Differential Sensitivity of Photosynthetic Electron Transport to Dark-Induced Senescence in Wheat Flag Leaves.

Background: In winter wheat (Triticum aestivum), delayed senescence of the flag leaf is linked to the duration of photosynthesis and grain yield. In different wheat cultivars, various components of the photosynthetic apparatus may display differences during senescence. Furthermore, previous studies related to senescence mostly used a limited number of cultivars, making it difficult to investigate the patterns and reasons for different appearance of damage to electron transport among various cultivars.To tackle these challenges, flag leaves of 32 wheat cultivars were subjected to darkness in vitro to simulate the senescence process. The cultivars were divided into three groups by k-means clustering, based on the rate of decline in their leaf chlorophyll content. Subsequently, we simultaneously measured prompt chlorophyll a fluorescence, delayed chlorophyll a fluorescence, and modulated 820-nm light reflection to examine the alterations in photosynthetic electron transport within the three groups of wheat cultivars during dark-induced senescence.

Results: The results showed that the photosystem II (PSII) donor side, grouping of PSII units, PSII reaction center, PSII acceptor side, and photosystem I (PSI) were all damaged during dark-induced senescence, while the sensitivity of photosynthetic electron transport to senescence gradually increased from the upstream to downstream electron carriers on the PSII acceptor side. The extent of the observed decrease in activity of the different components of the photosynthetic electron transport chain during senescence, was consistent with the chlorophyll degradation rate of the wheat cultivars, while the priority of inhibition for different photosynthetic electron transport processes in each cultivar group was different. The results from the three separate signals align well with each other.

Conclusions: The sensitivity of different part of photosynthetic electron transport to senescence were varied depended on their chlorophyll degradation rate. The differences in the response of different processes of photosynthetic electron transport to chlorophyll degradation rates might be an important factor influencing the differences in photoinhibition among wheat cultivars, especially in senescence process.