Abstract:

【Background】High-vigor seeds germinate quickly and efficiently, and they are highly stress resistant and advantageous during crop production. Diethyl aminoethyl hexanoate (DA-6), as a tertiary amine plant growth regulator, increases plant photosynthetic rates, regulates carbon and nitrogen metabolism and improves crop quality and yield. However, there are limited studies on its effects on seed vigor. 【Objective】This study analyzed the effects of spraying DA-6 post-flowering on the compounds accumulated in grains, expression levels of key genes associated with metabolism and stress-resistance, 1000-grain weights, chemical compositions and seed vigor to determine DA-6’s mechanism for regulating wheat seed vigor, which has important theoretical and practical significance in the production of high-vigor wheat seeds. 【Method】Wheat varieties, Liangxing 77 and Shannong 23, grown in fields of the Mazhuang Experimental Base of Shandong Agricultural University in 2017-2018 and 2018-2019 (117°E, 36°N) were sprayed with DA-6. Two treatment concentrations (0 and 6 g·L^-1 DA-6), two treatment periods (2 and 6 days after anthesis) and three zone groups, each having an area of 6 m × 3 m, were used. Fresh samples of grains, stems below spikes and flag leaves were collected at the early and middle stages of grain filling (12 and 22 days after anthesis, respectively), and the expression levels of key metabolism-related enzymes were analyzed. Samples were taken on different days of grain development (25, 30, 35 and 40 days after anthesis), and the 1000-grain weights, protein contents and starch contents were determined after natural drying and threshing. For wheat spikes harvested at the maturity stage, the germination and vigor indices of the whole ear, different spike positions (upper, middle and lower) and different grain positions (lower and upper grain) were measured. 【Result】Spraying 6 g·L^-1 DA-6 at 6 days after anthesis significantly increased the 1000-grain weights, seed protein contents, and plant dry weights of the upper spikes and upper grains in both wheat varieties, and it significantly improved the seed vigor indices. DA-6 spraying at 6 days after anthesis effectively reduced the seed vigor difference between different spike and grain positions, and it improved the seed vigor of different spike and grain positions in wheat as a whole, especially those of upper and middle spikes, as well as the upper grain. However, DA-6 spraying at 2 days after anthesis significantly reduced seed vigor, 1000-grain weights and seed protein contents. The 1000-grain weights of Liangxing 77 and Shannong 23 increased first and then decreased as the grain-filling period was extended. However, relative and absolute protein contents increased with time. Additionally, both varieties showed the highest 1000-grain weights and protein contents after spraying 6 g·L^-1 DA-6 at 6 days after anthesis. While the 1000-grain weight of Liangxing 77 was not significantly different from that of the control group, the relative and absolute protein contents were significantly greater. The 1000-grain weight and absolute protein content of Shannong 23 significantly increased after spraying 6 g·L^-1 DA-6 at 6 days after anthesis. DA-6 spraying at 2 days after anthesis had no significant effects on 1000-grain weights, relative and absolute protein contents or starch contents. Real fluorescence quantitative PCR showed that DA-6 spraying at 6 days after anthesis significantly increased the expression levels of protein phosphatase and sucrose phosphate synthase in flag leaves. The expression levels of class I heat shock protein (hsp) and hsp70 in the stem, like those of protein disulfide isomerase and hsp82 in grains, increased significantly. The α-amylase activity during seed germination was measured in samples sprayed with DA-6 at 6 days after anthesis. The activity gradually increased along with germination time in both control and treated Shannong 23. DA-6 spraying at 6 days after anthesis significantly increased the α-amylase activity levels in seeds of both varieties after germinating for 72 h. 【Conclusion】Spraying DA-6 at 6 days after anthesis promoted the expression levels of proteins, key enzyme-encoding genes of sucrose metabolism and hsps. It also facilitated the synthesis of seed storage substances, increased the protein contents of seeds and significantly increased the 1000-grain weights. The dry weight of individual plants during germination and seed vigor of upper, middle spikes and the upper grain of harvested seeds in two varieties significantly improved after spraying DA-6. The seed vigor difference between different spike positions decreased, and the α-amylase activity increased during seed germination. Thus, spraying DA-6 after anthesis promoted the accumulation of seedling dry matter and improved material transformation capacities during seed germination. Additionally, seed vigor improved. Our studies suggest that spraying 6 g·L^-1 DA-6 on wheat at 6 days after anthesis is an effective way to improve seed vigor.

Key words: wheat, DA-6, seed vigor, real-time PCR