Hezhong Dong

Increased glycine betaine synthesis and salinity tolerance in AhCMO transgenic cotton lines

Glycine betaine is an osmoprotectant that plays an important role and accumulates rapidly in many plants during salinity or drought stress. Choline monooxygenase (CMO) is a major catalyst in the synthesis of glycine betaine. In our previous study, a CMO gene (AhCMO) cloned from Atriplex hortensis was introduced into cotton (Gossypium hirsutum L.) via Agrobacterium mediation to enhance resistance to salinity stress. However, there is little or no knowledge of the salinity tolerance of the transgenic plants, particularly under saline-field conditions. In the present study, two transgenic AhCMO cotton lines of the T3 generation were used to study the AhCMO gene expression, and to determine their salinity tolerance in both greenhouse and field under salinity stress. Molecular analysis confirmed that the transgenic plants expressed the AhCMO gene. Greenhouse study showed that on average, seedlings of the transgenic lines accumulated 26 and 131% more glycine betaine than those of non-transgenic plants (SM3) under normal and salt-stress (150xa0mmolxa0l−1 NaCl) conditions, respectively. The osmotic potential, electrolyte leakage and malondialdehyde (MDA) accumulation were significantly lower in leaves of the transgenic lines than in those of SM3 after salt stress. The net photosynthesis rate and Fv/Fm in transgenic cotton leaves were less affected by salinity than in non-transgenic cotton leaves. Therefore, transgenic cotton over-expressing AhCMO was more tolerant to salt stress due to elevated accumulation of glycine betaine, which provided greater protection of the cell membrane and photosynthetic capacity than in non-transgenic cotton. The seed cotton yield of the transgenic plants was lower under normal conditions, but was significantly higher than that of non-transgenic plants under salt-stressed field conditions. The results indicate that over-expression of AhCMO in cotton enhanced salt stress tolerance, which is of great value in cotton production in the saline fields.

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.

Exogenous nitric oxide delays salt-induced leaf senescence in cotton (Gossypium hirsutum L.)

Nitric oxide (NO) is a signaling molecule which plays an important role in delaying leaf senescence and increasing abiotic stress tolerance, but it is not clear if and how exogenous NO delays salt-induced leaf senescence in cotton. In this study, uniform cotton seedlings with five true main-stem leaves were cultured in hydroponics for 20xa0days and subjected to 150xa0mM NaCl. Seedlings were then treated with foliar spray of 300xa0μM sodium nitroprusside (SNP), a nitric oxide donor, and those with water spray were used as control. The effects of SNP on leaf senescence and expression of senescence-related genes were examined. Foliar spray with SNP significantly delayed leaf senescence in terms of the increased chlorophyll (Chl) content, photosynthetic (Pn) rate and expression of LHCB gene at 22xa0days after salt stress (DAS). The SNP significantly (pxa0<xa00.05) increased the expression of SOS1 and NHX1 genes and K+ content in leaves, but decreased leaf Na+ content. It also reduced (pxa0<xa00.05) the expression of ABA biosynthesis genes, NCED2, NCED9, and ABA content but increased the expression of cytokinin biosynthesis gene, IPT1 and ZR and iPA contents at 22xa0DAS. The overall results suggest that the delay in salt-induced leaf senescence by SNP was due to marked decrease in Na+ and ABA contents and increase in K+ and cytokinin through regulation of the expression of SOS1, NHX1, NCED2, NCED9 and IPT1 genes under salt stress. Foliar spray with SNP can be potentially useful in delaying leaf senescence, thereby increasing the economic yield of cotton under salt stress.

