growth stage [17][18][19][20][21] . W...

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.

Rising levels of atmospheric carbon dioxide (CO2) could, potentially, be exploited as a means to increase seed yield and maintain food security, especially for cereal grains. Although there have been multiple cultivar trials indicating that significant yield variation occurs, the basis for these differences has not been entirely elucidated. Here, we focus on two rice cultivars that differed in field trials to their yield sensitivity to elevated CO2: Yangdao6hao (YD6), and Wuyunjing23 (W23) to assess whether observed yield differences (YD6 > W23) were associated with concurrent changes in leaf‐level characteristics. At ambient levels of CO2, leaf net photosynthesis (A) of YD6 was compatible with that of W23. However, at elevated CO2, A was higher for YD6 relative to W23. The stability of leaf Rubisco content, biochemical characteristics (Vc,max, and Jmax), nitrogen enzymatic activity, and chlorophyll concentration differed significantly, with greater values observed for YD6 relative to W23 at elevated CO2. While such results are consistent with other studies, we also demonstrate that a higher ratio of carbon sinks (seed) to carbon sources (leaf), were linked to increases in cytokinins, and slower flag leaf senescence for the YD6 relative to the W23 cultivar at elevated CO2. While additional data for a broader genetic selection are needed, the current study suggests a link between source/sink carbon assimilation, maintenance of photosynthetic biochemistry, and slower leaf senescence for rice cultivars that show a stronger yield response to projected CO2 levels. This information, in turn, may provide suitable metrics for future CO2 selection among rice cultivars.

To explore the effects of an increased CO 2 concentration on the growth and N absorption and utilization of different rice (Oryza sativa L.) cultivars, the Liangyoupeijiu (LY) and Nanjing 9108 (NJ) rice cultivars were grown under ambient CO 2 (400 μmol mol −1) and elevated CO 2 (600 μmol mol −1) combined with high N (2.5 mM) and low N (0.5 mM) treatments. The effects of elevated CO 2 on root morphological and physiological characteristics, N uptake and utilization, and dry matter accumulation and distribution were analyzed. The results showed that the elevated CO 2 levels significantly increased the total biomass of LY under different N levels but only significantly increased the total biomass of NJ under high N. Elevated CO 2 significantly increased the N concentrations in the organs of LY but had no significant effect on the N concentrations in the organs of NJ. As a result, elevated CO 2 significantly increased the N accumulation of LY but decreased the N uptake of NJ under low N. Under elevated CO 2 conditions, the total root length and root surface area of LY increased, and the roots also maintained high activity. The larger roots and higher physiological activity and N accumulation of LY were the important reasons for the high levels of dry matter production in response to elevated CO 2. Improvements in the root morphology and physiological activity of rice in future breeding efforts should enhance the dry matter production of low-response rice.