K. R. Reddy

Abscisic Acid and Abiotic Stress Tolerance in Crop Plants

Abiotic stress is a primary threat to fulfill the demand of agricultural production to feed the world in coming decades. Plants reduce growth and development process during stress conditions, which ultimately affect the yield. In stress conditions, plants develop various stress mechanism to face the magnitude of stress challenges, although that is not enough to protect them. Therefore, many strategies have been used to produce abiotic stress tolerance crop plants, among them, abscisic acid (ABA) phytohormone engineering could be one of the methods of choice. ABA is an isoprenoid phytohormone, which regulates various physiological processes ranging from stomatal opening to protein storage and provides adaptation to many stresses like drought, salt, and cold stresses. ABA is also called an important messenger that acts as the signaling mediator for regulating the adaptive response of plants to different environmental stress conditions. In this review, we will discuss the role of ABA in response to abiotic stress at the molecular level and ABA signaling. The review also deals with the effect of ABA in respect to gene expression.

Photosynthesis and fluorescence responses of C4 plant Andropogon gerardii acclimated to temperature and carbon dioxide

Increase in both atmospheric CO2 concentration [CO2] and associated warming are likely to alter Earths’ carbon balance and photosynthetic carbon fixation of dominant plant species in a given biome. An experiment was conducted in sunlit, controlled environment chambers to determine effects of atmospheric [CO2] and temperature on net photosynthetic rate (PN) and fluorescence (F) in response to internal CO2 concentration (Ci) and photosynthetically active radiation (PAR) of the C4 species, big bluestem (Andropogon gerardii Vitman). Ten treatments were comprised of two [CO2] of 360 (ambient, AC) and 720 (elevated, EC) µmol mol−1 and five day/night temperature of 20/12, 25/17, 30/22, 35/27 and 40/32 °C. Treatments were imposed from 15 d after sowing (DAS) through 130 DAS. Both F-PN/Ci and F-PN/PAR response curves were measured on top most fully expanded leaves between 55 and 75 DAS. Plants grown in EC exhibited significantly higher CO2-saturated net photosynthesis (Psat), phosphoenolpyruvate carboxylase (PEPC) efficiency, and electron transport rate (ETR). At a given [CO2], increase in temperature increased Psat, PEPC efficiency, and ETR. Plants grown at EC did not differ for dark respiration rate (RD), but had significantly higher maximum photosynthesis (Pmax) than plants grown in AC. Increase in temperature increased Pmax, RD, and ETR, irrespective of the [CO2]. The ability of PEPC, ribulose-1,5-bisphosphate carboxylase/oxygenase, and photosystem components, derived from response curves to tolerate higher temperatures (>35 °C), particularly under EC, indicates the ability of C4 species to sustain photosynthetic capacity in future climates.

Using MODIS LST data for high-resolution estimates of daily air temperature over Mississippi

Three datasets of surface and 2-m air temperature (MODIS LST gridded data, North American Regional Reanalysis surface fields, and meteorological observations from surface stations) with different spatial resolution ranging from a field scale to 32-km model grid have been used to evaluate a statistical relationship between Land Surface Temperature (LST) and daily 2-m maximum and minimum air temperature Ta. The datasets cover Mississippi and adjacent states for the period from June 2000 to September 2004. A comparison between correlations produced by MODIS LST versus observed Tmax and Reanalysis LST versus observed Tmax (surface and air temperature) were performed to assess effects of the averaging scale and the diurnal cycle. Seasonal changes in correlation pattern between December, January, and February (DJF) and June, July, and August (JJA) are revealed and examined.

Exogenous Application of Glycinebetaine Facilitates Maize (Zea mays L.) Growth under Water Deficit Conditions

Aims: To determine whether the exogenous application of glycinebetaine (GB) can ameliorate the effects of water deficit on maize growth and physiological processes. Study Design: Split plot design with water deficit being the main plot factor and GB application being the subplot factor. Treatment was a combination of water deficit level and GB application with 3 replications. Place and Duration of Study: R.R. Foil Plant Science Research Center, Mississippi State University, Mississippi State, MS, USA between May and July 2010. Methodology: A pot experiment was conducted using 31-d old ‘TV25R19’ maize irrigated with 750 ml pot day (WW: well-watered), 450 mL potday (WD60, 60% of WW) and 300 mL potday (WD40, 40% of WW) grown with or without GB application at each stress level. GB was applied as a foliar spray every 5 days at a rate of 4 kg ha. Soil moisture content and leaf water potential, growth, biomass, and gas exchange parameters were measured in response to the treatment variables. Results: Significant GB and water deficit main effects were observed for plant height (PH), leaf dry weight (LDW), ear dry weight (EDW) and total dry weight (TDW) (P  0.05) while Research Article American Journal of Experimental Agriculture, 3(1): 1-13, 2013 2 GB main effects alone were observed for node number (NN) and stem dry weight (SDW) (P  0.05). GB application increased leaf area (LA) (5,454 cm plant) in WD60 plants relative to untreated plants. No GB effect was seen under other treatment combinations at 10 or 20 days after treatment (DAT) measurements. GB did not increase stomatal conductance or transpiration at 10 or 20 DAT in plants subjected to water deficit. GB application resulted in leaf water potential values in the WD60 treatment that were statistically similar to the well-watered plants. Volumetric soil water content did not change with foliar GB application across water deficit treatments except under mild stress after 18 DAT, where soil moisture was higher for GB treated plants. Conclusion: GB’s effect was most evident in plants from the WD60 treatment. GB application significantly improved PH, LA, LDW, SDW, EDW and TDW and did not influence NN under WD60 conditions.

