Study On The Dormancy And Germination Of Paeonia Rockii Seeds

Paeonia rockii is a woody plant belonging to Paeoniaceae,Paeonia,Section Moutan DC..It is an ornamental and medicinal plant named for aobvious purple areas at the base of petals.Paeonia rockii is the most important original species of the northwest tree peony cultivar group.It is widely cultivated in Gansu Province because of good ecological adaptability.Paeonia rockii seeds are difficult to germinate under natural conditions due to dormancy characteristic,which is the main limiting factor of breeding and large scale production.The study used Paeonia rockii seeds as the experimental materials to explore the water permeability of the seed coat,the morphology of seed embryo,the endogenous inhibitory substance of seed coat and endosperm,seeds treated with different concentrations of gibberellic acid?GA₃?to investigate the effects of rooting,rooted seeds treated with different concentrations of GA₃ and different durations of chilling time to investigate the effects of breaking epicotyl dormancy in order to find out the main reason of seed dormancy and the best treatment of breaking dormancy.The results were showed as follows:1.Seed coat of Paeonia rockii could slowed down water absorbing speed,but it had nearly no effects on the final water absorption percentage of seeds.Seed embryo were not fully developed yet when seeds comed to mature morphologically.There were endogenous inhibitory substances to inhibit the seed germination and seedling growth of Brassica campestris both in seed coat and endosperm,and the inhibitory action of endosperm was stronger than that of seed coat in the same concentration.Inhibition by Paeonia rockii aqueous extracts of seed coat and endosperm,the strength on seedling growth of Brassica campestris inhibited principally root length.The inhibitory substances in the seed coat and endosperm cause the changes of antioxidant enzyme activity.So the seed dormancy of Paeonia rockii was morphophysiological dormancy due to embryo only developing partially and endogenous inhibitory substances in seeds.2.GA₃ treatment could effectively promote the rooting of seeds.300 mg/L GA₃treatment was the best to promote rooting with the highest rooting rates of 71.00%and made the first seed rooting time shorter 14.67 days than control treatment.In compared with the control,GA₃ treatment could promote hydrolysis of the starch,soluble sugar accumulation and soluble protein consumption of seeds in the first 15days.It also could accelerate improvement of activity of peroxidase?POD?in the first30 days.During sand stratification process,abscisic acid?ABA?decreased gradually,gibberellic acid?GA?,zeatin riboside?ZR?and indole-3-acetic acid?IAA?increased first and then decreased.In compared with the control,GA₃ treatment could promote the content of GA,ZR and IAA to have significant improvements to dormancy breaking.3.Chilling and GA₃ treatment could shorten first sprouting time,improve germination index and germination rate of rooted seeds.First sprouting time was more significantly affected by GA₃ treatment.Germination index and germination rate were more significantly affected by chilling treatment.Rooted seeds could not germinate without chilling or GA₃ treatment.The chilling time for 21 days combined with 300 mg/L GA₃ treatment and the chilling time for 28 days combined with 200mg/L GA₃ treatment were the most efficient methods to break epicotyl dormancy.First sprouting time,germination index and germination rate had significant differences which were 26.00 days and 26.33 days,0.64 and 0.64,80.00%and 78.89%under two methods.The content of the starch,soluble sugar of seed embryo increased gradually during germination.The content of soluble protein decreased gradually.Chilling and GA₃ treatment could promote the starch and soluble sugar accumulation and soluble protein consumption during pre-germination.Chilling and GA₃ treatment could also promote ABA decreased gradually,GA,ZR and IAA increased during germination.The content of GA had obvious changes by GA₃ treatment.GA₃ treatment could replace chilling treatment to break epicotyl dormancy.Chilling and GA₃ treatment can regulate the content of endogenous hormones and the transformation of nutrients,thus seeds of Paeonia rockii can break dormancy and germinate in advance.