Shading treatment during late stage of seed development promotes subsequent seed germination and seedlings establishment in sunflower

During the sunflower seed production process, the role of artificial shading treatment (ST) in seed development and subsequent seed germination remains largely unknown. In the present study, sunflower mother plants were artificially shaded during 1–34 (full period-ST, FST), 1–22 (early period-ST, EST), and 22–34 (late period-ST, LST) days after pollination (DAP), to examine the effects of parental shading on subsequent seed germination. Both FST and EST significantly reduced the photosynthetic efficiency of sunflower, manifested as decreased seed dry weight and unfavorable seed germination. On the contrary, LST remarkably increased seed dry weight and promoted subsequent seed germination and seedling establishment. LST enhanced the activities of several key enzymes involved in triglyceride anabolism and corresponding-genes expression, which in turn increased the total fatty acid contents and altered the fatty acid composition. During early germination, the key enzyme activities involved in triglyceride disintegration and corresponding-gene expressions in LST seeds were apparently higher than those in seeds without the shading treatment (WST). Consistently, LST seeds had significant higher contents of ATP and soluble sugar. Moreover, enzyme activities related to abscisic acid (ABA) biosynthesis and corresponding gene expressions decreased within LST seeds, whereas the enzyme activities and corresponding gene expressions associated with gibberellin (GA) biosynthesis were increased. These results were also evidenced by the reduced ABA content but elevated GA level within LST seeds, giving rise to higher GA/ABA ratio. Our findings suggested that LST could promote sunflower seed development and subsequent seed germination as well as seedling establishment through modulating the dynamic metabolism of triglycerides, fatty acid and GA/ABA balance.