Physiological changes involved in the acquisition of seed vigor during maturation of sunflower seed

Maturity is an important factor in regulating seed vigor, while inappropriate harvest date affects seed vigor seriously. Here we reported that the seed vigor was the highest among 25–28 days after pollination, and these days were the best harvest time for sunflower seeds. Seed moisture content increased first and then decreased, while seed dry weight increased continuously with the advancement of seed development. Oil and protein are the main nutriments in mature sunflower seeds and changes in both contents were consistent with the seed dry weight. For antioxidases, the activity of ascorbate peroxidase (APX) was decreased gradually before seed maturity. Compared to gibberellin (GA), whose content decreased, abscisic acid (ABA) accumulated first and then decreased during the seed development. Moreover, the content of spermidine (Spd) increased continually, although no regularity of variation was found in putrescine (Put) and spermine (Spm). Further analysis showed that the activities of GA3ox and GA20ox, NCED and ABA8ox, SAMDC and SPDS and corresponding genes expression resulted in changes of GA, ABA and Spd accumulation, respectively. In addition, seed moisture, soluble sugar, GA, ABA content and APX activity were significantly negatively correlated with seed vigor indexes, while seed dry weight, oil, protein and Spd content were significantly positively correlated with seed vigor indexes. These metabolic processes may be closely related to seed vigor formation, and can be used to predict seed vigor.