A Study On Cellular And Molecular Biology Of Plastid Development In Peach Fruit

The plastid is the most conspicuous organelle found in eukaryotic cells.Fruit plastids play a key role in development of fruit.In this paper,in order to study the changes in physiology,cytobiology and molecular level during the plastid development in peach flesh,the white-fleshed ‘Jiucui',yellow-fleshed ‘23-40' and red-fleshed ‘B15-48' peach with shading treatment were explored by using spectrophotometry,Imaging-PAM,frozen section methods,electron microscopy,Western blot,immunohistochemistry and real-time fluorescence quantitative PCR.The main results showed as follows.1.In natural illumination,with development of fruit the contents of chlorophyll decreased and the contents of anthocyanin increased.The contents of carotenoid in 'Jiucui' decreased gradually,but increased in ‘23-40' and ‘B15-48'.In mature stage,the contents of carotenoid in ‘23-40' and anthocyanin in ‘B15-48' were the highest in the different color flesh fruits.Shading treatment constrained the accumulation of chlorophyll,carotenoid and anthocyanin during peach fruit development.But it had no effects on the contents of carotenoid in ‘23-40' and anthocyanin in ‘B15-48' in mature fruits.2.Photosynthetic activity of the peach mesocarp showed spatio-temporal heterogeneity.3.The morphology and distribution of chloroplasts in peach flesh also had temporal and spatial differences.The amount of chloroplasts in peach flesh decreased gradually from outside to inside.And with the development of fruits,the amount of chloroplasts declined,and the volume of chloroplast became smaller.At last chloroplasts disappeared during maturity.In addition,plastids in ‘Jiucui' and ‘B15-48' became colorless after chloroplasts degradation.Chloroplasts in '23-40' were transformed from green to yellow,and eventually transformed into yellow chromoplasts.4.During ripen stage,the changes were generally followed by chloroplasts to globular chromoplasts differentiation which involved the appearance of abundant plastoglobuli and rich peripheral reticulum with the disintegration of thylakoid in the ligh.Shading treatment restrained the plastoglobuli generation of ‘Jiucui' and ‘B15-48'.But it brought about the appearance of chromoplast in ‘23-40' and peripheral reticulum in ‘B15-48' at the earlier stage.5.The expression level of photosynthetic proteins of LSU,psbO,D1,Lhcb1 and Cyt b559 in peach flesh was lower than that in leaf tissue.With fruit development,their expression level decreased.The spatio-temporal heterogeneity on expression of these proteins in the flesh was consistent with the chloroplasts distribution and the changes of chlorophyll fluorescence.6.The ptDNA copy number per cell in peach flesh increased with the fruits development.