| Changes of photosynthesis, chlorophyll fluorescence, carbohydrate contents and activities of related enzymes of source leaves in response to source-sink manipulations by defruiting ('- fruit'), retaining fruit ('+ fruit') and removing bags covered leaves at different times on 1-year-old shoots and the limbs were studied during different phenological stages of fruit development in cv. 'Okubo', 'Yanfengyihao' and 'Bayuecui' peach trees (Prunus persica (L.) Batsch.). The following results were obtained:Fruit removal significantly decreased net photosynthesis rate (Pn), stomatal conductance (Gs) and transpiration rate (E), but significantly increased leaf temperature (TLeaf) at midday as compared with '+ fruit' in cv. 'Okubo' and 'Yanfengyihao' peach. Intercellular CO2 concentration (Ci) were not significantly affected by fruit removal.There were significant positive correlations between Pn and Gs at small stomatal apertures, and strong positive correlations between Pn and E. Moreover, Pn peaked when TLeaf was 38℃ ('Okubo' and 'Yanfengyihao') or 36℃ ('Bayuecui'), and then sharply decreased when TLeaf continued to increase in the presence or absence of fruit. However, Pn in '- fruit' was lower than that of'+ fruit' at the same TLeaf, especially when TLeaf exceeded 38℃ or 36℃. It is suggested that critical TLeaf may be 38℃ for cv. 'Okubo' and 'Yanfengyihao' and 36℃ for cv. 'Bayuecui'.Carboxylation efficiency (CE) of '- fruit' significantly lower than that of '+ fruit' under TLeaf exceeded 38℃ in 'Yanfengyihao', but no significant difference in CE was observed between '- fruit' and '+ fruit' under TLeaf less than 36℃ in 'Bayuecui'. Pn of'- fruit' significantly decreased may be associated with Ribulose bisphosphate (Rubisco) activity decreased when critical TLeaf exceeded a critical value.Fruit removal significantly decreased Pn, Fm, Fv/Fm, Fv/Fo, and increased TLeaf around midday, compared to '+ fruit' and removing bags treatments at different times in 'Bayuecui' peach. Electron transfer efficiency, photochemical efficiency, and potential activity of PS II decrease due to higher TLeaf were related to the observed decline in Pn after fruit removal in this study.Fruit removal significantly accumulated sorbitol and starch, but they didn't decrease activities of related enzymes in leaves. Opposition, activities of aldose-6-phosphate reductase (A6PR) and ADP-glucose pyrophosphorylase (ADPGPPase) in leaves of '- fruit' increased sometimes in cv. 'Yanfengyihao' peach. There were no correlations between accumulations of sorbitol and starch and photosynthesis decreased in leaves. Moreover, significant accumulation of sorbitol, sucrose and starch in source leaves of fruit removal, but no differences in photosynthesis between '- fruit' and '+ fruit' were observed in cv. 'Bayuecui'. It is suggested that the accumulation of end products in source leaves could not be the direct factor in regulating photosynthesis in peach trees.Contents of soluble sugars and starch in leaves regulated by related enzymes of carbohydrate metabolism or carbohydrate transportation from source to sink in day-night changes. Contents of sorbitol, sucrose and starch in leaves enhanced were regulated by activities of A6PR, SPS andADPGPPase increased respectively in the day. In the night, contents of sorbitol and sucrose in leaves decreased were associated with carbohydrate transportation decreased from source to sink, but contents of starch in leaves decreased were regulated by amylase activity increased. Sorbitol contents of'- fruit' in leaves higher than those of'+ fruit' because their A6PR activity higher than those of'+ fruit' in some times in the day. Contents of sucrose and starch of'- fruit' higher than those of'+ fruit' were observed mainly due to sucrose transportation decreased from source to sink and amylase activity decreased respectively in '- fruit' in the night.It is suggested that the decreased stomatal aperture and increased TLaf may be in regulating photosynthesis by Rubisco activity of PS II and phot...
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