Cotton Photosynthesis Research Articles

Growth, leaf anatomy, and photosynthesis of cotton (Gossypium hirsutum L.) seedlings in response to four light-emitting diodes and high pressure sodium lamp

BackgroundLight is a critical factor in plant growth and development, particularly in controlled environments. Light-emitting diodes (LEDs) have become a reliable alternative to conventional high pressure sodium (HSP) lamps because they are more efficient and versatile in light sources. In contrast to well-known specialized LED light spectra for vegetables, the appropriate LED lights for crops such as cotton remain unknown.ResultsIn this growth chamber study, we selected and compared four LED lights with varying percentages (26.44%–68.68%) of red light (R, 600–700 nm), combined with other lights, for their effects on growth, leaf anatomy, and photosynthesis of cotton seedlings, using HSP lamp as a control. The total photosynthetic photon flux density (PPFD) was (215 ± 2) μmol·m−2·s−1 for all LEDs and HSP lamp. The results showed significant differences in all tested parameters among lights, and the percentage of far red (FR, 701–780 nm) within the range of 3.03%–11.86% was positively correlated with plant growth (characterized by leaf number and area, plant height, stem diameter, and total biomass), palisade layer thickness, photosynthesis rate (Pn), and stomatal conductance (Gs). The ratio of R/FR (4.445–11.497) negatively influenced the growth of cotton seedlings, and blue light (B) suppressed stem elongation but increased palisade cell length, chlorophyll content, and Pn.ConclusionThe LED 2 was superior to other LED lights and HSP lamp. It had the highest ratio of FR within the total PPFD (11.86%) and the lowest ratio of R/FR (4.445). LED 2 may therefore be used to replace HPS lamp under controlled environments for the study of cotton at the seedling stage.

Optimal row spacing configuration to improve cotton yield or quality is regulated by plant density and irrigation rate

ContextConventional high-density planting of machine-picked cotton in Xinjiang is associated with poor light distribution and low fiber quality. The objective of this study was to assess how different row spacing configurations, irrigation rates, and planting densities impact cotton photosynthetic production and fiber quality. MethodsWe conducted a 3-year field experiment in Shihezi, Xinjiang, China, to evaluate the impact of different row spacing configurations and irrigation amounts on cotton photosynthesis and fiber quality. The four row spacing configurations used were: RS66+10H (high-density with 66 +10 cm spacing), RS66+10L (low-density with 66 +10 cm spacing), RS76H (high-density with 76 cm spacing), and RS76L (low-density with 76 cm spacing). Additionally, two irrigation amounts were tested: MD-T3 (mulch drip irrigation with three tapes on one film) and MD-T2 (mulch drip irrigation with two tapes on one film). We measured and compared the distribution of cotton canopy leaves, light, canopy apparent photosynthesis, reproductive organs and fiber quality among these groups. ResultsThe results showed that RS66+10H had a higher lint yield than RS76L under MD-T2, with an increase of 5.4–7.1%. This can be attributed to the higher fraction of photosynthetically active radiation, canopy apparent photosynthesis (CAP), and boll biomass in RS66+10H between the full boll and boll opening stages. The maximum lint yield (3227–3580 kg ha−1) was obtained in RS66+10H under MD-T3. Interestingly, RS76L had a similar lint yield to RS66+10H under MD-T3, mainly due to the middle and lower canopy having higher leaf area index (LAI) values ranging from 1.8 to 2.1. This resulted in increased CAP and cotton boll biomass of the middle and lower canopy compared to RS66+10H during the full boll to boll opening stage. Under MD-T3, RS76L also exhibited longer fiber length in the middle and lower canopy (30.2–32.0 mm and 31.6–33.3 mm, respectively) compared to RS66+10H, with a difference of 3.2–3.8% and 5.6–6.5%. Furthermore, RS76L demonstrated higher fiber strength in the middle and lower canopy (31.4–32.7 cN tex−1 and 33.2–33.9 cN tex−1, respectively) compared to RS66+10H, with a difference of 2.6–6.2% and 5.9–6.8%. Maintaining an LAI of around 2.0 during the transition from full boll to boll opening stage optimized canopy architecture and enhanced photosynthetic productivity. ConclusionUnder adequate irrigation, RS76L could be a suitable replacement for RS66+10H in order to improve cotton fiber quality by optimizing leaf-boll spatial distribution. This study provides guidance for selecting the appropriate row spacing configuration under different water conditions. RS66+10H is recommended for increasing yield under water-deficient conditions, while RS76L is suitable for improving fiber quality under adequate irrigation.

