Seed Dormancy Cause And Its Release Mechanism In Chionanthus Retusus

The physiological mechanism of seed dormancy and germination has always been one of the hot issues in the field of plant physiology.The diversity of seed plants in evolution determines the diversity and complexity of the physiological mechanisms of seed dormancy and germination.Therefore,the thorough elucidation of this hot issue depends on the accumulation of specific studies on the dormancy and germination mechanism of various types of seeds.Chionanthus retusus is one of the only two species of Chionanthus in Oleaceae,which has important research value in Systematic evolution.Studies have shown that C.retusus seeds have double dormancy of radicle and epicotyl,but the reason for dormancy and the physiological mechanism of dormancy release are still unclear.In this study,fresh and mature C.retusus seeds were used as experimental materials,taking fresh and mature C.retusus seeds as the research object,the causes of radicle dormancy of C.retusus seeds were analyzed through seed water absorption curve determination,excised embryo culture,endocarp removal,cold/warm moist stratification and dry storage.Then,the seeds with sprouting roots after removing the endocarp were divided into three groups according to the root length,and the dormancy of epicotyl was relieved by removing endosperm,cold/warm stratification and GA₃ seed soaking respectively.Finally,taking the rooting seeds with root length longer than 3 cm treated by cold moist stratification for different times as materials,the contents of reactive oxygen species,non enzymatic antioxidants and antioxidant enzyme activities,as well as the contents of endogenous plant hormones ABA and GA were determined in radicle,endosperm and germ,in order to further explore the causes of epicotyl dormancy and its physiological mechanism.The main conclusions are as follows:（1）The seeds of C.retusus（actually fruit with hard endocarp）have physical dormancy.Its endocarp had a significant inhibitory effect on seed water absorption.（2）The seeds of C.retusus have physiological dormancy.Excised embryos could not germinate into seedlings under culture conditions.Dry storage（30°C）treatment and warm moist stratification（20°C）treatment could promote root germination of intact seeds,but the root germination rate was not high.Cold moist stratification（5°C）treatment had no significant effect on the release of dormancy of intact seeds.（3）The seeds of C.retusus have deep simple epicotyl morphophysiological dormancy,and the release of epicotyl morphophysiological dormancy is affected by the growth length of radicle.Endosperm removal and cold moist stratification could significantly promote the release of epicotyl dormancy of rooting seeds.Among them,the germination rate of rooting seeds with root length longer than 3 cm was the highest after 120 days of cold moist stratification treatment;warm moist stratification treatment and GA₃ solution soaking treatment had no significant effect on the release of epicotyl dormancy.（4）The content of reactive oxygen species,the content of non-enzymatic antioxidants and the activity of antioxidant enzymes in radicle,embryo and endosperm showed significant changes in the process of releasing the dormancy of epicotyl after cold moist stratification treatment,and these physiological indexes in radicle were changed more significantly than those in embryo and endosperm.These results seem to suggest that reactive oxygen species may weaken the role of endosperm through moderate oxidation,and may also play an important role in signal transduction of dormancy release;most of the reactive oxygen species produced in the radicle are probably transported to the embryo,which together with the reactive oxygen species produced by the embryo promote the release of epicotyl dormancy;At the same time,in this process.In the germ,it is likely that the non-enzymatic antioxidants may play a fine role in regulating the amount of reactive oxygen species.In the radicle,it is likely that the antioxidants play a fine role in regulating the amount of reactive oxygen species,so as to ensure that the reactive oxygen species do not cause oxidative damage.（5）In the process of releasing the dormancy of epicotyl by cold and wet stratification,The contents of ABA and GA in radicle and germ changed significantly,and they showed different change patterns.Compared with radicle,ABA content in germ decreased and total GA content increased faster,and the changes of GA species and relative content of each GA were more complex.These results suggest that ABA and GA may have a more complex physiological mechanism in the regulation of epicotyl dormancy of C.retusus seeds...