Maize growth and developmental responses to temperature and ultraviolet-B radiation interaction

Plant response to the combination of two or more abiotic stresses is different than its response to the same stresses singly. The response of maize (Zea mays L.) photosynthesis, growth, and development processes were examined under sunlit plant growth chambers at three levels of each day/night temperatures (24/16°C, 30/22°C, and 36/28°C) and UV-B radiation levels (0, 5, and 10 kJ m−2 d−1) and their interaction from 4 d after emergence to 43 d. An increase in plant height, leaf area, node number, and dry mass was observed as temperature increased. However, UV-B radiation negatively affected these processes by reducing the rates of stem elongation, leaf area expansion, and biomass accumulation. UV-B radiation affected leaf photosynthesis mostly at early stage of growth and tended to be temperature-dependent. For instance, UV-B radiation caused 3–15% decrease of photosynthetic rate (PN) on the uppermost, fully expanded leaves at 24/16°C and 36/28°C, but stimulated PN about 5–18% at 30/22°C temperature. Moreover, the observed UV-B protection mechanisms, such as accumulation of phenolics and waxes, exhibited a significant interaction among the treatments where these compounds were relatively less responsive (phenolics) or more responsive (waxes) to UV-B radiation at higher temperature treatments or vice versa. Plants exposed to UV-B radiation produced more leaf waxes except at 24/16°C treatment. The detrimental effect of UV-B radiation was greater on plant growth compared to the photosynthetic processes. Results suggest that maize growth and development, especially stem elongation, is highly sensitive to current and projected UV-B radiation levels, and temperature plays an important role in the magnitude and direction of the UV-B mediated responses.

Genotypic variability among cotton cultivars for heat and drought tolerance using reproductive and physiological traits

Development of rapid and inexpensive screening tools for heat and drought stress tolerance is needed and will be helpful in cotton breeding programs and selecting cultivars for a niche environment. In this study, several pollen-based traits at optimum and high temperatures and physiological parameters measured during the boll-filling period were used to evaluate variability among the cultivars for heat and drought stresses. Principal component analysis and drought stress response index methods were used to categorize cotton cultivars into three heat and drought tolerant clusters. Based on the combined analysis, PX532211WRF has been identified as heat- and drought-tolerant, and would be expected to perform better under both heat- and drought-stressed environments. A poor correlation between reproductive and physiological indices indicates that screening breeders have to use different traits to screen cultivars for reproductive and vegetative tolerance. Identified traits could serve as valuable screening tools in cotton breeding programs aimed at developing genotypes to a changing climate. Moreover, cultivar-dependent relative scores will aid in the identification of cultivars best suited to niche environments to alleviate the influences of abiotic stresses at both vegetative and reproductive stages.

Genotypic variation of soybean and cotton crops in their response to UV-B radiation for vegetative growth and physiology

The effects of ultraviolet-B (UV-B) radiation on seven cotton (DP 458B/RR, DP 5415RR, FM 832B, NuCOTN 33B, Pima S7, Tamcot HQ95 and SG 521B) and six soybean (D 88-5320, D 90-9216, Stalwart III, PI 471938, DG 5630RR, and DP 4933RR) genotypes were evaluated in sunlit controlled-environment chambers under optimum water, nutrient and temperature conditions. Plants were exposed to UV-B radiation levels of 4, 8, 12 and 16 (cotton); and 0, 5, 10 and 15 kJ m-2 d-1 (soybean) from emergence to 31 days after sowing (DAS) in cotton and 58 DAS in soybean. Growth and physiological responses were measured and quantified. Higher UV-B significantly reduced dry matter production, plant height, leaf area in all genotypes compared to control plants in both the crops; however, significant genotypic differences in the magnitude of the UV-B induced changes were observed. Cumulative stress response index (CSRI), the sum of individual percentage of relative responses to UV-B radiation, total response index (TRI), the sum of CSRI at all the levels of UV-B for each genotype were used to classify the genotypes for UV-B tolerance. The TRI ranged from -195 to - 417 in soybean and -40 to -524 in cotton. Based on TRI, cotton genotypes, DP 458B/RR, NuCOTN 33B and DP 5415RR were classified as tolerant; Pima S7, and FM 832B as intermediate; and SG 521B, and Tamcot HQ95 as sensitive. In soybean, PI 471938 was tolerant; Stalwart III and D 88-5320 as intermediate; DG 5630RR, DP 4933RR and D 90-9216 were identified as sensitive genotypes. Even though, relative injury of the leaves decreased and phenolic concentrations increased with increasing UV-B in all genotypes, there were no significant correlations between these parameters and TRI of the genotypes in either crop. The observed genotypic differences suggest that it is possible to breed and select UV-B tolerant soybean and cotton genotypes for a niche environment.