Leaf anatomy and gas exchange in maize and sorghum as related to reduced water availability

Abstract

Climate changes are changing local climates and favoring drought events on several environments. Maize is often recognized as drought-sensitive while sorghum is a recognized drought-tolerant species and these behaviors may be related to anatomical and physiological traits. Thus, the objective of this study was to evaluate the effect of water deficit in the leaf anatomy and gas exchanges as related to growth that attribute specific drought-tolerance traits in sorghum and maize. Plants were obtained from seeds and experiments were conducted in a greenhouse at 25±2°C, in which plants were subjected to three water conditions: field capacity (FC), 75% FC and 50% FC and ten replicates for 60 days. Growth, gas exchange, and anatomical analysis were performed. Data were subjected to analysis of variance and means compared by the Scott-Knott test at P<0.05. Sorghum plants showed no growth or water content limitation under lower water levels but increased intercellular CO2 content was observed. In addition, sorghum showed higher mesophyll area and increased proportion of stomatal cavities under lower water levels. Water limitation rather changed leaf anatomy, including stomatal traits in sorghum plants. Increased stomatal cavities in sorghum grown under water limitation provided conditions for CO2 uptake and the maintenance of growth and water content as increased stomatal chambers may be related to drought-tolerance in this species. Maize plants maize showed significant growth reduction under water limitation as the dry mass and other biometrical parameter were harmed. Water limitation reduced the number leaves, leaf width, leaf thickness, leaf area and mesophyll area of maize plants. No modifications were found in the gas exchange per unit area but these parameters were reduced in the whole plant level. Maize plants showed lower water retention and increased transpiration under water-limited conditions. Maize leaf anatomical modifications under water limitation indicate its incapacity to adjust anatomy to enhance drought-tolerance but were still able to survive under a high growth limitation. Therefore, the leaf intercellular spaces seems to be important for sorghum drought tolerance since these plants showed capacity to change these parameters, particularly the stomatal cavities size, while the drought sensitive maize were unable to promote significant changes in its leaf anatomy to improve drought-tolerance responses.