Phospholipase D (PLD) is involved in responses to abiotic stress and abscisic acid (ABA) signaling. To investigate the roles of two Arabidopsis (Arabidopsis thaliana) PLDs, PLDa1 and PLDd, in ABA signaling in guard cells, we analyzed ABA responses in guard cells using Arabidopsis wild type, plda1 and pldd single mutants, and a plda1 pldd double mutant. ABA-induced stomatal closure was suppressed in the plda1 pldd double mutant but not in the pld single mutants. The plda1 and pldd mutations reduced ABAinduced phosphatidic acid production in epidermal tissues. Expression of either PLDa1 or PLDd complemented the double mutant stomatal phenotype. ABA-induced stomatal closure in both plda1 and pldd single mutants was inhibited by a PLD inhibitor (1-butanol ), suggesting that both PLDa1 and PLDd function in ABA-induced stomatal closure. During ABA-induced stomatal closure, wild-type guard cells accumulate reactive oxygen species and nitric oxide and undergo cytosolic alkalization, but these changes are reduced in guard cells of the plda1 pldd double mutant. Inward-rectifying K + channel currents of guard cells were inhibited by ABA in the wild type but not in the plda1 pldd double mutant. ABA inhibited stomatal opening in the wild type and the pldd mutant but not in the plda1 mutant. In wild-type rosette leaves, ABA significantly increased PLDd transcript levels but did not change PLDa1 transcript levels. Furthermore, the plda1 and pldd mutations mitigated ABA inhibition of seed germination. These results suggest that PLDa1 and PLDd cooperate in ABA signaling in guard cells but that their functions do not completely overlap.

Nitrogen (N) and carbon (C) are essential elements for plant growth and crop yield. Thus, improved N and C utilisation contributes to agricultural productivity and reduces the need for fertilisation. In the present study, we find that overexpression of a single rice gene, Oryza sativa plasma membrane (PM) H+-ATPase 1 (OSA1), facilitates ammonium absorption and assimilation in roots and enhanced light-induced stomatal opening with higher photosynthesis rate in leaves. As a result, OSA1 overexpression in rice plants causes a 33% increase in grain yield and a 46% increase in N use efficiency overall. As PM H+-ATPase is highly conserved in plants, these findings indicate that the manipulation of PM H+-ATPase could cooperatively improve N and C utilisation, potentially providing a vital tool for food security and sustainable agriculture.

Isothiocyanates, nitriles, and thiocyanates are degradation products of glucosinolates in crucifer plants. In this study, we investigated the stomatal response to allyl isothiocyanate (AITC), 3-butenenitrile (3BN), and ethyl thiocyanate (ESCN) in Arabidopsis. AITC, 3BN, and ESCN induced stomatal closure in the wild type and the atrbohD atrbohF mutant. Stomatal closure was inhibited by catalase and salicylhydroxamic acid (SHAM). The degradation products induced extracellular reactive oxygen species (ROS) production in the rosette leaves, and intracellular ROS accumulation, NO production, and cytosolic free calcium concentration ([Ca(2+)]cyt) oscillations in guard cells, which were inhibited by SHAM. These results suggest that glucosinolate degradation products induce stomatal closure accompanied by extracellular ROS production mediated by SHAM-sensitive peroxidases, intracellular ROS accumulation, and [Ca(2+)]cyt oscillation in Arabidopsis.