Effects of Post-silking Shading Stress on Enzymatic Activities and Phytohormone Contents During Grain Development in Spring Maize

摘要

Low sunlight intensity from mid-June to mid-July in Southern China is the primary environmental factor that affects maize grain development. A field trial was conducted in 2016-2017 to investigate the effects of post-silking shading (i.e., 30% and 50% light deprivation using black net covers; ambient light as control) on grain filling, abscisic acid (ABA), and indole-3-acetic acid (IAA) contents, starch and protein contents, and enzymatic activities involved in biosynthesis by using two maize varieties, namely, the shade-sensitive Zhengdan958 (ZD958) and the shade-resistant Suyu30 (SY30). Results showed that grain filling was negatively affected by shading. Under 30% and 50% shading conditions, grain dry weight decreased by14.6% and 29.6% for ZD958, respectively, and 10.8% and 15.1% for SY30, respectively. Shading improved protein content, but restricted starch deposition. The activities of starch and protein synthetic enzymes were downregulated by shading, and the effect was severe when the plants were subjected to greater light deprivation (from 30 to 50%). Shading decreased IAA content, but increased ABA content. Under shading conditions, SY30 had higher activities of glutamine synthetase, sucrose synthase, and soluble starch synthase than ZD958. Moreover, SY30 generally had a higher IAA content, but lower ABA content than ZD958. These properties favored starch accumulation and increased grain weight. In conclusion, post-silking shading decreased IAA content and weakened the activities of starch and protein syntheses, but increased ABA content. These conditions restricted starch deposition, thereby resulting in grain weight loss.