GhCYS2 governs the tolerance against cadmium stress by regulating cell viability and photosynthesis in cotton

Cysteine, an early sulfur-containing compound in plants, is of significant importance in sulfur metabolism. CYS encodes cysteine synthetase that further catalyzes cysteine synthesis. In this investigation, CYS genes, identified from genome-wide analysis of Gossypium hirsutum bioinformatically, led to the discovery of GhCYS2 as the pivotal gene responsible for Cd2+ response. The silencing of GhCYS2 through virus-induced gene silencing (VIGS) rendered plants highly susceptible to Cd2+ stress. Silencing GhCYS2 in plants resulted in diminished levels of cysteine and glutathione while leading to the accumulation of MDA and ROS within cells, thereby impeding the regular process of photosynthesis. Consequently, the stomatal aperture of leaves decreased, epidermal cells underwent distortion and deformation, intercellular connections are dramatically disrupted, and fissures manifested between cells. Ultimately, these detrimental effected culminating in plant wilting and a substantial reduction in biomass. The association established between Cd2+ and cysteine in this investigation offered a valuable reference point for further inquiry into the functional and regulatory mechanisms of cysteine synthesis genes.

Novel Insights into the Contribution of Cyclic Electron Flow to Cotton Bracts in Response to High Light.

Cyclic electron flow around photosystem I (CEF-PSI) is shown to be an important protective mechanism to photosynthesis in cotton leaves. However, it is still unclear how CEF-PSI is regulated in non-foliar green photosynthetic tissues such as bracts. In order to learn more about the regulatory function of photoprotection in bracts, we investigated the CEF-PSI attributes in Yunnan 1 cotton genotypes (Gossypium bar-badense L.) between leaves and bracts. Our findings demonstrated that cotton bracts possessed PROTON GRADIENT REGULATION5 (PGR5)-mediated and the choroplastic NAD(P)H dehydrogenase (NDH)-mediated CEF-PSI by the same mechanism as leaves, albeit at a lower rate than in leaves. The ATP synthase activity of bracts was also lower, while the proton gradient across thylakoid membrane (ΔpH), rate of synthesis of zeaxanthin, and heat dissipation were higher than those of the leaves. These results imply that cotton leaves under high light conditions primarily depend on CEF to activate ATP synthase and optimize ATP/NADPH. In contrast, bracts mainly protect photosynthesis by establishing a ΔpH through CEF to stimulate the heat dissipation process.

Responses of cotton photosynthesis and growth to a new irrigation control method under deficit irrigation

