Changes in aerenchyma, leaf intercellular spaces, growth, photosynthesis, anatomy and nutrient uptake in maize and sorghum caused by drought

Abstract

Water loss causes changes in vital plant processes, such as transpiration and photosynthesis, and is associated with severe climate change, which increases the occurrence of drought. In addition, the main effects are related to the loss of dry mass, reducing plant growth and production. The current challenge is to explore different mechanisms of drought tolerance in plants such as maize and sorghum, which are considered drought-sensitive and drought- tolerant, respectively. This study aimed to evaluate the effects of water restriction on the morphophysiology, anatomy along the leaf axis, and root development of maize and sorghum in relation to growth and gas exchange. Plants were grown from seeds, and experiments were conducted in a greenhouse at 25 ± 2 °C. Maize and sorghum plants were subjected to water restriction, and growth, gas exchange, and quantitative anatomical analyses of leaves and roots were performed. Data were subjected to analysis of variance, and means were compared using the Scott-Knott test (P < 0.05). Water deficit was a limiting factor for maize, leading to reductions in leaf area, leaf thickness, biomass, water use efficiency, xylem vessel diameter, bundle sheath area, and gas exchange, whereas sorghum remained largely unaffected, except for water use efficiency, xylem diameter, and bundle sheath area, which increased under the same conditions. These responses were associated with an increase in intercellular spaces in sorghum leaves. Additionally, the middle region of the sorghum leaf exhibited higher physiological parameters compared to other regions, and the leaf base showed increased ΦPSII, Fv/Fm, and ETR. Sorghum maintained stomatal function compared to maize. In the roots, the piliferous zone exhibited more pronounced changes than the maturation zone under water restriction. Sorghum showed greater root elongation, contributing to an increase in aerenchyma formation. Despite this, there were no significant effects on water and nutrient absorption in sorghum, unlike in maize. These traits contributed to sorghum's drought tolerance, whereas maize failed to make similar adjustments. Overall, drought had a detrimental effect on maize, as it reduced most evaluated parameters and hindered the adjustment of intercellular spaces within leaves and roots, which appears to be crucial for drought tolerance in sorghum. Furthermore, most physiological traits varied along the leaf axis in both species, with the median leaf region exhibiting the highest functionality.