Morphology And Physiology Response To Cold During Seeds Epicotyl Dormancy Breaking Of Paeonia Emodi

Paeonia emodi has the advantages of producing tall plants,thick stalk and a high seed yield,and is an important germplasm resource.Due to its narrow distribution range,it has not been fully exploited at present.Reproductive biology research is the premise of resource utilization.The Paeonia genus seeds need cold stratification to break epicotyl dormancy after rooting.Compared with other wild herbaceous peonies,P.emodi takes longer time to break the epicotyl dormancy of seeds,and the reason is not clear.In order to explore the propagation method and the mechanism of dormancy breaking in P.emodi seeds,the differences of nutrient metabolism and endogenous hormones regulation between P.emodi and P.lactiflora seeds during cold stratification are researched.The purpose is to explore the reasons of epicotyl dormancy of P.emodi seeds.The main results are as follows.1.P.emodi seeds are obviously different from other herbaceous peonies in morphology and size,but their internal structure is similar.The seeds can absorb water through seed holes and epidermis,so the seed coat is not the barrier to exchange water and air with the outside.There are some substances in seed coat,endosperm and embryo inhibiting seed germination.The type of seed dormancy belongs to deep simple epicotyl morphophysiological dormancy.Removal of the seed coat and endosperm can shorten the rooting time by 35 days,but fails to break the epicotyl dormancy.The epicotyl dormancy of P.emodi seeds can be broken by cold stratification at 4°C for 110 days.After cold stratification for 90 days,the seeds are soaked in 300-500 mg/L GA₃ solution for 24 hours at room temperature,which can advance the start time of seedling emergence by 16-19 days.The epicotyl dormancy cannot be broken by GA₃treatments without cold stratification.2.During 4°C cold stratification,the germ of P.emodi elongated at the 10th week,4 weeks later than that of P.lactiflora.Starch,soluble sugar and soluble protein are the main energy sources,which are the same as those of P.lactiflora.However,the obvious consumption of starch appears at the early stage of cold stratification in P.emodi,which is earlier than that of P.lactiflora.The reduction of soluble sugar and soluble protein appears at the later stage,which is later than that of P.lactiflora.The content changes of the three nutrients in P.emodi are greater than those of P.lactiflora,which indicates that breaking the epicotyl dormancy of P.emodi seeds need more nutrients consumption than that of P.lactiflora.3.The activity of nutrient metabolism enzymes in P.emodi seeds is generally higher than that of P.lactiflora during cold stratification.The activities ofα-amylase,β-amylase and lipase are significantly higher than before cold stratification,and the activity of acid protease is also significantly higher at the12th and 14th weeks.Theα-Amylase activity of P.emodi seeds during cold stratification is significantly correlated with starch content,acid protease activity is significantly correlated with soluble protein content（P<0.05）,but this phenomenon is not found in P.lactiflora.It indicates that there may be differences in the metabolic pathways of nutrients between P.emodi and P.lactiflora seeds.4.During the cold stratification,the content of ABA,GA₃,IAA,ZR,JA-Me,BR and the ratio of ABA to GA₃ in P.emodi seeds change significantly compared with that before cold stratification,and the changes of the six hormones were different from P.lactiflora.The changes of GA₃ and IAA content in P.emodi seeds are greater than those of P.lactiflora;the changes of ABA,ZR,JA-Me,BR content is smaller than that of P.lactiflora.In addition,different hormones have different response time to cold in P.emodi seeds,and the key changes of all six endogenous hormones in P.emodi are later than those in P.lactiflora.5.During the cold stratification,the genes BZR/BES1,JAZ and MYC related to hormone signal transduction respond to cold in P.emodi seeds are more consistent with those in P.lactiflora seeds,showing up-regulated and down-regulated expressions.Those indicate that BR and JA-Me have similar regulatory effects in P.emodi and P.lactiflora in the process of cold stratification.PYL,Sn RK2,GAI,GID1 gene expression were different in P.emodi and P.lactiflora.That indicate that there are some differences endogenous hormones response patterns to cold stratification in P.emodi and P.lactiflora.This study clarifies the seed dormancy and germination characteristics of P.emodi and the important role of cold in the process of epicotyl dormancy breaking.In the process of cold stratification,the relationships between starch,soluble sugar,soluble protein and amylase,acid protease,and lipase activities in P.emodi seeds are different from that of P.lactiflora,and the expression of PYL,Sn RK2,GAI,GID1 genes related to hormone signal are also different from P.lactiflora.And those differences in response to cold stratification could be one of the reasons of the epicotyl dormancy breaking of P.emodi seeds need longer cold stratification time.