Derived from an agricultural system model, a new cost-effective and water-saving decision support system for irrigation scheduling (DSSIS) was developed to control field irrigation of cotton ( Gossypium hirsutum L .) at the Qira oasis, Xinjiang, China. DSSIS used the water stress factor and soil water content simulated by the Root Zone Water Quality Model (RZWQM2) to trigger irrigation and to calculate the irrigation amount. In this study, its potential effects on cotton photosynthesis and development were evaluated in field experiments (2017, 2018). Arranged in a randomized complete design with four replicates, the experiment contained three irrigation control methods [DSSIS–based (DSS), soil moisture sensor–based (SMS), and conventional experience–based (CE)] and two irrigation rates [full and deficit irrigation (75% of full irrigation)]. Based on the two–year results, the DSS significantly improved both leaf photosynthesis and root biomass. Compared to the SMS, the DSS and CE significantly enhanced net leaf photosynthetic rate ( Pn ) by 20.1% and 19.5%, respectively, stomatal conductance ( Gs ) by 38.9% and 36.5%, respectively, and transpiration rate ( Tr ) by 19.5% and 17.1%, respectively. The DSS and CE outperformed the SMS by producing higher aboveground and root biomass, plant height, leaf area, and weight and number of marketable bolls per plant ( p ≤ 0.05). Compared to full irrigation, deficit irrigation caused 11.2%, 18.7%, and 10% decline in Pn, Gs, and Tr , respectively, but did not negatively affect fruiting branches or individual boll weight. The DSS demonstrated its capacity to maintain leaf photosynthesis and growth of cotton under arid conditions with better water use efficiency. • Cotton photosynthesis was evaluated under a new irrigation control method. • Leaf photosynthesis and root biomass significantly improved under DSS. • Deficit irrigation significantly decreased leaf photosynthesis. • The DSS didn’t affected cotton growth and development under arid conditions.

Examining effects of salt stress on leaf photosynthesis of cotton based on the FvCB model

To understand the responsive mechanism of leaf photosynthesis of cotton to salinity stress, we investigated the effects of salt stress on leaf photosynthetic characteristics of cotton seedlings with the FvCB model under five levels of salt concentration, i.e., 0 (CK), 50, 100, 150 and 200 mmol·L-1. Results showed that, compared with CK, the salt concentrations of 50 and 100 mmol·L-1 increased the maximum carboxylation rate (Vc max) and the maximum electron transport rate (Jmax), while the salt concentrations of 150 and 200 mmol·L-1 significantly decreased Vc max and Jmax. The net photosynthetic rate (Pn), mesophyll conductance (gm) and dark respiration rate (Rd) gradually decreased with the increases of salt concentration. Compared with CK, the salt concentrations of 50 and 100 mmol·L-1 did not affect gm, but significantly decreased Pn and Rd. The salt concentrations of 150 and 200 mmol·L-1 significantly decreased Pn, gm and Rd, which were significantly different from the salt concentrations of 0, 50 and 100 mmol·L-1. Pn of cotton seedlings under different salt concentrations was simulated by the FvCB model. Compared with the results from the FvCB model without considering gm, the FvCB model with gm improved the determination coefficient between the simulated and measured values and decreased the mean absolute error. The salinity threshold of cotton seedlings ranged between 100 and 150 mmol·L-1. With the increases of salt concentration, the limiting factor of leaf photosynthesis changed from mesophyll conductance to impaired components of photosynthetic apparatus. The FvCB model combined gm could improve the accuracy of photosynthesis simulation.

Study on the effects of polymer modifiers and phloem girdling on cotton in cadmium-contaminated soil in Xinjiang Province, China

The effects of two liquid modifiers (polyacrylate compound modifier and organic polymer compound modifier) and phloem girdling (stem girdling and branch girdling) on cadmium (Cd) content, Cd transport, and photosynthetic parameters of cotton (Xinluzao 60) in Cd-contaminated soil (40 mg kg −1) were studied through barrel experiment. The results showed that the distribution ratios of Cd in stem, leaves, and bolls, leaf net photosynthetic rate (Pn), leaf stomatal conductance (Gs), leaf transpiration rate (Tr), and chlorophyll content were decreased after girdling; and the application of modifiers reduced the Cd content and the Cd transported to the shoot, while alleviating photosynthetic damage caused by girdling. In general, our results indicated that the inhibition of carbohydrate supply caused by girdling reduced the photosynthetic capacity of cotton, while the applications of the two liquid modifiers decrease the influence to cotton photosynthesis. Moreover, Cd and modifiers may be transported to the shoot through both phloem and xylem.

