Weijiang Li

Effects of cotton rootstock on endogenous cytokinins and abscisic acid in xylem sap and leaves in relation to leaf senescence

Leaf senescence varies greatly among cotton cultivars, possibly due to their root characteristics, particularly the root-sourced cytokinins and abscisic acid (ABA). Early-senescence (K1) and late-senescence (K2) lines, were reciprocally or self-grafted to examine the effects of rootstock on leaf senescence and endogenous hormones in both leaves and xylem sap. The results indicate that the graft of K1 scion onto K2 rootstock (K1/K2) alleviated leaf senescence with enhanced photosynthetic (Pn) rate, increased levels of chlorophyll (Chl) and total soluble protein (TSP), concurrently with reduced malondialdehyde (MDA) contents in the fourth leaf on the main-stem. The graft of K2 scion onto K1 rootstock enhanced leaf senescence with reduced Pn, Chl, and TSP, and increased MDA, compared with their respective self-grafted control plants (K1/K1 and K2/K2). Reciprocally grafted plants differed significantly from their self-grafted control plants in levels of zeatin and its riboside (Z+ZR), isopentenyl and its adenine (iP+iPA), and ABA, but not in those of dihydrozeatin and its riboside (DHZ+DHZR) in leaves in late season, which was consistent with variations in leaf senescence between reciprocally and self-grafted plants. The results suggest that leaf senescence is closely associated with reduced accumulation of Z+ZR, and iP+iPA rather than DHZ+DHZR, or enhanced ABA in leaves of cotton. Genotypic variation in leaf senescence may result from the difference in root characteristics, particularly in Z+ZR, iP+iPA, and ABA which are regulated by the root system directly or indirectly.

Effects of non-uniform root zone salinity on water use, Na+ recirculation, and Na+ and H+ flux in cotton

A new split-root system was established through grafting to study cotton response to non-uniform salinity. Each root half was treated with either uniform (100/100 mM) or non-uniform NaCl concentrations (0/200 and 50/150 mM). In contrast to uniform control, non-uniform salinity treatment improved plant growth and water use, with more water absorbed from the non- and low salinity side. Non-uniform treatments decreased Na+ concentrations in leaves. The [Na+] in the ‘0’ side roots of the 0/200 treatment was significantly higher than that in either side of the 0/0 control, but greatly decreased when the ‘0’ side phloem was girdled, suggesting that the increased [Na+] in the ‘0’ side roots was possibly due to transportation of foliar Na+ to roots through phloem. Plants under non-uniform salinity extruded more Na+ from the root than those under uniform salinity. Root Na+ efflux in the low salinity side was greatly enhanced by the higher salinity side. NaCl-induced Na+ efflux and H+ influx were inhibited by amiloride and sodium orthovanadate, suggesting that root Na+ extrusion was probably due to active Na+/H+ antiport across the plasma membrane. Improved plant growth under non-uniform salinity was thus attributed to increased water use, reduced leaf Na+ concentration, transport of excessive foliar Na+ to the low salinity side, and enhanced Na+ efflux from the low salinity root.

Differential expression of induced resistance by an aqueous extract of killed Penicillium chrysogenum against Verticillium wilt of cotton

Dry mycelium of Penicillium chrysogenum (PEN), a waste product of the pharmaceutical industry, was extracted with water and applied to the roots of two Gossypium hirsutum cultivars (H552 and Vered) and two G. barbadense cultivars (PF15 and P906) to examine its efficacy in controlling Verticillium dahliae Kleb. Soil application of 5% PEN provided significant protection against Verticillium wilt in all the tested cultivars, although PF15 and P906 were genetically more resistant to the wilt disease than H552 and Vered. As PEN did not inhibit mycelial growth of V. dahliae in vitro, it is inferred that the disease controllingeffects of PEN are attributed to induced resistance. Percentage protection induced by PEN in H552 and Vered was significantly higher than that of PF15 and P906, and the older seedlings of H552 showed a relatively higher percentage of protection than younger seedlings of the same cultivar, suggesting that the expression of induced resistance was somewhat cultivar-dependent and seedling age-dependent. Treatment with 5% PEN increased peroxidase (POX) activity and lignin deposition in hypocotyls at 16–48 and 24–48 h after PEN treatment, respectively. We assume that POX might result in lignification and thus be associated with the defense against Verticillium wilt. It is concluded that dry mycelium of PEN may be used to induce resistance against V. dahliae in cotton. r 2002 Elsevier Science Ltd. All rights reserved.

