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Abstract
pH is an important factor regulating plant growth. Here, we found that rice was better adapted to low pH than alkaline conditions, as its growth was severely inhibited at high pH, with shorter root length and an extreme biomass reduction. Under alkaline stress, the expression of genes for ethylene biosynthesis enzymes in rice roots was strongly induced by high pH and exogenous ethylene precursor ACC and ethylene overproduction in etol1-1 mutant aggravated the alkaline stress-mediated inhibition of rice growth, especially for the root elongation with decreased cell length in root apical regions. Conversely, the ethylene perception antagonist silver (Ag+) and ein2-1 mutants could partly alleviate the alkaline-induced root elongation inhibition. The H+-ATPase activity was extremely inhibited by alkaline stress and exogenous ACC. However, the H+-ATPase-mediated rhizosphere acidification was enhanced by exogenous Ag+, while H+ efflux on the root surface was extremely inhibited by exogenous ACC, suggesting that ethylene negatively regulated H+-ATPase activity under high-pH stress. Our results demonstrate that H+-ATPase is involved in ethylene-mediated inhibition of rice growth under alkaline stress.
Highlights
Alkaline soils limit the survival of most plants and agricultural productivity
After the seedlings were exposed to pH 6, 7 or 8 nutrition solutions for 30 days, the rice growth was severely inhibited by the alkaline stress, with shorter plant height and root length than at pH 6 (Figures 1A,B), resulting in dramatic biomass reduction (Figure 1D)
These results suggest that the H+ efflux mediated by H+-ATPase was inhibited under alkaline stress, which may be post-transcriptionally regulated by the H+-ATPase activity level
Summary
Alkaline soils limit the survival of most plants and agricultural productivity. Plant roots are the first organ that perceives soil alkalinity, which inhibits root elongation (Fuglsang et al, 2007; Xu et al, 2012; Li et al, 2015). H+-ATPase releases protons from cells to the apoplast, which has important roles in nutrient uptake (Palmgren, 2001; Krajinski et al, 2014), stomatal opening (Wang et al, 2014), polar transport of auxin and cell growth (Rober-Kleber et al, 2003). Acidification of the cell walls by H+-ATPase-mediated H+ excretion across the plasma membrane is critical for root elongation (Cosgrove, 2005; Sánchez-Rodríguez et al, 2010). A low apoplastic pH could increase the activity of expansins in the cell wall and cause cell expansion (Cosgrove, 2000). In the acid growth theory of plant cell elongation, auxin promotes cell elongation
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