Physiological And Biochemical Changes Of Pomelo Fruit [Citrus Grandis(L.)Osbeck.cv.guanxi Miyou] In The Process Of Granulation During Maturity

The metabolisms of cell wall and free radical were studied on both hybridized Citrus guanxi-miyou fruit and its apomictic fruit in the process of granulation during maturity so that the reason and mechanism of granulation in juice sac could be probed. The changes in isoenzyme, titrable acid, and glucide of juice sac were also studied.1．Changes in cell wall hydrolases and their components of guanxi-miyou in the process of granulation during maturity were studied. The results showed that the activities of Carboxymethylcellulase (C_x), polygalacturonase(PG) and pectinesterase (PE) were closely associated with granulation.The activity of C_x in juice sac reached a peak value in middle stage of maturity and the activity of C_x in normal juice sac was higher than that of granulated juice sac, and the activity of C_x in apomictic fruits was lower than that of hybridized fruits. The activity of PE and PG in juice sac reached a peak value at the last stage of maturity synchronously and its in granulated sac was higher than that of normal juice sac.In the process of maturity, protopectin content kept decreasing, soluble pectin content in normal juice sac continued increasing, but soluble pectin of granulated juice sac reached a peak value then reduced tardily in the middle stage of maturity. The content of hemicellulose had no difference evidengly. The trend of cellulose in granulated juice sac was descending first, and then increasing .The cellulose content in normal juice sac tended to reducing. Whatever hybidized fruits or apomictic fruits, the cell wall material content, propectin content, cellulose content of granulated juice sac were more than that of normal juice sac,but the soluble pectin and water content of granulated juice sac were less than that of normal juice sac.2．The metabolism of free radical of pulp and juice sac in Citrus guanxi-miyou fruits in the process of granulation during maturity were studied. The results were as follows:Activities of POD and SOD appeared declining at the early and middle stage of maturity, and then rose sharply at the last stage similiarly. The activity of POD in granulated juice sac was higher than normal juice sac and that of in apomictic fruits was higher than hybridized fruits. The minimum activity of SOD in granulated sac appeared earlier than normal juice sac, and the minimum activity of SOD in apomictic fruits appeared earlier than that of hybridized fruits, the activity of apomictic fruits was weaker than that of hybridized fruits. The activity of CAT in granulated juice sac was higher than that of normal juice sac. GSH content of normal juice sac was more than that of granulated juice sac in the whole process of maturity. The content of MDA rose first, and then decreased last in juice sac in the process of maturity, the MDA content in granulated juice sac was more than that of normal juice sac.The activity of POD in pulp tended to declining sharply then kept stable ,that of in pulp of apomictic fruits was higher than that of hybridized fruits. The activity of SOD tended to descending at first and then to ascending in hybridized fruits. But it declined in apomictic fruits all along. The activity of SOD in pulp of hybridized fruits was higher than that of apomictic fruits. The activity of CAT reduced gradually. The Changes of CAT in pulp of hybridized fruits and apomictic fruits have no difference obviously. The contents of GSH, ASA and MDA in pulp of hybridized fruits were more than that of apomictic fruits respectively.3．Changes of isoenzymes in Citrus guanxi-miyou fruits were also studied. The results were as follows: POD isoenzyme and SOD isoenzyme had close relationship with granulation of juice sac. In apomictic fruits, POD isoenzyme had four enzyme strips in the whole stage of maturity, Rf₁=0．323, Rf₂=0．344, Rf₃=0．656, Rf₄=0．677,but it only had two strips in hybridized fruits. And all strips in granulated juice sac were higher than that of normal juice sac. SOD isoenzyme had six enzyme strips in sac of apomictic fruits. The strips of Rf₃ and Rf₄ in granulated juice sac were higher than that of normal juice sac especially, Strips of Rf₁ and Rf₆ were weaker until they cleared away in the process of matuirity. SOD isoenzyme had four strips in juice sac of hybridized fruits, all strips were weaker than that of apomictic fruits. CAT isoenzyme had three strips in sac of apomictic fruits, strips of CAT isoenzyme in granulated juice sac were stronger than normal juice sac, and they had no evident difference in the process of maturity. CAT isoenzyme strips were not found out in sac of hybridized fruits. 4．Trend of total soluble glucide, sucrose and fructose were similar in juice sac of Citrus guanxi-miyou fruits in the process of granulation during maturity, all of them appeared to be comulated sharply in the forepart and middle stage of maturity and then were stable at the last stage. The content of total soluble glucide in granulated juice sac was less than that of normal juice sac. The results showed that content of the total titrable acid in apomictic fruits was more than hybridized fruits, the content of the total titrable acid in normal juice sac were more than that of granulated juice sac,In the course of experiment, it was found that the hybridized fruits and apomictic fruits of Citrus guanxi-miyou had granulated in the process of maturity before harvest, the granulation index increased gradually as maturity degree deepened., and the appearance of granulation in apomictic fruits was earlier than hybridized fruits, and the granulated degree was more serious than that of the latter. In summary, it was thought that endogenous hormones made maturing degree of hybridized fruits hang behind apomictic fruits, delayed granulation of juice sac and reduced the extent. The cause of granulation could be concluded into two aspects: One was that weak activity of C_x brought about low speed of hydrolyzation on cellulose and hemicellulose. The other was that metabolism of free radical in granulated juice sac was active, which induced high activity of POD. The high activity of POD catalyzed H₂O₂ with hydroxybenzene material to form lignin, which made content of cellulose increasing, then the speed of hydrolyzation on cellulose was lower than speed of production. As a result, the cell wall was thicken and the guanulation occured in juice sac. At the same time, it was because that propectin was hydrolyzaed by high activity of PE to demonmethyl ester-pectin and then to soluble pectin by low activity of PG, but the production of PE was fixed by calcium bridge and esterifiable bone partly,led to gelation and depened the granulation of juice sac further.