Photochemical reflectance index and solar-induced fluorescence for assessing cotton photosynthesis under water-deficit stress

Rapid and non-destructive assessment of water status is essential to enhance crop performance. This study aimed to evaluate photosynthetic performance and to monitor water status in cotton under field conditions. A two-year experiment was conducted with three irrigation regimes to measure the following parameters: photochemical reflectance index (PRI), structural independent pigment index (SIPI), water index (WI), solar-induced fluorescence (SIF; retrieved from reflectance by using Fraunhofer line-depth method), gas exchange, and chlorophyll fluorescence (CF). The results showed that PRI decreased > 30 % in moderate drought (MD) and >50 % in severe drought (SD), compared with control. PRI was found to be positively correlated with net photosynthetic rate (PN), stomatal conductance, transpiration rate, actual quantum yield of photosystem II photochemistry (ΦPSII), but a negatively correlated with nonphotochemical quenching (NPQ). Solar-induced fluorescence around 761 nm (SIF761) had significant correlations with PN, ΦPSII, and NPQ, but not with maximal quantum yield of PS II photochemistry (Fv/Fm). The relationship between PRI and PN was stronger at the beginning of water stress (R2 = 0.86) than for the all stress stages (R2 = 0.54), indicating that PRI could be more effective for assessing PN of cotton at early water stress. PRI was better correlated with relative water content and photosynthetic parameters than SIPI and WI and so it could also be a good indicator to evaluate cotton water status.

Short-term effects of surface dust: alleviating photoinhibition of cotton under high irradiance in the Tarim Basin

Dust deposition on leaf surfaces can impact the growth and physiological traits of plants. We carried out a field experiment to investigate short-term effects of light surface dust on photosynthesis of cotton in the Tarim Basin using chlorophyll fluorescence and gas-exchange techniques. JIP-test analysis of OJIP curves showed that the total performance index for leaves without dust decreased by 32% at noon compared to the morning value. High irradiance at noon reduced actual quantum yield of PSII and increased nonphotochemical quenching for leaves without dust, showing photoinhibition. It suggested that light surface dust alleviated photoinhibition of cotton to high irradiance on a short-term basis. For the leaves without dust, high irradiance induced photoinhibition not only with respect to the photochemistry reactions but the biochemical pathways of CO2 fixation. Mechanisms such as thermal dissipation and enhanced electron flux to PSI protected the photosynthetic apparatus under high irradiance.

Photosynthesis and biomass allocation of cotton as affected by deep-layer water and fertilizer application depth

Available water stored in deep soil layers could increase the photosynthetic capacity of cotton. It was hypothesized that the photosynthesis of cotton would be enhanced by changing the fertilizer application depth under different deep-layer water conditions. We examined two deep-layer water levels, i.e., well-watered (W80) and not watered (W0), combined with surface application (F10) and deep application (F30) of basal fertilizer. Compared to W0, W80 resulted in increased leaf area (LA), photosynthetic pigment contents, maximal PSII efficiency (Fv/Fm), effective quantum yield of PSII (YII) and PSI (YI), electron transport rate of PSII (ETRII) and PSI (ETRI). W80 also increased the aboveground and root dry mass by 39 and 0.6%, respectively, and decreased the root/shoot ratio by 40–73%. Under the W0 condition, higher values of Fv/Fm, YII, YI, ETRII, and ETRI were measured for F10 compared to F30 after 69 d from emergence. Under the W80 condition, cotton plants with F10 showed higher LA, Fv/Fm, YII, YI, ETRII, and ETRI, but there were no significant differences in the photosynthetic pigments compared to F30. Our results suggest that sufficient water in deeper soil layers and the surface application of basal fertilizer could increase photosynthetic activity and efficiency, which promoted aboveground dry mass accumulation and partitioning towards reproductive organs.

