Effects of early-fruit removal on endogenous cytokinins and abscisic acid in relation to leaf senescence in cotton

Abstract

Numerous studies have shown that early-fruit removal enhances vegetative growth and development of cotton (Gossypium hirsutum L.). However, few studies have examined changes in leaf senescence and endogenous hormones due to fruit removal. The objective of this study was to determine the correlation between some endogenous phytohormones, particularly the cytokinins and abscisic acid (ABA), and leaf senescence following fruit removal. Cotton was grown in pots and in the field during 2005 and 2006. Two early-fruiting branches were excised from plants at squaring to form the fruit removal treatment while the non-excised plants served as control. Plant biomass, seed cotton yield, cytokinins and ABA levels in main-stem leaves and xylem sap as well as main-stem leaf photosynthetic rate (Pn) and chlorophyll (Chl) concentration were determined after removal or at harvest. Fruit removals increased the leaf area, root and shoot dry weight and plant biomass at 35 days after removal (DAR), whether in potted or field-grown cotton; under field conditions, it also improved plant biomass and seed cotton yield at harvest. The Pn and Chl concentration in excised plants were significantly higher than in control plants from 5 to 35 DAR, suggesting that fruit removal considerably delayed leaf senescence. Fruit-excised plants contained more transzeatin and its riboside (t-Z ? t-ZR), dihydrozeatin and its riboside (DHZ ? DHZR), and isopentenyladenine and its riboside (iP ? iPA) but less ABA in both main-stem leaves and xylem sap than control plants from 5 to 35 DAR. These results suggest that removal of early fruiting branches delays main-stem leaf senescence, which can be attributed to increased cytokinin and/or reduced ABA. Cytokinin and ABA are involved in leaf senescence following early fruit removal.

Manipulation of dry matter accumulation and partitioning with plant density in relation to yield stability of cotton under intensive management

“…The reduced boll size of the third harvest should also be due to the relatively lower cotton yield at the extremely low plant density (1.5 plants m −2 ). These results were consistent with previous reports that adjusting sink/source ratios and optimizing population density can effectively delay leaf senescence and increase seedcotton yield (Dong et al, 2005(Dong et al, , 2006b(Dong et al, , 2009). …”

Gene Expression Profiles Deciphering Leaf Senescence Variation between Early- and Late-Senescence Cotton Lines

“…Leaf cytokinin content was increased in fruit-removal plants but decreased in girdled plants; in contrast, the ABA content was decreased in fruit removal plants and increased in girdled plants [6], [52]. Our previous results also suggested that the cotton line, K1 senescence earlier than K2 due to its lower cytokinin and higher ABA contents [19], [52].…”

“…Leaf cytokinin content was increased in fruit-removal plants but decreased in girdled plants; in contrast, the ABA content was decreased in fruit removal plants and increased in girdled plants [6], [52]. Our previous results also suggested that the cotton line, K1 senescence earlier than K2 due to its lower cytokinin and higher ABA contents [19], [52]. Although studies have indicated possible correlation of leaf senescence with cytokinins and ABA in cotton [6], [19], [52], the expression profiles of senescence-related genes, particularly hormone related and TF genes and their involvement in senescence regulation in cotton have not been documented.…”

Stem girdling influences concentrations of endogenous cytokinins and abscisic acid in relation to leaf senescence in cotton

“…Water-deficit stress accelerated leaf senescence through more accumulation of ABA in plant leaves (Pic et al 2002). Although previous studies have reported possible correlation of leaf senescence with cytokinins and ABA in cotton (Dong et al 2008(Dong et al , 2009, their contribution to leaf senescence and plant integrity after stem girdling has not been studied.…”