Abstract
Low spring temperatures often occur during the winter wheat booting stage, when the young ears are very sensitive to cold. In this study, we used two wheat varieties differing in cold sensitivity (sensitive variety Yangmai 18 and tolerant variety Yannong 19) to examine the effect of low temperature on wheat grain number at booting stage. Low temperature stress was simulated in an artificial climate chamber at 4°C for 60 h in 2016 and at 2, 0, or −2°C for 24 h in morphological assays, showing that the development of wheat spikelets was inhibited and floret growth was delayed following low temperature stress. However, an increase in the sucrose content of young panicles was also observed, and the activity of enzymes involved in sucrose metabolism was dynamically altered. Sucrose phosphate synthase activity was enhanced, and sucrose synthase activity significantly increased after treatment at 4 and 2°C, respectively. However, activities of sucrose synthase and invertase decreased with a reduction in temperature. Gene expression assays further revealed downregulation of TaSuS1 expression and upregulation of TaSuS2, while expression of CWINV was inhibited. Moreover, phytohormone content assays showed an increase in the content of abscisic acid in young wheat ears, but a decrease in the content of auxin and gibberellins. The grain number per spike and 1000-grain weight also showed a downward trend following low temperature stress. Overall, these findings suggest that low temperature at booting induces abscisic acid accumulation in winter wheat, altering the activity of the enzymes involved in sucrose metabolism, which leads to an accumulation of sucrose in the young ears, thereby having a negative effect on wheat production.
Highlights
The smallest ears were observed after treatment at −2◦C. These findings suggest that Low temperature (LT) stress at booting hinders the development of wheat spikelets
The changes in SPS, SuS and, Inv activity in relation to sucrose metabolism under cold stress are not completely consistent between studies, our findings suggest that wheat ears accumulate a large amount of sucrose during adaptation to adapt to LT stress
Our findings suggest that LT stress at booting delays the development of wheat spikelets and florets by increasing the sucrose content of the young ears and altering sucrose metabolism-related enzyme activity and gene expression
Summary
Low temperatures in spring generally occur between the end of March and beginning of April, during which time wheat ears are in a critical period of meiosis and tetrad formation and are, highly sensitive to temperature stress. If exposed to low temperature at this time, the entire wheat spike or parts of the spikelet will fail to set after tassel formation, decreasing yield by 30–50% (Zhang et al, 2011). Significant deterioration in the wheat florets occurs, and pollen development enters the meiosis stage, and the most cold-sensitive period (Slafer et al, 2001). Low temperatures induce abnormal pollen and ovule development, resulting in a reduction in anther size and fertile pollen grains, thereby decreasing the rate of seed setting (Thakura et al, 2010). In the early stages of pollen development, anthers are the strongest metabolic pool, and large amounts of sugars are transported to the anthers to support development (Castro and Clément, 2007). Serrago et al (2008) revealed a positive correlation between basal spikelet gestation floret and the dry weight, as well as carbohydrate content at flowering, suggesting that the supply of assimilates determines the number of fertile florets
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