Abstract:

Objective: This study aims to explore the effects of artificial dehydration on the viability and germination characteristics of Phoebe bournei seeds, so as to provide basis for understanding the mechanism of seed viability reduction and germination restriction of P. bournei seeds. Method: The physiological and biochemical characteristics as well as gene expression of seeds with four different water contents of 40% (no dehydration), 30% (mild dehydration), 20% (moderate dehydration) and 10% (severe dehydration) were analyzed through artificial dehydration treatment, to reveal the effects of different dehydration degrees on P. bournei seed viability and germination rate. Result: It was found that the seed viability of P. bournei first increased and then decreased with the increase of dehydration. The germination rate of seeds with mild dehydration (30% water content) was up to 93%, which was even higher than that of non-dehydrated seeds. Severe dehydration (10% water content) led to the increase of malondialdehyde (MDA) content, indicating that the degree of seed membrane lipid peroxidation increased with the increase of dehydration. Peroxidase (POD) activity first increased with increasing dehydration, but decreased significantly when seed water content reached 10%. When P. bournei seeds stored in 25 ℃ and humidity environment, mold rate of seeds with 30% and 40% water content was about 58%, while severe dehydrated seeds were all moldy. The expression analysis of key genes involved in P. bournei seed germination showed that the negative regulatory transcription factor PbABI3 was down-regulated during seed germination. The expression of PbFUS3 and PbLEC2 genes was significantly up-regulated at the early stage of radicle growth in seeds with 30% water content, but not in seeds with 40% water content. Conclusion: P. bournei seed does not tolerate dehydration, the viability of seeds increases first and then decreases with increasing dehydration. The germination rate of moderately dehydrated (20% water content) or severely dehydrated (10% water content) seeds decreases significantly. During severe dehydration, the POD activity in the seeds reduces and the seeds are subjected to oxidative damage. The change of seed water content can induce the activity of antioxidant enzyme system in P. bournei, and affect seed germination by regulating the specific expression of key genes PbABI3, PbFUS3 and PbLEC2 involved in the seed germination.

Key words: Phoebe bournei, seed germination, desiccation tolerance, gene expression