Field-grown Cotton Research Articles

Alternative electron sinks are crucial for conferring photoprotection in field-grown cotton under water deficit during flowering and boll setting stages.

To clarify the photoprotective mechanisms of cotton leaves under water deficit in the field, leaf gas exchange, chlorophyll a fluorescence as well as the corresponding physiological responses were examined in cotton (Gossypium hirsutum L.) to evaluate electron flux distribution. With increasing water deficit, net photosynthetic rate (Pn) significantly decreased, the total electron flux through PSII [Je(PSII)] gradually decreased and the fraction of electron flux required to sustain CO2 assimilation [Je(PCR)] markedly declined. Simultaneously, the ratio of quantum efficiency of PSII [Φ(PSII)] to the quantum efficiency of CO2 fixation [Φ(CO2)] increased, accompanied by an increase in the alternative electron flux (Ja). The enhanced alternative electron flux of O2-dependent Ja(O2-dependent) indicated that electrons had been transported to O2 in the Mehler-peroxide reaction (MPR) and that the remaining alternative electron flux Ja(O2-independent) had been used for nitrate reduction, as indicated by an increase in nitrate reductase (NR) and glutathinone reductase (GR) activities. In addition, mild water deficit increased the proportion of electron flux for the photorespiratory carbon oxidation [Je(PCO)]. Water deficit significantly increased surperoxide radical production rate (O2-•) and hydrogen peroxide content (H2O2), and the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD) and catalase (CAT) in cotton leaves also increased under water deficit. Therefore, the Mehler-peroxidation reaction, photorespiration and nitrate reduction helped to dissipated excess light energy, being important photoprotective mechanisms for adapting the photosynthetic apparatus to mild and moderate water deficit in cotton.

1-Methylcyclopropene and Aminoethoxyvinylglycine effects on yield components of field-grown cotton

Biotic and abiotic stresses can alter the hormone balance and trigger the activation of pathways involved in the cotton stress responses, resulting in the abscission of squares, flowers and young bolls and consequent reductions in the seed cotton yield and fiber yield. As part of the mechanism that primarily regulates the protective response of plants against stresses, ethylene is considered a key hormone involved in this response, and increased ethylene synthesis has been observed when plants are subjected to stress. Thus, the development of strategies aimed to mitigate their negative effects can reduce the shed rate of reproductive structures and positively impact cotton productivity. For this purpose, 1-methylcyclopropene (1-MCP), a compound that inhibits the action of ethylene, and aminoethoxyvinylglycine (AVG), an ethylene synthesis inhibitor, were sprayed on cotton plants to investigate their effects on the seed cotton yield (SCY), fiber yield (FY), fiber percentage (% Fiber) and final stand of plants (STAND) during two cotton growth seasons (2010 and 2011). To this end, experiments were performed in a randomized complete block design with five replicates. Our results demonstrate that the inhibitors of ethylene synthesis and action increased the seed cotton and fiber yield during both growing seasons. The results obtained after AVG spraying in the initial reproductive phase (first square emission) presented the highest values for the cotton yield components and are the first record of the success of this method in Brazil.

Lint yield and nitrogen use efficiency of field-grown cotton vary with soil salinity and nitrogen application rate

Understanding salinity and fertilizer interaction is of great economic importance to improving crop yield and fertilizer use efficiency. The objective of this study was to investigate the effects of nitrogen (N) rate on cotton yield and N use efficiency (NUE), and relate this to the optimum N fertilizer rate under saline field conditions. To achieve this goal, we conducted a two-year experiment in two nearby fields with similar fertility but varying salinity, using a split-plot design in the Yellow River Delta of China. The main plots were assigned to moderate (electrical conductivity of soil saturated paste extract, ECe=6.3dS/m) and high (ECe=12.5dS/m) salinity levels, while N-free (0kg/ha), low (120kg/ha), moderate (210kg/ha) and high (300kgN/ha) nitrogen rates were assigned to the subplots. The high-salinity soil produced 35% lower biological yield but 8.9% higher harvest index than the moderate-salinity soil. Biological yields were increased by 30% at low N rate, 35% at moderate N rate and 37% at high N rate. Under moderate salinity, moderate N rate produced more lint than other N rates; under the high salinity field, the low N rate produced lint yield comparable to the high- and moderate-N rates, being about 33% greater than that from 0-N rate. Moderate N rate was superior to high N rate but comparable to low rate based on agronomic NUE (aNUE), physiological NUE (pNUE), internal NUE (iNUE) and N recovery efficiency (NRE) under moderate salinity; under high salinity, the low N rate produced the greatest aNUE and NRE, and higher pNUE and iNUE than high N rate. Our overall results supported the use of moderate N rate for moderate salinity cotton fields and low N rate for high salinity fields in the saline Yellow River Delta and other cotton-growing areas with similar ecologies.

