Abstract
Heat stress causes morphological and physiological changes and reduces crop yield in rice (Oryza sativa). To investigate changes in phytohormones and their relationships with yield and other attributes under heat stress, four rice varieties (Nagina22, Huanghuazhan, Liangyoupeijiu, and Shanyou 63) were grown in pots and subjected to three high temperature treatments plus control in temperature-controlled greenhouses for 15 d during the early reproductive phase. Yield reductions in Nagina22, Huanghuazhan, and Liangyoupeijiu were attributed to reductions in spikelet fertility, spikelets per panicle, and grain weight. The adverse effects of high temperature were alleviated by application of exogenous 6-benzylaminopurine (6-BA) in the heat-susceptible Liangyoupeijiu. High temperature stress reduced active cytokinins, gibberellin A1 (GA1), and indole-3-acetic acid (IAA), but increased abscisic acid (ABA) and bound cytokinins in young panicles. Correlation analyses and application of exogenous 6-BA revealed that high temperature-induced cytokinin changes may regulate yield components by modulating the differentiation and degradation of branches and spikelets, panicle exsertion, pollen vigor, anther dehiscence, and grain size. Heat-tolerant Shanyou 63 displayed minor changes in phytohormones, panicle formation, and grain yield under high temperature compared with those of the other three varieties. These results suggest that phytohormone changes are closely associated with yield formation, and a small reduction or stability in phytohormone content is required to avoid large yield losses under heat stress.
Highlights
Late reproductive phase, non-structural carbohydrates stored in the stems and current assimilates in functional leaves are transported to the panicle and largely accumulate in developing grains[9,11]
The grain yields under high nighttime temperature treatments were reduced by 41% for N22, 56% for HHZ, 62% for LYPJ, and 1% for Shanyou 63 (SY63); under high daytime temperature treatments, grain yields were reduced by 58% for N22, 42% for HHZ, 35% for LYPJ, and 8% for SY63
The largest reductions in grain yield were observed under ADT in all four varieties, with grain yield reduced by 85% for N22, 74% for HHZ, 80% for LYPJ, and 9% for SY63
Summary
Late reproductive phase, non-structural carbohydrates stored in the stems and current assimilates in functional leaves are transported to the panicle and largely accumulate in developing grains[9,11]. Previous studies report that abiotic stresses such as drought, salinity, and chilling adversely affect panicle formation and cause physiological changes in phytohormone levels and photosynthetic activity, which reduces rice yield components[15,16,17,18]. In other crops such as pearl millet, oats, and sunflower, high temperature during the early reproductive phase retards panicle development and growth and reduces grain number, seed set, and grain weight[19,20,21]. Our goal was to elucidate the pathways involved in yield loss due to high temperature conditions during the early reproductive phase
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