The Development Of Paeonia Ostii Seeds And Oil Accumulation

Paeonia ostii is a woody oil crop that has attracted much attention in recent years,which has extremely high ornamental and economic value.The study of physiological and biochemical changes during the process of P.ostii seed oil accumulation plays a very important role in its industrialization.In this study,the proton density distribution of P.ostii seeds at different developmental stages was obtained by nuclear magnetic resonance imaging((MRI)).At the same time,the morphological development and oil body changes of P.ostii seeds were observed by stereomicroscope and transmission electron microscope(TEM).The contents of oleic acid,linoleic acid and α-linolenic acid during the development of P.ostii seeds were determined by gas chromatography-mass spectrometry(GC-MS).In addition,the biological characteristic indexes such as horizontal diameter,vertical diameter,fresh and dry weight of seeds and follicles at each developmental stage were measured.In order to further understand the law of oil accumulation and its metabolism and transformation with nutrients,the changes of the contents of soluble sugar,crude starch and soluble protein and the activities of nutrients and oil synthesis related enzymes in different developmental stages of P.ostii seeds were also studied.The main results are as follows:(1)The appearance color of follicles changed from green to yellowish brown during P.ostii follicles maturation,and finally appeared grayish brown after ripening and cracking.During the process of seed maturation,the seed coats color changed from yellow to white,and finally the seed coat was hard and dark brown.(2)At 45-95 days after flowering(DAF),the expansion period of follicles was basically synchronized with the development of seeds morphology,and the transverse and vertical diameter increased rapidly,and the transverse and vertical diameter decreased and tended to be stable after95 DAF.(3)Combined with stereoscopic microscope,it was observed that in the early stage of P.ostii seed development(45 DAF),there were mainly seed coat,outer integument and inner integument.At 45-85 DAF,with P.ostii seeds developing,the integument tissue degenerated continuously to provide nutrition for the formation of endosperm,and the area of endosperm increased continuously,this was an important period for seeds volumes to increase,and water should be provided in time.After 85 DAF,the integument degenerated completely,the endosperm reached the maximum area,and gradually hardened until the seeds were fully mature.At this stage,more attention should be paid to providing fertilizer for the growth of P.ostii plants.(4)Combined with MRI images,it can be observed that the P.ostii seeds development can be divided into two stages: morphological construction stage(45-85 DAF)and nutrition accumulation stage(95-115 DAF).At 45-85 DAF,there was an imbalance in the development rates of each follicle within the same follicles,and the development rates of the seeds in the same follicle were also different,and the development rates of seeds in the same follicle were basically the same until95 DAF.(5)TEM observation showed that compared with the oil bodies in the endosperm,the formation of oil bodies in the embryo was faster and earlier than that in the endosperm.With the continuous development of seeds,in embryo and endosperm,the area and number of vacuoles continue to decrease and disappear,and the high electron-dense substances continue to increase and gradually gather to form a larger mass structure,at the same time,the number and size of oil bodies continue to grow and spread from the cell wall to the center of the cell,and the sizes are staggered around the high electron-dense material.(6)The peak period of seed oil synthesis of P.ostii was mainly concentrated in 45-85 DAF,and the oil content increased continuously in the process of seed development,reaching 41.6% at the final maturity,while the water content decreased continuously in the process of development.there was a very significant negative correlation between oil content and water content.(7)The activity of ACCase and PPase in P.ostii seeds increased rapidly at 45-85 DAF,which was basically consistent with the peak period of oil synthesis.With the decrease of the rate of oil accumulation,the activity of ACCase and PPase decreased accordingly.(8)There was a significant positive correlation between soluble sugar content and crude starch content in each development stage of P.ostii seed.During the rapid seed expansion period(45-85 DAF),both of them provided nutrition for seed growth and development,and reached the lowest values of 33 mg/g FW and 11.7 mg/g FW respectively at 85 DAF.On the other hand,soluble protein accumulated rapidly at 45-85 DAF,corresponding to the consumption trend of sugars,and reached the highest value of 53.6 mg/g FW;at 85 DAF,which decreased slightly at 85-95 DAF,and then tended to be stable gradually.In addition,the changes of total amylase activity and total protease activity were consistent with the metabolic process of crude starch and soluble protein,respectively.(9)The three predominant unsaturated fatty acids accumulated simultaneously,and showed stages of initial accumulation(45-65 DAF)and rapid accumulation(65-105 DAF).The results suggested that the period 65-105 DAF was critical for unsaturated fatty acids accumulation in P.ostii seeds.(10)In the final stage of seed ripening(115 DAF),the oil content reached a high level,and the contents of water content,soluble protein,soluble sugar and crude starch were stable.Therefore,it is suitable for P.ostii seeds to be harvested about 115 DAF.