Leaf Epidermal Plasticity in Response to Water Deficit Stress
Abstract
Anthropogenic climate change is projected to worsen the frequency and intensity of waterdeficit periods, which will reduce agricultural yields and the range of native plant species. Therefore, multiple research avenues focus on the mechanisms of plant responses to water deficit. We investigated the anatomy of stomata, which are small pores on leaf surfaces through which water is transpired to the atmosphere, to understand how stomatal anatomy changes under waterstress conditions. Previous work showed that repression of stomatal development by knockout of GT2-LIKE 1 (GTL1) results in fewer stomata and improved drought survival. We hypothesized that GTL1, as a transcription factor, also regulates other drought responsive pathways. We performed a transcriptomic study that found GTL1 represses genes in the biosynthesis of flavonoids, anthocyanin, and putrescine. All three compounds have been shown to promote drought tolerance. We also observed that water-stress-induced downregulation of GTL1 results in inhibited stomatal development. We next aimed to quantify if stomatal development is similarly inhibited in response to water deficit in other species and the anatomical and physiological implications of stomatal development inhibition. We investigated water-deficit-induced stomatal plasticity in maize and soybean, as important crop species, and river birch, silver maple, and eastern redbud, as common Midwestern trees. The overall leaf surface occupied by stomata (fgc) decreased in some species (maize, birch, redbud), but not others (soybean, maple), although stomata were smaller in water-stressed leaves of all species. fgc decreased because stomatal development inhibition prevented stomatal density from increasing in smaller water-stressed leaves. In maize and soybean, stomatal development inhibition occurs through downregulation of orthologues of the stomatal development gene SPEECHLESS. We also found that fgc reduction in redbud prevented the recovery of stomatal conductance after drought, but unlike birch and maple, redbud leaves maintained water-use efficiency comparable to well-watered plants. A meta-analysis of published literature on water-deficit-induced stomatal anatomical plasticity further supported our hypothesis that stomatal development inhibition contributes to fgc plasticity. The meta-analysis also showed that severe water deficits are required for fgcplasticity. In conclusion, plasticity of stomatal anatomy is highly variable across species and genotypes. However, inhibition of stomatal development in some plants under water-deficit stress reduces the epidermal area occupied by stomata, which in turn may facilitate water conservation.
Degree
Ph.D.
Advisors
Mickelbart, Purdue University.
Subject Area
Climate Change|Physiology|Agronomy|Bioinformatics|Botany|Genetics|Water Resources Management
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