Combined application of polymer coated potassium chloride and urea improved fertilizer use efficiencies, yield and leaf photosynthesis of cotton on saline soil

Conventional potassium fertilizers had been used widely, but few studies paid attention to controlled-release potassium fertilizer. The objective of this study was to explore the effects of polymer coated potassium chloride (PCPC) -an innovation product, especially the interaction application of PCPC and polymer coated urea (PCU) on cotton yield, fiber quality, leaf photosynthesis and fertilizer use efficiencies under salinity stressed conditions. A two-year experiment was conducted in two nearby fields with the similar fertility but varying salinity, using a split-plot design in the Yellow River Delta area of China. The main plots were assigned to the types of K fertilizers (K1-180kgha-1K from potassium sulfate, K2-90kgha-1K from potassium sulfate+90kgha-1K from PCPC, K3-54kgha-1K from potassium sulfate+126kgha-1K from PCPC, hereafter referred to as 0, 50% and 70% PCPC), while the types of N fertilizers (N1-220kgha-1N from urea, N2-110kgha-1N from urea+110kgha-1N from PCU, N3-66kgha−1N from urea+154kgha-1N from PCU, hereafter referred to as 0, 50% and 70% PCU) were assigned to the subplots. The results indicated that the lint yield, number of bolls, boll weight, lint percentage, fiber qualities, leaf photosynthesis and fertilizer use efficiencies were significantly affected by the types of K, N fertilizers and their interaction. The K and N release characteristics of PCPC and PCU under field condition were closely matched to the nutrients requirements of cotton growth. The contents of soil available K and inorganic N were significantly augmented from the first bloom stage to the initial boll-opening stage by using PCPC and PCU compared to potassium sulfate and urea treatments. Meanwhile, PCPC and PCU interaction increased lint yields by 11.16–26.44% and 14.17–32.11% in comparison with potassium sulfate and urea in 2014 and 2015, respectively, and the maximum lint yield was achieved by the combination of 70% PCPC and 50% PCU. Besides, the boll number and boll weight were improved 5.2–18.2% and 4.75–10.29% by the PCPC and PCU treatments compared to both potassium sulfate and urea treatments, respectively. The potassium recovery efficiency (KRE) and nitrogen recovery efficiency (NRE) of PCPC and PCU treatments were significantly raised by 24.34–33.77% and 19.68–36.25%, respectively, compared with potassium sulfate and urea treatments in 2014 and 2015. PCPC owned the great potential to alter the current application of potassium fertilizer due to its ubiquitous traits. The interaction of PCPC and PCU at optimal dose was significant on cotton growth in saline soil. Consequently, the application of 70% PCPC in combination with 50% PCU is recommended to increase cotton yield and fertilizer use efficiency, and to improve the fiber quality and leaf photosynthesis properties in the Yellow River Delta area of China.

Palmer Amaranth (Amaranthus palmeri) Competition for Water in Cotton

Palmer amaranth is a troublesome weed in cotton production. Yield losses of 65% have been reported from season-long Palmer amaranth competition with cotton. To determine whether water is a factor in this system, experiments were conduced in 2011, 2012, and 2013 in Citra, FL, and in Tifton, GA. In 2011, infrequent rainfall lead to drought stress. The presence of Palmer amaranth resulted in decreased soil relative water content up to 1 m in depth. Cotton stomatal conductance (gs) was reduced up to 1.8 m from a Palmer amaranth plant. In 2012 and 2013 higher than average rainfall resulted in excess water throughout the growing season. In this situation, no differences were found in soil relative water content or cottongsas a function of proximity to Palmer amaranth. A positive linear trend was found in cotton photosynthesis and yield; each parameter increased as distance from Palmer amaranth increased. Even in these well-watered conditions, daily water use of Palmer amaranth was considerably higher than that of cotton, at 1.2 and 0.49 g H20 cm−2d−1, respectively. Although Palmer amaranth removed more water from the soil profile, rainfall was adequate to replenish the profile in 2 of the 3 yr of this study. However, yield loss due to Palmer amaranth was still observed despite no change ings, indicating other factors, such as competition for light or response to neighboring plants during development, are driving yield loss.

