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

Abstract

Many studies have shown that root-shoot imbalance influences vegetative growth and development of cotton (Gossypium hirsutum L.), but few have examined changes in leaf senescence and endogenous hormones due to stem girdling. The objective of this study was to determine the correlation between some endogenous phytohormones, particularly cytokinins and abscisic acid (ABA), and leaf senescence following stem girdling. Field-grown cotton plants were girdled on the main stem 5 days after squaring (DAS), while the non-girdled plants served as control. Plant biomass, seed cotton yield, main-stem leaf photosynthetic (Pn) rate, chlorophyll (Chl) and malondialdehyde (MDA) concentrations, as well as levels of cytokinins and ABA in main-stem leaves and xylem sap were determined after girdling or at harvest. Main-stem girdling decreased the dry root weight and root/shoot ratio from 5 to 70 days after girdling (DAG) and reduced seed cotton yield at harvest. Main-stem leaf Pn and Chl concentration in girdled plants were significantly lower than in control plants. Much higher levels of MDA were observed in main-stem leaves from 5 to 70 DAG, suggesting that stem girdling accelerated leaf senescence. Girdled plants contained less trans-zeatin and its riboside (t-Z ? t-ZR), dihydrozeatin and its riboside (DHZ ? DHZR), and isopentenyladenine and its riboside (iP ? iPA), but more ABA than control plants in both main-stem leaves and xylem sap. These results suggested that main-stem girdling accelerated leaf senescence due to reduced levels of cytokinin and/or increased ABA. Cytokinin and ABA are involved in leaf senescence following main-stem girdling.

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].…”

“…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. In the present study, we compared the difference between the transcriptomes of main-stem leaves obtained from an early senescence (K1) and a late senescence (K2) cotton using the Solexa sequencing system during leaf senescence.…”

“…As for cotton, senescence may occur too early or too late in the season due to environmental stresses or internal factors [3], [4]. Too early senescence of whole cotton plant is referred to as premature senescence, which has been occurring on an increasing scale since modern transgenic Bacillus thuringiensis Berliner (Bt) cotton ( Gossypium hirsutum L.) cultivars were introduced for commercial production [5], [6]. Wright [7], [8] indicated that premature senescence frequently developed during the period of rapid boll filling and this reduced lint yield and fiber quality, thus constituting an important constraint to cotton yield and quality.…”

Impact of girdling and leaf removal on Alhagi sparsifolia leaf senescence

“…So in our study, obstruction of mineral nutrients from roots to leaves may another reason for leaf senescence in girdled A. sparsifolia. In addition, stem girdling interrupts phloem transport of acropetal flow of cytokinin (Kong et al 2011), thus reduced levels of cytokinin which subsequently resulted in the acceleration of leaf senescence (Dai and Dong 2011). So induced senescence may also regulated by the change of phytohormones (e.g.…”

The Chlorophyll a Fluorescence Characteristic in Different Types of Leaf Senescence in Alhagi sparsifolia

“…Leaf senescence is induced by numerous factors, such as darkness (Buchanan-Wollaston and others 2005; Gregersen and others 2013), high light intensity (Fu and others 2012), high light dosage (Gregersen and others 2013;Noodén and others 1997), heat (Gregersen and others 2013;Lobell and others 2012), water stress (Yang and others 2003), nitrogen starvation (Koeslin-Findeklee and others 2014), salicylic acid (SA) (Vogelmann and others 2012), abscisic acid (ABA) (Gregersen and others 2013;Setter and others 1980), jasmonic acid (JA) (Jiang and others 2014), cytokinins (Zwack and others 2013), carbon famine (Brouquisse and others 2001;Parrott and others 2005), carbon feast (Moore and others 2003;Parrott and others 2005), and disease (Gregersen and others 2013;Robert-Seilaniantz and others 2011). Many experiments have shown that girdling can cause leaf carbohydrate accumulation and accelerate the senescence process (Krapp and Stitt 1995;Parrott and others 2007), girdling accumulates carbohydrates such as soluble sugar and starch, which cannot be expelled from source organs (leaf), which subsequently causes the accumulation of carbohydrates above the girdle (Dai and Dong 2011;Nebauer and others 2011;Rivas and others 2006;Roper and Williams 1989;Urban and Alphonsout 2007;Yang and others 2013) and results in the carbon feast-induced senescence in leaves (Parrott and others 2005;Parrott and others 2010;Parrott and others 2007).…”