Leaf area relationships to plant vegetative characteristics in cotton (Gossypium hirsutum L.) grown in a temperate sub-humid environment

Measurement or estimation of leaf area is essential for understanding crop responses to experimental treatments. The objective of this study was to develop regression models for estimating leaf area of field-grown cotton (Gossypium hirsutum L.) from measurements of leaf dry weight (LDW), vegetative components (stems and leaves) dry weight (VDW) and plant height (PH). Three cotton cultivars (Deltapine 25, Sahel and Siokra 324) with different leaf morphologies were grown under varying growth conditions created by four different planting dates in a temperate sub-humid environment (Gorgan, Iran). Leaf area, LDW, VDW and PH were measured at one month after emergence, squaring, flowering, bolling, boll opening and second harvest. Data set for validation was collected during growing season of 2003 in different experiments. Measured leaf area ranged from 170 to 8167 cm 2 plant -1 . Different regression models were examined for describing leaf area relationships to LDW, VDW and PH. It was found that the power function gives the best fit in terms of R 2 and root mean square of error (RMSE). Cultivar differences were not significant and a general equation was adequate for all the three cultivars. LDW and VDW provided good estimation of leaf area. However, PH was not a good predictor of leaf area. It was concluded that cotton leaf area can be estimated or simulated as a function of LDW or VDW with reasonable accuracy.

Physiological and yield responses of field-grown cotton to application of urea with the urease inhibitor NBPT and the nitrification inhibitor DCD

Nitrogen deficiency and poor N use efficiency adversely affect cotton (Gossypium hirsutum L.) growth and yield. The objective of this study was to evaluate the performance of the urease inhibitor NBPT and the nitrification inhibitor DCD with urea fertilizer on the physiology and yield of irrigated cotton. Field experiments were conducted in 2009 and 2010 with the following treatments: untreated control, full recommended N rate with urea, 75% recommended N rate with urea, 75% recommended N rate with urea+NBPT, and 75% recommended N rate with urea+NBPT+DCD. The treatment Urea-75% plus NBPT improved cotton N uptake by 17% and N use efficiency by 41% when compared to the Urea-75% alone. NBPT addition to urea also positively affected leaf chlorophyll content, plant growth and fiber quality. The use of NBPT improved cotton lint yield by 14% compared to a similar urea application rate without NBPT. However, addition of DCD to urea fertilizer limited NBPT performance. The use of DCD resulted in decreased N uptake, N use efficiency, leaf chlorophyll, plant growth and yields. Under the field conditions of the current study, it is concluded that addition of NBPT to urea, but not DCD in combination with NBPT, improved N fertilization in cotton.

Decreased CO2 availability and inactivation of Rubisco limit photosynthesis in cotton plants under heat and drought stress in the field

Heat and drought stresses are often coincident and constitute major factors limiting global crop yields. A better understanding of plant responses to the combination of these stresses under production environments will facilitate efforts to improve yield and water use efficiencies in a climatically changing world. To evaluate photosynthetic performance under dry-hot conditions, four cotton (Gossypium barbadense L.) cultivars, Monseratt Sea Island (MS), Pima 32 (P32), Pima S-6 (S6) and Pima S-7 (S7), were studied under well-watered (WW) and water-limited (WL) conditions at a field site in central Arizona. Differences in canopy temperature and leaf relative water content under WL conditions indicated that, of the four cultivars, MS was the most drought-sensitive and S6 the most drought-tolerant. Net CO2 assimilation rates (A) and stomatal conductances (gs) decreased and leaf temperatures increased in WL compared to WW plants of all cultivars, but MS exhibited the greatest changes. The response of A to the intercellular CO2 concentration (A–Ci) showed that, along with stomatal closure, non-stomatal factors associated with heat stress also limited A under WL conditions, especially in MS. The activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) decreased in WL compared to WW plants, consistent with thermal inhibition of Rubisco activase activity. The extent of Rubisco deactivation could account for the metabolic limitation to photosynthesis in MS. Taken together, these data reveal the complex relationship between water availability and heat stress for field-grown cotton plants in a semi-arid environment. Both diffusive (drought-stress-induced) and biochemical (heat-stress-induced) limitations contributed to decreased photosynthetic performance under dry-hot conditions.

