No abstract

Drought stress during grain filling is the most yield-damaging to wheat. Pre-drought priming facilitated the wheat plants to sustain grain development against the post-anthesis drought stress by modulating the levels of growth hormones. Post-anthesis drought stress substantially reduces grain yield in wheat (Triticum aestivum L.) due to impaired grain development associated with imbalanced levels of growth hormones. To investigate whether pre-drought priming could sustain grain development in wheat by regulating favorable levels of growth hormones under post-anthesis drought conditions, the plants of a drought-sensitive (Yangmai-16) and drought-tolerant (Luhan-7) wheat cultivar were exposed to a moderate drought stress during tillering (Feekes 2 stage) for priming, and then, a subsequent severe drought stress was applied from 7 to 14 days after anthesis. The results showed that drought-stressed plants of both cultivars showed a decline in flag leaf water potential, chlorophyll contents, photosynthetic rate, grain size initiation, and grain filling as compared to well-watered plants; however, decline in these traits was less in pre-drought primed (PD) plants than in nonprimed (ND) plants. Under drought stress, the PD plants regulated higher concentrations of zeatin and zeatin riboside, indole-3-acetic acid, gibberellins, and lower abscisic acid content in grains, resulting in higher endosperm cell division and expansion, grain size initiation, grain-filling rate and duration, and finally higher grain dry weights as compared to ND plants. The PD plants of both cultivars showed higher potential to tolerate the post-anthesis drought stress, but more effect was displayed by drought-tolerant cultivar. From the achieved results, it was concluded that pre-drought priming facilitated the wheat plants to sustain higher grain development and yield against the most yield-damaging post-anthesis drought stress by modulating the levels of growth hormones.

Inhibited photosynthesis caused by post-anthesis high-temperature stress (HTS) leads to decreased wheat grain yield. Magnesium (Mg) plays critical roles in photosynthesis; however, its function under HTS during wheat grain filling remains poorly understood. Therefore, in this study, we investigated the effects of Mg on the impact of HTS on photosynthesis during wheat grain filling by conducting pot experiments in controlled-climate chambers. Plants were subjected to a day/night temperature cycle of 32°C/22°C for 5 days during post-anthesis; the control temperature was set at 26°C/16°C. Mg was applied at the booting stage, with untreated plants used as a control. HTS reduced the yield and net photosynthetic rate (Pn) of wheat plants. The maximum carboxylation rate (VCmax), which is limited by Rubisco activity, decreased earlier than the light-saturated potential electron transport rate. This decrease in VCmax was caused by decreased Rubisco activation state under HTS. Mg application reduced yield loss by stabilizing Pn. Rubisco activation was enhanced by increasing Rubisco activase activity following Mg application, thereby stabilizing Pn. We conclude that Mg maintains Rubisco activation, thereby helping to stabilize Pn under HTS.

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