Ethylene Inhibitors Increase Net Assimilation Rate and Cotton Boll Dry Matter Under Drought

Although the ethylene inhibitors role on reduction rate of boll abscission in cotton plants submitted to drought is being recently reported, its effects on photosynthesis performance and on cotton boll dry matter across the sympodial branch is scarce. Thus, the objective of this study was to evaluate the cotton photosynthesis and its boll dry matter performance across the reproductive branches via positional mapping in plants sprayed with ethylene inhibitors and submitted to water deficit. 1-methylcyclopropene (1-MCP), an inhibitor of ethylene action and aminoethoxyvinylglycine (AVG), an inhibitor of its synthesis, were sprayed on cotton plants alone and in association. Treatments were composed by (T1) control, where deionized water was sprayed; (T2) sprayed with AVG at 0.15 g a.i. L-1; (T3) 1-MCP at 0.076 g a.i. L-1; (T4) AVG at 0.15 g a.i. L-1 plus 1-MCP at 0.076 g a.i. L-1; (T5) AVG at 0.15 g a.i. L-1 twice at each seven days; (T6) 1-MCP sprayed at 0.076 g a.i. L-1 twice using the same interval and (T7) AVG at 0.15 g a.i. L-1 plus 1-MCP at 0.076 g a.i. L-1 twice at each seven days. The ethylene inhibitors sustained higher photosynthesis performance and higher boll dry mass across reproductive branches independent of compound, its combination or entries number. Highlight that a AVG (T2) or its 1-MCP association in two entries (T7) showed the best performance for dry matter accumulation, especially in the two first reproductive branches, while they maintained the highest photosynthesis rates at the end of stress period.

Nitrogen and Light Responses of Cotton Photosynthesis and Implications for Crop Growth

Leaf nitrogen content and light intensity affect leaf photosynthesis. Responses of cotton (Gossypium hirsutum L.) leaf photosynthesis to nitrogen and light were developed and used in a framework that scales from leaf photosynthesis to canopy radiation use efficiency (RUE). This was then used to explore the impact of nitrogen and light dynamics on RUE of cotton canopies. Photosynthetic rate and nitrogen concentration of leaves (specific leaf nitrogen, SLN) were measured from two field experiments in which the rate of nitrogen application was varied. The overall shape of the relationship between photosynthesis and SLN of individual leaves was consistent with that for other species, being described by an exponential rise to a maximum of 32.49 ± 1.08 μmol CO2 m−2 s−1 Incorporating the influence of age improved the relationship, showing an impact of leaf age independent of SLN. The photosynthesis relationship developed should be appropriate for use in simulating cotton crops. The approach used to scale from leaf photosynthesis to canopy RUE was effective in capturing the variation in the RUE of cotton as observed in three field experiments. There appeared to be little impact of the ontogenetic changes in light extinction coefficient and vertical gradients of SLN within the canopy on the variation in RUE. For crop simulation purposes, this simplifies the process of modulating RUE in growth models.

Nitrogen and Light Responses of Cotton Photosynthesis and Implications for Crop Growth

Leaf nitrogen content and light intensity affect leaf photosynthesis. Responses of cotton (Gossypium hirsutum L.) leaf photosynthesis to nitrogen and light were developed and used in a framework that scales from leaf photosynthesis to canopy radiation use efficiency (RUE). This was then used to explore the impact of nitrogen and light dynamics on RUE of cotton canopies. Photosynthetic rate and nitrogen concentration of leaves (specific leaf nitrogen, SLN) were measured from two field experiments in which the rate of nitrogen application was varied. The overall shape of the relationship between photosynthesis and SLN of individual leaves was consistent with that for other species, being described by an exponential rise to a maximum of 32.49 ± 1.08 μmol CO2 m−2 s−1 Incorporating the influence of age improved the relationship, showing an impact of leaf age independent of SLN. The photosynthesis relationship developed should be appropriate for use in simulating cotton crops. The approach used to scale from leaf photosynthesis to canopy RUE was effective in capturing the variation in the RUE of cotton as observed in three field experiments. There appeared to be little impact of the ontogenetic changes in light extinction coefficient and vertical gradients of SLN within the canopy on the variation in RUE. For crop simulation purposes, this simplifies the process of modulating RUE in growth models.

