title: Foliar Abscisic Acid-To-Ethylene Accumulation and Response Regulate Shoot Growth Sensitivity to Mild Drought in Wheat.
abstract: Although, plant hormones play an important role in adjusting growth in response to environmental perturbation, the relative contributions of abscisic acid (ABA) and ethylene remain elusive. Using six spring wheat genotypes differing for stress tolerance, we show that young seedlings of the drought-tolerant (DT) group maintained or increased shoot dry weight (SDW) while the drought-susceptible (DS) group decreased SDW in response to mild drought. Both the DT and DS groups increased endogenous ABA and ethylene concentrations under mild drought compared to control. The DT and DS groups exhibited different SDW response trends, whereby the DS group decreased while the DT group increased SDW, to increased concentrations of ABA and ethylene under mild drought, although both groups decreased ABA/ethylene ratio under mild drought albeit at different levels. We concluded that SDW of the DT and DS groups might be distinctly regulated by specific ABA:ethylene ratio. Further, a foliar-spray of low concentrations (0.1 μM) of ABA increased shoot relative growth rate (RGR) in the DS group while ACC (1-aminocyclopropane-1-carboxylic acid, ethylene precursor) spray increased RGR in both groups compared to control. Furthermore, the DT group accumulated a significantly higher galactose while a significantly lower maltose in the shoot compared to the DS group. Taken all together, these results suggest an impact of ABA, ethylene, and ABA:ethylene ratio on SDW of wheat seedlings that may partly underlie a genotypic variability of different shoot growth sensitivities to drought among crop species under field conditions. We propose that phenotyping based on hormone accumulation, response and hormonal ratio would be a viable, rapid, and an early-stage selection tool aiding genotype selection for stress tolerance.
authors.affiliation: Global Wheat Program, International Maize and Wheat Improvement Center (CIMMYT)El Batan, Mexico; Plant Biology Department, Lancaster Environmental Center, Lancaster UniversityLancaster, UK.
authors.forename: Ravi
authors.initials: R
authors.lastname: Valluru
authors.affiliation: Plant Biology Department, Lancaster Environmental Center, Lancaster University Lancaster, UK.
authors.forename: William J
authors.initials: WJ
authors.lastname: Davies
authors.affiliation: Global Wheat Program, International Maize and Wheat Improvement Center (CIMMYT) El Batan, Mexico.
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Reynolds
authors.affiliation: Plant Biology Department, Lancaster Environmental Center, Lancaster University Lancaster, UK.
authors.forename: Ian C
authors.initials: IC
authors.lastname: Dodd
keywords: abscisic acid; drought; ethylene; growth sensitivity; hormonal ratio; mild drought