Gene expression profiles deciphering leaf senescence variation between early- and late-senescence cotton lines.

Leaf senescence varies greatly among genotypes of cotton (Gossypium hirsutium L), possibly due to the different expression of senescence-related genes. To determine genes involved in leaf senescence, we performed genome-wide transcriptional profiling of the main-stem leaves of an early- (K1) and a late-senescence (K2) cotton line at 110 day after planting (DAP) using the Solexa technology. The profiling analysis indicated that 1132 genes were up-regulated and 455 genes down-regulated in K1 compared with K2 at 110 DAP. The Solexa data were highly consistent with, and thus were validated by those from real-time quantitative PCR (RT-PCR). Most of the genes related to photosynthesis, anabolism of carbohydrates and other biomolecules were down-regulated, but those for catabolism of proteins, nucleic acids, lipids and nutrient recycling were mostly up-regulated in K1 compared with K2. Fifty-one differently expressed hormone-related genes were identified, of which 5 ethylene, 3 brassinosteroid (BR), 5 JA, 18 auxin, 8 GA and 1 ABA related genes were up-regulated in K1 compared with K2, indicating that these hormone-related genes might play crucial roles in early senescence of K1 leaves. Many differently expressed transcription factor (TF) genes were identified and 11 NAC and 8 WRKY TF genes were up-regulated in K1 compared with K2, suggesting that TF genes, especially NAC and WRKY genes were involved in early senescence of K1 leaves. Genotypic variation in leaf senescence was attributed to differently expressed genes, particularly hormone-related and TF genes.

H2O2 and ABA signaling are responsible for the increased Na+ efflux and water uptake in Gossypium hirsutum L. roots in the non-saline side under non-uniform root zone salinity

Non-uniform root salinity increases the Na(+)efflux, water use, and growth of the root in non-saline side, which may be regulated by some form of signaling induced by the high-salinity side. However, the signaling and its specific function have remained unknown. Using a split-root system to simulate a non-uniform root zone salinity in Gossypium hirsutum L., we showed that the up-regulated expression of sodium efflux-related genes (SOS1, SOS2, PMA1, and PMA2) and water uptake-related genes (PIP1 and PIP2) was possibly involved in the elevated Na(+) efflux and water use in the the roots in the non-saline side. The increased level of indole acetic acid (IAA) in the non-saline side was the likely cause of the increased root growth. Also, the abscisic acid (ABA) and H2O2 contents in roots in the non-saline side increased, possibly due to the increased expression of their key biosynthesis genes, NCED and RBOHC, and the decreased expression of ABA catabolic CYP707A genes. Exogenous ABA added to the non-saline side induced H2O2 generation by up-regulating the RBOHC gene, but this was decreased by exogenous fluridone. Exogenous H2O2 added to the non-saline side reduced the ABA content by down-regulating NCED genes, which can be induced by diphenylene iodonium (DPI) treatment in the non-saline side, suggesting a feedback mechanism between ABA and H2O2.Both exogenous ABA and H2O2 enhanced the expression of SOS1, PIP1;7 ,PIP2;2, and PIP2;10 genes, but these were down-regulated by fluridone and DPI, suggesting that H2O2 and ABA are important signals for increasing root Na(+) efflux and water uptake in the roots in the non-saline side.

Fruiting-branch removal enhances endotoxin expression and lint yield in Bt cotton

Abstract A two-year field experiment was conducted to determine the effects of removal of early-fruiting branches (REFB) on yield, quality, and endotoxin expression in transgenic Bt (Bacillus thuringiensis) cotton (Gossypium hirsutum L.). Two early-fruiting branches of field-grown cotton plants were removed and retained at squaring to form the REFB and the control treatments, respectively. Lint yield, yield components, fibre quality, and Cry1Ac protein concentration in the first fully expanded young leaves on the main stem were measured. Results show that lint yields were increased by 5.1 and 5.5% with REFB compared with control in 2004 and 2005, respectively. There was no difference in fibre quality in the first two harvests between REFB and control, but fibre strength and micronarie in the third harvest were improved with REFB. Levels of total N, soluble protein, and Cry1Ac protein as well as glutamic-pyruvic transaminase (GPT) activity in leaves were higher in REFB than in the control. Laboratory bioassay showed significant enhancement of the control efficacy by REFB in terms of Helicoverpa armigera (Hübner) neonate mortality for both years. It is suggested that REFB might be a potential practice for enhancing transgenic Bt cotton production.

