Effects Ofartificialaging On The Seed Vigor Of Maize

The vigor of maize line seeds,Yu-dan 701 and Yu-dan 901,treated by artificial aging (45℃,100% RH) was studied, and the expression of GA20oxgene andα-amylase genes were tested by semi RT-PCR at 3 days after germination. The results were as follows:1 The seedling performance of aged maize in fieldThe germination rate and seedling height were surveyed at 21 days after field planting. The results showed that the germination speed was low,the germination rate and seedling height had a decreased tendency with the increasing of the ageing time. The healthy degree of seeding was poor, and even could not sprout in field.2 Standard germination experiments of aged maize in laboratoryThe results of standard germination experiments showed that germination rate, germination index and vigor index had a dropping tendency with the increasing of the ageing time. The vigor index dropped significantly after aged 2 days, and germination rate, germination index and vigor index declined, reached to significant level after aged 4 days. The seed vigor of two lines was lost seriously, germination rate, germination index and vigor index reached to 0 after 8-10 d artificial aging treatment.3 Test of aleurone layer vigor of aged maizeEnzyme assays of aleurone layer vigor was analyzed using Yu-dan 701 seeds aged 8 days, the result showed that aging treatment resulted in aleurone layer cells vigor decreased. This seeds is difficult to produceα-amylase even if induced by exogenous GA and indicated that the vigor of aleurone layer cells may have been lost.4 Test of embryo vigor of aged maizeUse of TTC staining for the qualitative test of embryo vigor, the result showed that the embryo vigor had a dropped tendency with the increasing of the ageing time. The embryo vigor decreased significantly after aged 6 days, and the embryo vigor nearly completely loss after aged 8-10 days. The TTC quantitative test was consistent with qualitative test, indicated that the decline of aged seeds vigor may be due to the result of embryo and aleurone layer interaction.5 Changes of membrance permeability and lipid peroxidation of aged maizeRelative conductivity rate of maize seeds'exosmic liquor, O2?ï¿£production rate and malondialdehyde (MDA) content were increased with the increasing of the ageing time. O2?ï¿£production rate and MDA content were increased at early germination then slightly decrease, however, these index were increased during the germination for seeds of aged 8-10 days. The result showed that the damage caused by aging may be repaired during the germination. Relative conductivity rate, O2?ï¿£production rate and MDA content had negative correlation with the germination index. It is reasonable to suggest that membrance permeability and lipid peroxidation may play an important role in the aging of maize seeds.6 Changes of oxidoreductaseactivity of aged maizeOur study showed that the activity of SOD, POD, CAT were decreased with the increasing of the ageing time. Except of aged 8-10 days seeds, the activities of SOD and CAT were increased at early germination then slightly decrease, POD was increased during the germination, showed that the damage of oxidoreductasecaused by aging may be repaired during the germination. The activity of SOD, POD and CAT were positive correlation with the germination index, and negative correlation with relative conductivity rate, O2?ï¿£production rate and MDA content. The result also showed that as the activity of oxidoreductasedecrease, the O₂^.-and H₂O₂ were not eliminated timely, then membrance permeability and lipid peroxidation strengthened, finally the seeds vigor loss.7 Changes ofα-amylase activity of aged maizeThe test ofα-amylase activity showed thatα-amylase activity had a declined tendency with the increasing of the ageing time. At the beginning of the germination the activity ofα-amylase increased significantly, and ascend to the highest point at germination 4 days, then dropped sharply. The activity ofα-amylase was positive correlation with germination rate, germination index and vigor index. So we suggested thatα-amylase activity may be an important physiological index to reflect seed vigor.8 Related genes express of aged maize seedsWe tested the expression of GA20ox andα-amylase genes of the aged seeds using semi-quantitative RT-PCR technique, the results show that these genes expression showed a dropping tendency with the deepening of seed aging. Indicated that aging treatment made GA20ox gene expressed lower, resulted in GA synthesis is reduced, then the expression ofα-amylase gene decline, lead toα-amylase activity reduced, ultimately affect the seed vigor. Seed aging is a series complex changes of cellular structure and physiological function, including membrane structure damage, plasmalemma peroxidation increased, enzyme activity decreased, even the change of genetic basis. These factors interconnected cause-and-effect, eventually leading to the seed vigor decrease. K...