Incidence of cold during early stages is an obstacle for the growing progress of rice plants. Cold stress has strong negative effects on photosynthetic activity. Previously, our group evaluated plant survival of 90 indica rice genotypes after cold treatment. Two sister lines were characterized as cold-tolerant and cold-sensitive. Transcriptomic analyses of the same genotypes had indicated differential expression of genes related to photosynthesis. Previous work with japonica rice had suggested that cold sensitivity was more related to photosystem II (PSII) than to photosystem I (PSI). Using our previously identified contrasting genotypes, we investigated the role of specific steps of the photosynthetic process in cold tolerance/sensitivity of indica rice plants during and after (recovery period) cold exposure. During both cold treatment and recovery period, the photochemical activity (including PSII and PSI) presented higher levels in the low temperature-tolerant genotype, when compared with the sensitive one. The higher photochemical efficiency during the cold treatment appears to be related to a lower fraction of reduced Q⁻_A in PSII. We also observed lower transpiration rates and higher water use efficiency in the cold-tolerant genotype, due to stomatal closure. After the recovery period, the higher efficiency in the cold-tolerant genotype seems to be related to a lower fraction of reduced Q⁻_A and a larger pool of final electron acceptors at the PSI. This work uncovered changes in photosynthetic performance including both photosystems and improved water use efficiency which may be important components of cold tolerance mechanisms in indica rice.

中文翻译：

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耐寒性对比籼稻姐妹系的光合活性。


早期寒冷的发生是水稻生长发育的一个障碍。冷胁迫对光合作用有强烈的负面影响。此前，我们课题组对90个籼稻基因型冷处理后的植株存活率进行了评估。两个姐妹系具有耐冷和冷敏感的特征。相同基因型的转录组分析表明与光合作用相关的基因存在差异表达。之前对粳稻的研究表明，冷敏感性与光系统 II (PSII) 的关系比与光系统 I (PSI) 的关系更大。利用我们之前确定的对比基因型，我们研究了光合作用过程的特定步骤在籼稻植物在冷暴露期间和之后（恢复期）的耐冷性/敏感性中的作用。在冷处理和恢复期间，与敏感基因型相比，耐低温基因型的光化学活性（包括PSII和PSI）均表现出较高水平。冷处理期间较高的光化学效率似乎与 PSII 中较低的 Q ^- _A还原比例有关。我们还观察到，由于气孔关闭，耐寒基因型的蒸腾速率较低，水分利用效率较高。恢复期后，耐冷基因型的较高效率似乎与减少的 Q ^- _A比例较低和 PSI 处最终电子受体池较大有关。 这项工作揭示了光合性能的变化，包括光系统和水分利用效率的提高，这可能是籼稻耐寒机制的重要组成部分。