Nitrogen rate and plant density effects on yield and late-season leaf senescence of cotton raised on a saline field

Plant density and nitrogen fertilization are two important practices for field-grown cotton ( Gossypium hirsutum L.). The objective of this study was to investigate the effects of plant density and N fertilization rate, especially their interactions, on yield, yield components, late-season leaf senescence and Cry1Ac expression in Bt ( Bacillus thuringiensis) cotton under salinity conditions. To achieve this goal, we conducted a three-year experiment with a high-yielding Bt cotton cultivar (SCRC 28) in a moderately saline (ECe = 11 dS/m) field, using a split-plot design in the Yellow River Delta of China. The main plots were assigned to low, medium and high plant densities (3.0, 5.25 and 7.5 plants/m 2), while low, moderate and high nitrogen rates (120, 225 and 300 kg N/ha) were assigned to the subplots. Biological yield, lint yield, yield components, harvest index, boll load, Cry1Ac expression and leaf senescence were significantly affected by plant density and N rate. Lint yield was also affected by plant density × N rate interaction. Increased plant density or N rate enhanced biological yield, but reduced harvest index. Considerably high lint yield (1604 kg/ha) was achieved only with a high dose of N fertilizer under low plant density, but comparable yields (1693 and 1643 kg/ha) were achieved with moderate and low N rate under medium and high plant density. Increased plant density and N rate reduced boll load, which had highly significant negative correlation with late-season leaf photosynthesis ( r = −0.928) and significant correlation with Cry1Ac protein concentration ( r = −0.8131). Leaf senescence was delayed by increasing plant density and N rate mainly due to reduced boll load and a combination of reduced boll load and nutritional effect. Medium plant density with moderate N rate or high plant density with low N rate would enhance cotton yield and moderate Cry1Ac expression at reduced cost in the Yellow River Delta of China and other areas with similar ecologies.

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

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.

A screening strategy of fungal biocontrol agents towards Verticillium wilt of cotton

Three hundred and seventy-three fungal isolates were obtained from the endorhiza, rhizosphere, and bulk soil of field-grown cotton plants. One hundred and five of them produced obvious inhibition zones against Verticillium dahliae Kleb., so they were selected as antagonists towards this pathogen. An assessment system was established to evaluate these 105 antagonists for their biocontrol potential and plant growth-promoting potential. Their biocontrol potential was assessed according to their in vitro antagonistic activity against V. dahliae and activities of fungal cell wall degrading enzymes including protease, cellulase, and chitinase. Their plant growth-promoting potential was assessed according to their in vitro activities of solubilizing phosphate and fixing nitrogen. Thirty-three antagonists received at least three points of the total value of assessed biocontrol potential and plant growth-promoting potential and were tested for their biocontrol efficacy and growth-promoting effect on cotton under greenhouse conditions. Twelve of them achieved positive biocontrol efficacy ranging from 8.58% to 69.78%; the conventional correlation coefficient of the biocontrol efficacy of these antagonists with their assessed biocontrol potential was 0.926. By using the screening strategy developed in this study, Fusarium oxysporum strain By125, Nectria haematococca Bx247, and Phomopsis sp. By231 were identified as potential BCAs for controlling Verticillium wilt in cotton, for they achieved biocontrol efficacy of 63.63–69.78% towards this disease and increased biomass by 18.54–62.63% under greenhouse conditions. The present study also demonstrated that the endorhiza of field-grown cotton plants may be a richer source of potential BCAs against Verticillium wilt than the rhizosphere and bulk soil.

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

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.

