Morphological And Physiological Changes And Germination Temperature During Stratification Of Pinus Koraiensis Seeds

Pinus koraiensis sieb.et Zucc is one of the most important fruit trees in China and East Asia.In order to explore the possibility of breaking the dormancy by naked stratification and optimize the stratification conditions,determine the dormancy type and the appropriate germination temperature of Pinus koraiensis seeds.In this study,fresh and mature Pinus koraiensis seeds were used as materials,and the morphological indexes,inhibitory activity,germination status and endogenous hormone content of Pinus koraiensis seeds were determined and analyzed in the process of treatment by mixed sand stratification,naked stratification,GA3 immersion treatment and different germination temperatures.The main research results were as follows:(1)At the end of stratification,under the conditions of mixed sand stratification and naked stratification,the embryo length,embryo length/kernel length ratio and embryo dry weight/kernel dry weight ratio with warm treatment all increased significantly,while the embryo length,embryo length/kernel length ratio,embryo dry weight/kernel dry weight ratio did not significantly change under the low temperature treatment.It indicated that warm temperature(20℃)treatment was conducive to the ripening growth of Pinus koraiensis seeds.The seeds of Pinus koraiensis did not germinate after only warm or low temperature treatment,warm temperature to low temperature treatment was helpful to break the dormancy of Pinus koraiensis seeds.Based on the comprehensive analysis of germination percentage,germination index and average germination time,the warm 8 weeks+low 12 weeks treatment under the condition of mixed sand stratification and naked stratification was the best stratification.It showed that naked stratification treatment was feasible to break the dormancy of Pinus koraiensis seeds.The optimal concentration of GA3 solution to soak seeds was 100 mg/L,only before warm temperature or low temperature to soak seeds with 100 mg/L GA3 solution significantly increased the embryo length,embryo length/kernel length ratio,embryo dry weight/kernel dry weight ratio,germination percentage and germination index compared with the control(without GA3 solution),and the germination time was shortened.(2)For each part of the Pinus koraiensis seed inhibitor activity determination found that Cabbage seeds did not germinate in the middle seed coat and seed kernel extract solution of unstratified seeds.After the treatment of naked stratification or mixed sand stratification,cabbage seeds did not germinate in the seed kernel extract solution,the lowest germination percentage in the middle seed coat extract solution was 33%,the highest could reach 57%.The results showed that germination inhibitors still existed in seed kernel and middle seed coat of Pinus koraiensis after stratification treatment,and the activity of inhibitors in seed kernel was significantly higher than that in middle seed coat,the inhibitor that affected the dormancy of Pinus koraiensis seed mainly exists in the seed kernel.(3)The middle seed coat of Pinus koraiensis had a certain water permeability.Warm or low temperature treatment alone could not break the dormancy of Pinus koraiensis seeds,warm treatment was conducive to the ripening growth of red pine seeds and to break the morphological dormancy,while low treatment was beneficial to the release of physiological dormancy.The treatment of soaking seeds by 100 mg/L GA3 solution could promote the growth of seed embryo and increase the germination percentage,but could not replace low temperature stratification.The specific dormancy type of Pinus koraiensis seeds belonged to the deep simple morphophysiology dormancy type.(4)Pinus koraiensis seeds could germinate under the conditions of constant temperature or variable temperature from 5℃ to 30℃.Under constant temperature,the germination percentage of Pinus koraiensis seeds was very low at 5℃,once the temperature exceeded 10℃,the germination percentage significantly increased,but at 30℃,the germination percentage of Pinus koraiensis seeds began to decline.Under variable temperature,the higher the temperature,the better the seed germination.After the treatment of warm 8 weeks+low 12 weeks under mixed sand stratification and naked stratification,the germination percentage,germination index and average germination time of Pinus koraiensis seeds were 81%and 94%,2.98 and 4.31,8.8 and 9.27 days respectively under the 25℃ temperature.Therefore,based on the comprehensive analysis,25℃ was the optimum germination temperature for Pinus koraiensis seeds.(5)The endogenous hormone change trend of endosperm and seed embryo was basically consistent during the stratification.In the process of stratification,the contents of GAs,CTK and their ratios to ABA showed an overall downward trend,and the contents of ABA,IAA,and ETH present the rise trend.The trend of IAA/ABA in endosperm and seed embryo was basically the same,but there was no significant increase or decrease.The overall upward trend of endosperm ETH/ABA ratio in each treatment was not obvious,and the ETH/ABA ratio of seed embryo showed a downward trend.It indicated that GAs and CTK had no obvious effect on dormancy release of Pinus koraiensis seeds,ETH had a promoting effect on breaking dormancy of Pinus koraiensis seeds,ABA was the main regulatory substance of Pinus koraiensis seeds dormancy,and IAA interacted with ABA to regulate seed dormancy.In conclusion,naked stratification to break the Pinus koraiensis seed dormancy completely feasible,soaking seeds with 100 mg/L GA3 solution can improve Pinus koraiensis seed germination percentage,the specific dormancy type of Pinus koraiensis seeds belongs to the deep simple morphophysiology dormancy type,Pinus koraiensis seeds with dormancy breaking suitable germination temperature is 25℃,the embryo growth state,endogenous inhibitor activity and endogenous hormone change is closely related to the Pinus koraiensis seed dormancy release.