Yield, Leaf Senescence, and Cry1Ac Expression in Response to Removal of Early Fruiting Branches in Transgenic Bt Cotton

Two-year field experiments were conducted at Linqing, Yellow River valley of China, to study the plant response to the removal of early fruiting branches in transgenic Bt (Bacillus thuringiensis) cotton (Gossypium hirsutum L.) from 2003 to 2004. Plants were undamaged and treated by removing two basal fruiting branches (FB) at squaring to form the control and the removal treatment, respectively. The plant height, leaf area (LA), dry weight of fruiting forms (DWFF), the number of fruiting nodes (NFN), photosynthetic (Pn) rate, and levels of leaf chlorophyll (Chl), N, P, K, and Cry1Ac protein in main- stem leaves were measured at a 10- or 20-d interval after FB removal, and the sink/source ratio as indicated by NFN1LA and DWFFILA was determined. FB removal significantly increased the plant height, LA, and plant biomass in both years. Lint yields were increased 7.5 and 5.2% by removal compared with their controls in 2003 and 2004, respectively. Significant increases in boll size (5.7 and 5.1%) were also observed in removal than in control for both years. Either NFN/LA or DWFF/LA was significantly reduced by removal before 40 d after removal; however, both NFN/LA and DWFF/LA were significantly enhanced by FB removal at 80 d after removal compared to the untreated control. There was no significant difference in fiber quality in the first two harvests between removal and control, but fiber strength and micronarie in the third harvest were significantly improved by FB removal. In terms of leaf Chl, Pn rate, levels of total N, P, and K in late season, leaf senescence was considerably delayed by FB removal. Levels of Cry1Ac protein in the fully expanded young leaves were considerably higher in FB-excised plants than in control, indicating FB removal enhanced Cry1Ac expression. It is suggested that the yield and quality improvement with FB removal may be attributed to the increased NFN/LA or DWFF/LA in late season and delayed leaf senescence, respectively. FB removal can be a potential practice incorporated into the intensive cultivation system for enhancing transgenic Bt cotton production.

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.

Effects of N, P, and K Fertilizer Application on Cotton Growing in Saline Soil in Yellow River Delta

Abstract This study aimed at guiding fertilizer management for Bt cotton cultivar SCRC28 growing in coastal saline soil in the Yellow River Delta area in Shandong Province, China. SCRC28 was planted in the soils with high, middle, and low salinity under 3 fertilizer treatments, namely control (no fertilizers), NPK, NP, and NK. The effects of different fertilization treatments on nutrient assimilation, Na + assimilation, net photosynthetic rate ( P n ), dry matter accumulation, and lint yield of Bt cotton were investigated. Compared to the corresponding controls, the NP and NPK treatments had significantly higher nutrient uptake levels in plants in the 3 types of saline soils, and significantly lower levels of Na + uptake, especially the NPK treatment. The nutrient use efficiencies in agronomy of cotton in the NPK treatment were the highest among treatments regardless the salinity level. The N use efficiencies in agronomy were 0.20, 1.95, and 2.07 kg lint kg −1 under the low, middle, and high salinity level, respectively; the P use efficiencies in agronomy were 0.87, 8.35, and 8.71 kg lint kg −1 , respectively; and the K use efficiencies in agronomy were 0.26, 2.89, and 3.77 kg lint kg −1 , respectively. The NPK treatment also maintained the highest levels of leaf area, chlorophyll content, and P n among fertilization treatments in the 3 types of saline soils. The NPK treatment obtained the highest biomass and lint yield among the treatments, and the link yields were enhanced, compared to the corresponding controls, by 2.53%, 28.67%, and 30.47% in the low, middle, and high salinity soils, respectively. The effect of fertilization was obviously in the middle or high salinity fields. In this study, the fertilization quantities were based on the salinity level of soil. The NPK treatments were applied with N 165 kg ha −1 plus P 2 O 5 38.57 kg ha −1 plus K 2 O 111.5 kg ha −1 in the middle salinity soil and N 135 kg ha −1 plus P 2 O 5 32.14 kg ha −1 plus K 2 O 74.35 kg ha −1 in the high salinity soil. Therefore, rational fertilization schemes are recommended according to the salinity level of soil in order to alleviate nutrition obstacles and improve cotton nutrition, which ultimately result in the increases of nutrient use efficiencies in agronomy and cotton yield.

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.