Nutrient and hormone levels in cotton ovules during embryony

In vitro zygotic and somatic embryogenesis protocols rely on nutrient and hormone levels from media to satisfy the physiological and developmental requirements of embryony. To better understand these requirements for cotton, we quantified levels of major and minor elements, carbohydrates, NH4 +, free amino acids and six hormones in whole cotton ovules (with fibers removed), nucelli (ovules with integuments removed), or ovule fluid (extracted from the endosperm region). Samples were collected from field-grown cotton at 1–18 days-past-anthesis (DPA) during each of three growing seasons. Replication across 2 years was obtained for carbohydrates, NH4 +, free amino acids and hormones from nucellus samples. The year effect was large primarily for hormones only. The most abundant minerals across tissue types and years were K, P, Mg and S. Potassium was the most abundant at 260, 600 and 1,660 mmol kg−1 dry mass (DM) in nucelli, whole ovules and ovule fluid, respectively. Magnesium, Ca, Zn and Mn levels were 2–8-fold higher in ovule fluid compared to whole ovules or nucelli. In the free amino acid plus NH4 + category, NH4 +, alanine, serine, glycine, asparagine (plus aspartic acid), glutamine (plus glutamic acid), leucine, threonine and arginine predominated in nucelli and ovule fluid, and levels tended to be higher in the older samples across years and tissue types. Fructose and glucose levels also increased with age with very high levels being found in late DPA ovule fluid. Arabinose, inositol and melibiose were also prominent sugars. Indole-3-acetic acid levels were similar between nucelli and ovule fluid and ranged from 10 to 80 μmol kg−1 DM. An abscisic acid spike, from 15 to 400 μmol kg−1 DM, occurred in nucelli and whole ovules from 2 to 8 DPA. Thereafter, abscisic acid levels remained between 5 and 10 μmol kg−1 DM. Zeatin and zeatin riboside were the most abundant cytokinins, and levels of these hormones fluctuated between 1 and 4 μmol kg−1 DM in both nucelli and ovule fluid.

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

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 trans-zeatin 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.

Expression of genes associated with carbohydrate metabolism in cotton stems and roots.

BackgroundCotton (Gossypium hirsutum L) is an important crop worldwide that provides fiber for the textile industry. Cotton is a perennial plant that stores starch in stems and roots to provide carbohydrates for growth in subsequent seasons. Domesticated cotton makes these reserves available to developing seeds which impacts seed yield. The goals of these analyses were to identify genes and physiological pathways that establish cotton stems and roots as physiological sinks and investigate the role these pathways play in cotton development during seed set.ResultsAnalysis of field-grown cotton plants indicated that starch levels peaked about the time of first anthesis and then declined similar to reports in greenhouse-grown cotton plants. Starch accumulated along the length of the stem and the shape and size of the starch grains from stems were easily distinguished from transient starch. Microarray analyses compared gene expression in tissues containing low levels of starch with tissues rapidly accumulating starch. Statistical analysis of differentially expressed genes indicated increased expression among genes associated with starch synthesis, starch degradation, hexose metabolism, raffinose synthesis and trehalose synthesis. The anticipated changes in these sugars were largely confirmed by measuring soluble sugars in selected tissues.ConclusionIn domesticated cotton starch stored prior to flowering was available to support seed production. Starch accumulation observed in young field-grown plants was not observed in greenhouse grown plants. A suite of genes associated with starch biosynthesis was identified. The pathway for starch utilization after flowering was associated with an increase in expression of a glucan water dikinase gene as has been implicated in utilization of transient starch. Changes in raffinose levels and levels of expression of genes controlling trehalose and raffinose biosynthesis were also observed in vegetative cotton tissues as plants age.

Individual and combined effects of salinity and waterlogging on Cry1Ac expression and insecticidal efficacy of Bt cotton

Salinity, waterlogging and a combination of both stresses are severe threats to plant growth, development and yield of field-grown cotton ( Gossypium hirsutum L.), but their individual or combined effects on insecticidal efficacy of Bacillus thuringiensis (Bt) transgenic cotton and the underlying mechanisms are not well understood. In the present study, two cotton cultivars (33B and SCRC17) containing the Cry1Ac insecticidal protein gene were planted in 10 L pots filled with soil and allowed to grow in a greenhouse. The potted plants were either treated with NaCl (5 mg/g, w/w), waterlogging, or a combination of both stresses at the three true-leaf stage, and levels of total soluble protein, Bt insecticidal protein, gossypol and the control efficacy as indicated by mortality of bollworm larvae were examined at 7-day intervals after stress. Waterlogging and a combination of salinity and waterlogging reduced total protein content by 40–46% and 45–65% and Bt protein content by 38–50% and 45–72% from 7 to 21 days after stress, relative to the non-stressed control, respectively. The control efficacy was significantly reduced by either waterlogging or the combined stress. Regression analysis indicated that Bt protein content was correlated to total soluble protein content ( R 2 = 0.7677*), while Bt cotton efficacy was correlated to Bt protein level ( R 2 = 0.7917**). Salinity reduced Bt protein by 11–22% and total soluble protein by 5.7–7.2% from 7 to 21 days after NaCl stress, but did not result in reduction in control efficacy. It is concluded that reduced bollworm control efficacy under waterlogging or the combined stress could be mainly attributed to the declined levels of Bt protein, which is closely associated with the inhibited nitrogen metabolism by stresses. As one of the secondary compounds that are toxic to pests, increases in gossypol may be involved in maintaining the efficacy when Bt protein level was reduced under salinity.