Non-uniform salinity in the root zone alleviates salt damage by increasing sodium, water and nutrient transport genes expression in cotton.

Non-uniform salinity alleviates salt damage through sets of physiological adjustments in Na+ transport in leaf and water and nutrient uptake in the non-saline root side. However, little is known of how non-uniform salinity induces these adjustments. In this study, RNA sequencing (RNA-Seq) analysis shown that the expression of sodium transport and photosynthesis related genes in the non-uniform treatment were higher than that in the uniform treatment, which may be the reason for the increased photosynthetic (Pn) rate and decreased Na+ content in leaves of the non-uniform salinity treatment. Most of the water and nutrient transport related genes were up-regulated in the non-saline root side but down-regulated in roots of the high-saline side, which might be the key reason for the increased water and nutrient uptake in the non-saline root side. Furthermore, the expression pattern of most differentially expressed transcription factor and hormone related genes in the non-saline root side was similar to that in the high-saline side. The alleviated salt damage by non-uniform salinity was probably attributed to the increased expression of salt tolerance related genes in the leaf and that of water and nutrient uptake genes in the non-saline root side.

Global gene expression in cotton (Gossypium hirsutum L.) leaves to waterlogging stress.

Cotton is sensitive to waterlogging stress, which usually results in stunted growth and yield loss. To date, the molecular mechanisms underlying the responses to waterlogging in cotton remain elusive. Cotton was grown in a rain-shelter and subjected to 0 (control)-, 10-, 15- and 20-d waterlogging at flowering stage. The fourth-leaves on the main-stem from the top were sampled and immediately frozen in liquid nitrogen for physiological measurement. Global gene transcription in the leaves of 15-d waterlogged plants was analyzed by RNA-Seq. Seven hundred and ninety four genes were up-regulated and 1018 genes were down-regulated in waterlogged cotton leaves compared with non-waterlogged control. The differentially expressed genes were mainly related to photosynthesis, nitrogen metabolism, starch and sucrose metabolism, glycolysis and plant hormone signal transduction. KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis indicated that most genes related to flavonoid biosynthesis, oxidative phosphorylation, amino acid metabolism and biosynthesis as well as circadian rhythm pathways were differently expressed. Waterlogging increased the expression of anaerobic fermentation related genes, such as alcohol dehydrogenase (ADH), but decreased the leaf chlorophyll concentration and photosynthesis by down-regulating the expression of photosynthesis related genes. Many genes related to plant hormones and transcription factors were differently expressed under waterlogging stress. Most of the ethylene related genes and ethylene-responsive factor-type transcription factors were up-regulated under water-logging stress, suggesting that ethylene may play key roles in the survival of cotton under waterlogging stress.

Soaking in H2O2 regulates ABA biosynthesis and GA catabolism in germinating cotton seeds under salt stress

Exogenous H2O2 improves seed germination with the involvement of ABA and GA in a number of plant species but how it affects cotton seed germination under salinity stress is not well documented. In this study, we found that the marked inhibition of cotton seed germination under salinity stress was considerably alleviated by pretreatment with H2O2. Salt stress increased the ABA content by upregulating ABA biosynthesis genes, NCED2, NCED5 and NCED9 and downregulating the ABA catabolism gene, CYP707A2. It also decreased the GA content by increasing the expression of GA catabolism gene, GA2ox1 and decreasing that of the GA biosynthesis gene, GA20ox1 during germination. Pretreatment with H2O2 downregulated the ABA biosynthesis genes, NCED5 and NCED9, thereby decreasing the ABA content in germinating seeds. Concurrently, it increased the GA content by downregulating the GA catabolism gene, GA2ox1. These results suggest that pretreatment with H2O2 improved cotton seed germination by mediating the downregulation of ABA catabolism and GA biosynthesis under salt stress.