Protecting cotton photosynthesis during moderate chilling at high light intensity by increasing chloroplastic antioxidant enzyme activity.

This study examined the effect of increasing chloroplastic superoxide dismutase (SOD), ascorbate peroxidase (APX), or glutathione reductase (GR) activity via plant transformation of cotton on the initial recovery of photosynthesis following exposures to 10 degrees C and high photon flux density (PFD). Growing wild-type or non-expressing segregate plants (controls) and transformants at two PFDs (600 micromol m(-2) s(-1) and full sun) resulted in a range of total antioxidant enzyme activities. Total SOD activities above that for control leaves grown in full sun did not substantially improve the recoveries of CO(2)-saturated photosynthesis, especially for stress treatments lasting more than 1 h, while elevated APX or GR activity did improve recoveries after 1-3 h of the chilling treatment. No synergistic effects were noted when the activities of more than one antioxidant enzyme were elevated in transgenic hybrids. Although these results suggest that the protection of photosynthesis can be realized by reducing either superoxide or H(2)O(2) levels, thereby reducing the possibility of hydroxyl radical formation, the situation is complicated, since elevated APX or GR activity can improve recoveries even when additional SOD activity has no effect. In conclusion, to enhance the protection of photosynthesis using stroma-targeted antioxidant enzymes, enhancing metabolism associated with H(2)O(2) is more effective than enhancing the capacity for superoxide scavenging. Although small, the improvement in the protection of photosynthetic capacity may be sufficient to improve cotton yield in temperate regions with large diurnal temperature fluctuations.

Leaf senescence-like characteristics contribute to cotton's premature photosynthetic decline.

Leaf and canopy photosynthesis of cotton (Gossypium hirsutum L.) declines as the crop approaches cutout, just as the assimilate needs for reproductive growth are peaking. Our objective with this study was to determine whether this decline is due to remobilization of leaf components to support the reproductive growth or due to some cue from the changing environmental conditions during the growing season. Field studies were conducted in 1995-1996 at Stoneville, Mississippi, using six cotton genotypes and two planting dates (early and late), which produced two distinctly different cotton populations reaching cutout at different times. Among the six genotypes were a photoperiod sensitive line (non-flowering) and its counter part which had photoperiod insensitive genes backcrossed four times to the photoperiod sensitive line (flowering). This pair was used to assess the degree that the photosynthetic decline could be attributed to reproductive sink development. Leaf CO(2)-exchange rate (CER) and chlorophyll (Chl) fluorescence measurements were taken in mid-August, a period corresponding to cutout for the early planted plots, and those leaves were collected. Leaf Chl level, soluble protein level, various soluble carbohydrate levels and Rubisco activities were assayed on those leaves. Averaged across years, leaf CER and soluble protein levels were reduced approximately 14% and 18%, respectively, for the early planted compared to the late planted cotton. Neither leaf Chl levels or Chl fluorescence Fv/Fm values for Photosystem II yield were altered by the planting date. In 1996, leaves from the non-flowering line had 12% greater Chl and 20% greater soluble protein levels than the flowering line. However, in 1996, the CER of the early planted non-flowering line was reduced 10% compared to the late planted. Although remobilization of leaf N to reproductive growth appears to be the principle component causing the cutout photosynthetic decline, the data also indicate that environmental factors can play a small role in causing the decline.

Changes in growth and physiology of tobacco and cotton under Ag exposure and recovery: are they of direct or indirect nature?

