Different Leaf Anatomical Responses to Water Deficit in Maize and Soybean

Abstract

The stomata on leaf surfaces control gas exchange and water loss, closing during dry periods to conserve water. The distribution and size of stomatal complexes is determined by epidermal cell differentiation and expansion during leaf growth. Regulation of these processes in response to water deficit may result in stomatal anatomical plasticity as part of the plant acclimation to drought. We quantified the leaf anatomical plasticity under water-deficit conditions in maize and soybean over two experiments. Both species produced smaller leaves in response to the water deficit, partly due to the reductions in the stomata and pavement cell size, although this response was greater in soybean, which also produced thicker leaves under severe stress, whereas the maize leaf thickness did not change. The stomata and pavement cells were smaller with the reduced water availability in both species, resulting in higher stomatal densities. Stomatal development (measured as stomatal index, SI) was suppressed in both species at the lowest water availability, but to a greater extent in maize than in soybean. The result of these responses is that in maize leaves, the stomatal area fraction (fgc) was consistently reduced in the plants grown under severe but not moderate water deficit, whereas the fgc did not decrease in the water-stressed soybean leaves. The water deficit resulted in the reduced expression of one of two (maize) or three (soybean) SPEECHLESS orthologs, and the expression patterns were correlated with SI. The vein density (VD) increased in both species in response to the water deficit, although the effect was greater in soybean. This study establishes a mechanism of stomatal development plasticity that can be applied to other species and genotypes to develop or investigate stomatal development plasticity.

Trait variation and performance across varying levels of drought stress in cultivated sunflower (Helianthus annuus L.)

“…Overall, as expected, the leaf area of individual leaves decreased in response to drought and leaf mass per area increased. For stomatal traits, average stomatal density increased and average stomatal pore length decreased consistent with other responses to drought ( Yu et al 2008 ; Sack and Scoffoni 2013 ; Sun et al 2014 ; Franks et al 2015 ; Carlson et al 2016 ; Ouyang et al 2017 ; Bresta et al 2018 ; Lei et al 2018 ; Mano et al 2023 ). However, other studies, including several for sunflower, documented no consistent effect on stomatal density ( Xu and Zhou 2008 ; Doheny-Adams et al 2012 ; Sack and Scoffoni 2013 ; Shahinnia et al 2016 ; Cardoso et al 2018 b; Tran et al 2024 ; Fig.…”

“…Minor vein length per area increased in response to drought, consistent with phenotypic responses to drought in some other herbaceous species ( Lei et al 2018 ; Wang et al 2018 ; Dhakal et al 2021 ; Mano et al 2023 ). An increase in vein density is likely associated with greater hydraulic conductance and the maintenance of hydraulic function may be critical for plant survival under drought ( Yao et al 2021 ).…”

“…For intraspecific variation in crops and other herbaceous species, acclimation to drought generally results in development of new leaves with higher stomatal density and/or smaller stomatal size, as well as higher vein length density and hydraulic conductance (e.g. Yu et al 2008 ; Xu and Zhou 2008 ; Doheny-Adams et al 2012 ; Sack and Scoffoni 2013 ; Sun et al 2014 ; Franks et al 2015 ; Carlson et al 2016 ; Shahinnia et al 2016 ; Ouyang et al 2017 ; Wang et al 2018 ; Bresta et al 2018 ; Lei et al 2018 ; Dhakal et al 2021 ; Mano et al 2023 ; Figure S2 ), but not necessarily for sunflower ( Cardoso et al 2018 b; Janzen et al 2023 ; Tran et al , 2024 ). There is also some support for the expected negative correlation between stomatal density and stomatal size, as well as positive correlations between stomatal density and vein length density ( Doheny-Adams et al 2012 ; Carins Murphy et al 2014 ; Sun et al 2014 ; Shahinnia et al 2016 ; Xiong et al 2018 ; Bresta et al 2018 ; Lei et al 2018 ; but see Milla et al 2013 ).…”

Assessment of Drought Responses of Wild Soybean Accessions at Different Growth Stages

“…In soybean, smaller stomata have been reported in response to water deficit [46][47][48], but changes in the stomatal density in response to water deficit are variable, as various reports show unchanged, increased, or decreased stomatal density [46][47][48][49][50]. Greater stomatal density was associated with a higher transpiration rate and increased water loss [17][18][19]51].…”

Application of electronic nose and machine learning used to detect soybean gases under water stress and variability throughout the daytime

“…This variation is primarily caused by water stress which leads to the closure of stomata, ultimately resulting in an increase in the leaf temperature. Mano et al (2023) found in their works that water deficit led to reductions in stomata size and density in both maize and soybean leaves. These findings collectively support the idea that water stressinduced stomata closure contributes to an increase in soybean leaf temperature.…”