关键词: 棉花, 蕾铃脱落, 果枝韧皮部阻断, 糖, 激素

Abstract:

【Objective】The abscission rate of squares and bolls is often more than 60%, and the sympodial leaves after squares and bolls shedding are often used as “auxiliary sources” to play an important role in the development of adjacent bolls. In order to enrich the “source-sink” regulation theory and provide theoretical basis for the regulation of cotton yield compensatory development, the activity changing characters of the “auxiliary sources” was explored after the shedding of their squares or bolls.【Method】In this study, two sowing dates (May 10 and June 1, 2021) of Zhongmian 425 were used to carry out a field experiment at the Pailou Experimental Station of Nanjing Agricultural University in Nanjing, Jiangsu province (118° 50′ E, 32° 02′ N). Under the conditions of fruiting branch phloem blocking, the changes of related indicators of leaf source capacity, such as cotton sympodial leaves morphological characteristics, gas exchange parameters, carbon and nitrogen substances and endogenous hormone content, were studied after defruiting (isolate the “source-sink” system on the first node at the fourth, fifth or sixth fruiting branches by chemical blocked the phloem, and then simulated the boll abscission condition by manual remove the bud or young bolls of the system).【Result】(1) The defruiting treatment significantly increased the content of fructose, sucrose, starch and cellulose in sympodial leaves, but significantly decreased the glucose content. With the extension of time, the increase of starch was the largest at 1 day after treatment (DAT), while that of cellulose was significantly larger at 3 DAT and that of sucrose, cellulose and starch was relatively larger at 5 DAT. (2) After treatment, carbohydrates accumulated more in the form of non-reducing sugars; photosynthates were more distributed to starch; polysaccharides/oligosaccharides decreased at first and then increased; while the C/N of sympodial leaves increased at first and then decreased. (3) The defruiting treatment significantly decreased the net photosynthetic rate and chlorophyll content of sympodial leaves. (4) The sympodial leaves showed purplish red locally, and compared with the control, the anthocyanin content increased by about 2 times. (5) After treatment, the content of ABA, JA, SA in sympodial leaves significantly increased compared with the control, and the content of IAA increased at first and then decreased, while the content of GA₃ was significantly lower than the control. (6) The dynamic balance of endogenous hormones in sympodial leaves changed after treatment: ABA/IAA and JA/IAA decreased at first and then increased, while ABA/GA₃ and JA/GA₃ increased continuously. 【Conclusion】After squares and bolls shedding, the forms of sugar accumulation and distribution as well as endogenous hormone signals in sympodial leaves changed significantly and had a significant effect on source capacity. In a short period of time (1-3 days), the overall content of sugars in sympodial leaves increased, especially the accumulation of non-reducing sugars, and the source capacity strengthen rapidly. However, with the passage of time, the enhancement of source capacity diminished, and the leaves had a tendency of senescence, while chlorophyll degradation accelerated. That was, after abscission, the “auxiliary source” function of the sympodial leaves increased rapidly in a short period of time (about 3 days), then decreased rapidly, and made limited contribution to the development of the adjacent bolls in the later stage.

Key words: cotton, squares and bolls shedding, phloem blocking, sugar, hormone