DEVELOPING ACCURATE SPATIAL MAPS OF COTTON FIBER QUALITY PARAMETERS

Awareness of the importance of cotton fiber quality (Gossypium, L. sps.) has increased as advances in spinning technology require better quality cotton fiber. Recent advances in geospatial information sciences allow an improved ability to study the extent and causes of spatial variability in fiber parameters. However, these studies are often harvested by hand and ginned on small research gins. Fiber quality from cotton lint harvested and ginned in this manner is different from that machine-harvested and ginned on production-scale equipment. The objective of this study was to develop a method of correcting for error introduced into cotton fiber quality parameters from samples as a result of harvest and ginning methods. This correction method will allow more realistic comparisons between results that researchers commonly report and measurements that a producer would receive. Field-grown cotton was harvested either by machine or hand, and ginned on a small research gin or a production-scale gin. The results reported here examine the population characteristics for physiological fiber parameters including micronaire, strength, length and uniformity. The correction needed for translating the research results to the production scale was determined. The error inherent in that correction was determined for different populations of cotton fibers from different years. To demonstrate the impact of the research-induced error and the correction factor, spatial maps of cotton fiber length are plotted.

Does N or K Nutrition Affect Bronze Wilt in Field-Grown Cotton?

Bronze wilt (BW) is a disorder of cotton (Gossypium hirsutum L.) that has reduced yields of susceptible cultivars, and may recur in future cultivar releases. Because BW may impair uptake or translocation of mineral nutrients, soil fertility may affect BW incidence or its impact on growth and development. A 3-year study was conducted to determine effects of N and K fertility and tillage on BW incidence and impact on growth and development of field-grown cotton. Incidence of BW was relatively low and unaffected by N or K fertility in this study with or without tillage. Neither N fertility nor tillage affected growth and development responses to BW, although high N fertility delayed appearance of secondary symptoms by an average of 3.5 days. Plant growth response to K fertility was suppressed by BW. Boll retention was reduced more than vegetative growth by BW, but this response was not mitigated by N or K fertilization. Leaves of BW plants had equivalent K concentration as normal plants, but 30% lower P, indicating that BW impaired P uptake or translocation. Results suggest that N and K fertilization are not useful methods to manage BW, but P nutrition merits further research. Accepted for publication 17 August 2008. Published 17 November 2008.

Circumvention of Over‐Excitation of PSII by Maintaining Electron Transport Rate in Leaves of Four Cotton Genotypes Developed under Long‐Term Drought

We investigated the patterns of response to a long-term drought in the field in cotton cultivars (genotypes) with known differences in their drought tolerance. Four cotton genotypes with varying physiological and morphological traits, suited to different cropping conditions, were grown in the field and subjected to a long-term moderate drought. In general, cotton leaves developed under drought had significantly higher area-based leaf nitrogen content (N (area)) than those under well irrigation. Droughted plants showed a lower light-saturated net photosynthetic rate (A (sat)) with lower stomatal conductance (g (s)) and intercellular CO (2) concentration (C (i)) than irrigated ones. Based on the responses of A (sat) to g (s) and C (i), there was no decreasing trend in A (sat) at a given g (s) and C (i) in droughted leaves, suggesting that the decline in A (sat) in field-grown cotton plants under a long-term drought can be attributed mainly to stomatal closure, but not to nonstomatal limitations. There was little evidence of an increase in thermal energy dissipation as indicated by the lack of a decrease in the photochemical efficiency of open PSII (F (v)'/F (m)') in droughted plants. On the basis of electron transport (ETR) and photochemical quenching (q (P)), however, we found evidence indicating that droughted cotton plants can circumvent the risk of excessive excitation energy in photosystem (PS) II by maintaining higher electron transport rates associated with higher N (area), even while photosynthetic rates were reduced by stomatal closure.

