|Do Carmo Silva, Anaelisabete|
|Andrade-Sanchez, Pedro -|
Submitted to: Environmental and Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 9, 2012
Publication Date: May 9, 2012
Citation: Do Carmo Silva, A., Gore, M.A., Andrade-Sanchez, P., French, A.N., Hunsaker, D.J., Salvucci, M.E. 2012. Decreased CO2 availability and inactivation of Rubisco limit photosynthesis in cotton plants under heat and drought stress in the field. Environmental and Experimental Botany. 83:1-11. Interpretive Summary: In the process of photosynthesis, plants convert light into chemical energy. The energy produced by photosynthesis is then used to synthesize food, fuel and fiber; the products that are harvested as agricultural yield. Drought and heat stress inhibit photosynthesis, reducing the overall yield of the plants. To understand how photosynthesis is affected by drought and heat stress under field conditions, various varieties of Pima cotton were grown under normal and reduced irrigation. Leaf temperatures, relative water content, photosynthesis and other physiological parameters were measured over the season using hand-held and high throughput, remote-sensing instruments. The data showed that cotton varieties differed in their response to drought and that the more drought-sensitive varieties exhibited greater susceptibility to heat stress. The biochemical basis for this increased susceptibility to heat stress was identified as a metabolic limitation caused by inactivation of the carbon dioxide fixing enzyme Rubisco. These data provide new insights into the physiological and biochemical responses of plants to drought and heat stress under field conditions. The insights gained and the high throughput methods developed in this study can be used to guide breeding and selection for more heat- and drought-tolerant cotton and for developing new cotton varieties that use less water.
Technical Abstract: Heat and drought stresses are often coincident and constitute major factors limiting global crop yields. Selection of cultivars with superior tolerance to 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 hot and dry conditions, four cotton (Gossypium barbadense L.) cultivars with differential physiological responses to heat stress, Monseratt Sea Island (MS), Pima 32 (P32), Pima S-6 (S6) and Pima S-7 (S7), were grown under well-watered (WW) and water-limited (WL) conditions at a field site in central Arizona. Significant differences in canopy temperatures and leaf relative water content under WL conditions indicated that of the four cultivars, MS was the most drought-sensitive and S6 was the most drought-tolerant. Under WW conditions, net CO2 assimilation (A) and stomatal conductance (gs) were similar for all four cultivars. In contrast, both A and gs decreased and leaf temperatures increased under WL conditions, with MS exhibiting the most change. The response of net photosynthesis to the intercellular CO2 concentration (A-Ci) showed that, along with stomatal closure, non-stomatal factors associated with heat stress also limited photosynthesis under WL conditions, especially in the most drought-sensitive cultivar. Decreased Rubisco activation was associated with the extent of these limitations. Taken together, these data reveal the complex relationship between water availability and heat stress for field-grown cotton plants in a semi-arid environment, with both diffusive and biochemical limitations contributing to decreased photosynthetic performance under hot, arid conditions.