Responses of tobacco and cotton seedlings to two chemical forms of Ag at various concentrations were studied. Cotton exhibited higher resistance than tobacco to Ag. The application of 1 &mgr;g L(-1) Ag, as AgI or AgNO(3), induced no toxicity symptoms in the growth and photosynthesis of cotton. However, the corresponding concentration negatively affected the growth and physiology of tobacco. On exposure to higher Ag concentrations (10(3) and 5 x 10(3) &mgr;g L(-1) as AgNO(3)), root growth and concentrations of Ca, Mg, K, and Fe were significantly depressed, whereas concomitant Ag accumulation, especially in roots, was increased in both species. The loss of nutrients and chlorophyll was associated with disturbances in photosynthetic function. Because there was no apparent change in Fv/Fm, there is a possibility that the faster rise time was due to an increase in LHC size to the PSII reaction centers. The decreased Fv/Fo reflects the inactivation of chlorophyll associated with the PSII reaction center. Stomatal conductance was decreased less than the CO(2) assimilation, possibly due to the direct and/or indirect effects of Ag ions on stomatal guard cells. After the plants were transferred from the highest Ag concentration to a nutrient solution, recovery of tobacco, cotton morphology, and physiology were observed.http://link.springer-ny. com/link/service/journals/00244/bibs/37n4p480.html</HEA

Non-stomatal factors limit cotton photosynthesis under silverleaf whitefly stress

Reduced plant productivity induced by silverleaf whitefly (SLW), Bemisia argentifolii Bellows and Perring, is often associated with reduced net photosynthetic rate (P n ). This study was aimed at characterizing the effects of SLW on photosynthetic activity in cotton and the underlying mechanisms. Cotton (Gossypium hirsutum L. cv. Siv'on) plants were examined under SLW-infested and non-infested conditions and subjected to measurements of gas exchange, chlorophyll content and chlorophyll fluorescence. SLW infestation significantly reduced the P n of cotton by 22-54% throughout the day as well as throughout most of the examined ranges of photosynthetic photon flux density (PPFD) and CO 2 concentrations. Stomatal conductance was also reduced by SLW injury, while intercellular CO 2 concentration (C i ) was not affected, suggesting that stomatal limitation is not the major factor limiting P n . This conclusion was further supported by estimates of stomatal limitation, based on P n /C i curves, which were not affected by SLW infestation. On the other hand, non-stomatal limitation induced by SLW was over 2-fold higher than stomatal limitation. Chlorophyll a and b contents were not modified by SLW infestation. Fluorescence ratio (F v /F m ) and the effective quantum yield of PSII were reduced by less than 10%; thus, impaired photochemical reaction is probably not the only factor limiting P n under SLW infestation. In conclusion, SLW-induced P n reduction in cotton was due to non-stomatal factors, possibly induced by impaired carbon fixation and/or carbohydrate export.

Cotton Photosynthesis and Carbon Partitioning in Response to Floral Bud Loss Due to Insect Damage

To understand better cotton (Gossypium hirsutum L.) plant compensation for early‐season floral bud (square) loss due to insect damage, a field study was conducted in 1994 and 1995 at Marianna, AR. The control treatment was protected by insecticide applications, while tarnished plant bugs (Lygus lineolaris Palisot de Beauvois) and bollworms (Helicoverpa zea Boddie) were released in the plots of the other treatment three times before flowering. Square abscission at the first sympodial fruiting position was 5 and 33% for the control and infested plants, respectively, and yield was reduced 21% by insect infestation. Insect treatment resulted in 4% more light penetration through the canopy, which may have contributed to the 17% increase in photosynthesis of the eighth main‐stem leaf from the terminal leaf as compared with the control plants. Canopy photosynthesis recorded 4 wk after the initiation of flowering was 21% higher in the infested plants. CO2 labeling showed infestation also resulted in more 14C recovered in the terminal node (terminal leaf plus main stem above the terminal leaf) and less remaining in the branch at the same node as the source leaf, which corresponded to an increase in plant height, although node number was not affected. Since our insect‐induced abscission treatments had similar effects as manual fruit removal treatments reported by others, future studies seem justified in using either approach. Early fruit loss in the U.S. Mid‐south results in changes in carbon exchange and allocation, but poor late‐season growing conditions often prevent yield compensation.