Response of Cotton to Potassium Fertilizer on Effectiveness of Fruiting Sites in Aridisols

A field experiment was conducted to assess the effectiveness of fruiting positions along sympodia under varying levels and sources of potassium (K) fertilizer on field-grown cotton in an arid environment. Treatments consisted of four rates of K (0, 62.5, 125.0, 250.0 kg K ha− 1) and two types of K (K2SO4 and KCl). Cotton cultivar S-12 (Gossypium hirsutum L.) was used as a test crop. Plant mapping data showed that the total number of fruiting positions, number of intact fruit on sympodia/monopodia, and percent of bolls per position on sympodia differed greatly under different doses of K fertilizer. The percentage of fruit retention was markedly improved under increasing doses of K fertilizer as compared with the K-unfertilized treatment. The percent survival of harvestable bolls for the first five positions along sympodia at the end of the season was 30%, 25%, 18%, 13%, and 8%, respectively. Potassium fertilization stimulated cotton crop in lengthening sympodial branches and retaining more fruit on the first three positions and also at the bottom of the plant during the early reproductive phase. The fruiting pattern was 2–3 and 6–7 d vertical and horizontal fruiting interval, respectively.

Field-grown cotton plants with elevated activity of chloroplastic glutathione reductase exhibit no significant alteration of diurnal or seasonal patterns of excitation energy partitioning and CO 2 fixation

Transgenic cotton plants with elevated activity of chloroplast-targeted glutathione reductase (GR+) were grown in field plots over two seasons in order to compare their photosynthetic performance with that of wildtype plants. We hypothesised that transgenic plants would show enhanced protection of the photosynthetic apparatus against photoinhibition, primarily through an increase in electron transport associated with the role of the chloroplastic antioxidant system as an alternative electron sink. Diurnal measurements of chlorophyll a fluorescence from cotyledons, stem leaves, and leaves subtending developing fruits (bolls) were used to estimate the rate of linear electron transport ( J e) and the rates of reversible, regulated (NPD REG) and photoinhibitory (NPD PI) non-photochemical energy dissipation (NPD) at several times (June, July, September, October) during each growing season. GR+ cotyledons exhibited greater J e than wildtype cotyledons during the middle of a day in early June, while NPD PI was the same for both genotypes. Throughout most days on which measurements were conducted, no genotypic differences in J e and NPD were observed for stem leaves. Only during the late morning of one day in early October did leaves subtending bolls of GR+ plants exhibit greater J e compared to that for wildtype plants. As leaves subtending bolls of both genotypes aged, J e and CO 2 assimilation declined, while NPD increased. Maximum NPD PI and minimum F v/ F m remained essentially the same for all measurement days. However, the maximum NPD REG, the greatest contributor to NPD, increased with leaf age. We conclude that the rapid rise in leaf temperature during most mornings created conditions in which elevated GR activity conferred no advantage. Also, as light energy absorption became excessive in late morning, cotton leaves exhibited a strong capacity for regulated, non-photochemical energy dissipation that may have served as the major photoprotective mechanism.

Seasonal Patterns of Glutathione and Ascorbate Metabolism in Field-Grown Cotton under Water Stress

The goal of this study was to identify water-stress-related limitations in the antioxidant protection in cotton (Gossypium hirsutum L.) in the field. Cotton was grown under full irrigation and severe-to-moderate water deficits in both years of the study. The amount and form of glutathione (5-L-glutamyl-L-cysteinylglycine) were monitored in both years, while the antioxidant enzymes ascorbate peroxidase and glutathione reductase, the amount of ascorbate, and the amount of malondialdehyde (MDA) were monitored in the second year of the study. The amount of glutathione varied (> 2x) during the sampling interval, though there was no effect of water treatment on the variation. The ratio of reduced/oxidized glutathione varied seasonally, but not in response to water deficits. Gluthione reductase activity varied ( 5×) seasonally, but again not in response to water deficits. The amount of ascorbate and the activity of ascorbate peroxidase were increased under water stress ( 5 × and 1.5×, respectively). The amount of MDA (an indicator of oxidative damage) varied seasonally ( 2×), though not in response to water stress. While glutathione metabolism appears sufficient for oxidative stresses resulting from field-water deficits, altered ascorbate metabolism may be a response to water deficits in the field. Malondialdehyde amount did not increase with water stress, suggesting that antioxidant metabolism was sufficient for the oxidative stresses. It is apparent that antioxidant metabolism in these plants exposed to water deficits under production conditions was sufficient to protect against oxidative damage.