Studies On Mechanism Of Seed Vigor Formation And Dormancy In Maize

The process of seed vigor formation in Nongda 108, Zhengdan 958, Taiyu 2 and Ludan 50 was investigated. The relation of seed vigor between hybrid seeds and inbred was also studied, and the change of enzymes activity, hormone and storage materials during the formation of seed vigor were investigated. The change of dormancy of fresh maize seed during development, the reason of dormancy and the role of drying in the transition from seed development to germination were investigated. Main results obtained were as follows:Seed moisture declined and seed dry weight increased during development. Maximum seed fresh weight occurred at physiological maturity (PM), and fresh weight decreased after PM. Seed vigor formed during seed development. Coincident with the acquisition of tolerance to desiccation the seed gained the capacity to germinate in 15 days after pollination. Seeds were not able to achieve normal post-germinative growth until 25 days after pollination, because storage deposition was very poor before 25 days. Vigor index increased following the development of seed, and maximum vigor index was occurred at physiological maturity. At the same stage, variety of larger size (Zhengdan 958) had higher vigor than variety of smaller size (Nongda 108). Vigor index of hybrid was higher than parents, so there was high heterosis on seed vigor. There were positive correlations between hybrid's vigor and parents'vigor. Reactive-Oxygen-Scavenging Enzymes activity declined firstly, and increased afterward during seed vigor formation. Hormone also changed to regulate the development of seed. Storage deposition was the foundation of seed vigor formation. Following the development of seed, storage increased and vigor increased.Fresh maize seeds were dormant in any development stage, and genotype influenced fresh seed dormancy and germination. A significant decline in germination of Ludan 50 was observed after 40-45 days, but germination of other varieties increased all the time. Respiration was the most important limiting factor of fresh seed dormancy. Seeds without seed coat and aleurone layer germinated, but could not grow to normal seedling until finishing some metabolism. Drying could break fresh seed dormancy, but the effect of treatment with GA3 and H2O2 was not very significant.Drying was important for the acquisition of germinability, and drying induced precocious maturation and played some role in the transition from a development programme to a programme oriented towards germination and growth. During the desiccation period, germination percentage increased with the decrease of moisture content. Drying could change either the chemical or physical properties of the seed coat to allow a higher rate of gaseous exchange. After drying, the ratio of GA3 to ABA increased, and there were a series of complicated metabolism. Reactive-Oxygen-Scavenging Enzymes activity of drying seeds could resume faster than fresh seed and some proteins relate to germination were synthesized. Increasing the time of germination, fresh maize seed also could germinate. So desiccation was not an absolute requirement for germination of fresh maize seeds, and desiccation just accelerated the transition from seed development to germination.