Abscisic acid-induced elevation of guard cell cytosolic Ca2+ precedes stomatal closure.

STOMATTA allow the diffusion of CO2 into the leaf for photosynthesis and the diffusion of H2O out of the leaf during transpiration1,2. This gaseous exchange is regulated by pairs of guard cells that surround each stomatal pore. During water stress the loss of water through transpiration is reduced in response to abscisic acid3, a naturally occurring plant growth regulator which is also present in certain mammals4, algae5 and fungi6, by the promotion of stomatal closure and inhibition of opening7. This involves alterations to guard cell turgor, causing the cells to shrink and thereby reducing the size of the stomatal pore. These changes are driven by cation and anion effluxes8. It has been proposed that an abscisic acid-dependent increase in the concentration of guard cell cytosolic free calcium triggers the intracellular machinery responsible for stomatal closure9(for a review, see ref. 10), but attempts to test this hypothesis by measuring [45Ca] fluxes have produced equivocal results11. Using the fluorescent calcium indicator fura-2, we report that abscisic acid induces a rapid increase in guard cell cytosolic free Ca2+ in Commelina communisL., and that this increase precedes stomatal closure. These results strongly support the suggestion that Ca2+ is an intracellular second messenger in this response

Stomatal opening in response to the simultaneous increase in vapor pressure deficit and temperature over a 24-h period under constant light in a tropical rainforest of the central Amazon

Stomatal functioning is modulated by several factors and, in most circumstances, stomatal aperture declines with increasing leaf-to-air vapor pressure difference (VPDL) and temperature, but stomatal functioning under the humid conditions of the tropical rainforest understory has been scarcely investigated. The aim of this study was to determine how stomatal conductance of saplings responds to the changing understory temperatures of a tropical rainforest. We measured gas-exchange in four saplings of Guarea carinata (1–2 m tall). On each plant, stomatal conductance (gs), VPDL and leaf temperature were measured continuously at 3-min intervals during 24 h. We used a constant irradiance of 50 µmol m−2 s−1 and nearly constant relative humidity (75.8 ± 1.9%). Within the leaf chamber, leaf temperature over plants varied from 25.8 to 30.7 °C and VPDL from 0.62 to 0.93 kPa. Contrary to expectations, gs increased with the increase in leaf temperature and VPDL, and throughout the 24-h cycle, gs was maximum (0.123 mol m−2 s−1) at midday when temperatures were higher and minimum (0.016 mol m−2 s−1) after midnight, when the lower temperatures were recorded. There was a positive relationship between gs and both leaf temperature (p < 0.0001) and VPDL (p < 0.0001). If global temperature continues to increase as predicted by models, the direct increase in gs of saplings associated with an increase in temperature can be nullified if global warming negatively affects the water balance of plants (e.g. Guarea carinata) in this part of the Amazon. © 2017, Brazilian Society of Plant Physiology

mRNA cap binding proteins: effects on abscisic acid signal transduction, mRNA processing, and microarray analyses.

International audienceThe plant hormone abscisic acid (ABA) intricately regulates a multitude of processes during plant growth and development. Recent studies have established a connection between genes participating in various steps of cellular RNA metabolism and the ABA signal transduction machinery. In this chapter we focus on the plant nuclear mRNA cap binding proteins, CBP20 and CBP80. We summarize and report recent findings on their effects on cellular signal transduction networks and mRNA processing events. ABA hypersensitive 1 (abh1) harbors a gene disruption in the Arabidopsis CBP80 gene. Loss-of-function mutation of ABH1 can also result in an early flowering phenotype in the Arabidopsis accession C24. abh1 revealed noncoding cis-natural antisense transcripts (cis-NATs) at the CONSTANS locus in wild-type plants with elevated cis-NAT expression in the mutant. abh1 also revealed an influence on the splicing of the MADS box transcription factor Flowering Locus C pre-mRNA, which may result in the regulation of flowering time. Furthermore, new experiments analyzing complementation of cpb20 with site-directed cpb20 mutants provide evidence that the CAP binding activity of CBP20 is essential for the observed cbp-associated phenotypes. In conclusion, mutants in genes participating in RNA processing provide excellent tools to uncover novel molecular mechanisms for the regulation of RNA metabolism and of signal transduction networks in wild-type plants