The contribution of PIP2-type aquaporins to photosynthetic response to increased vapour pressure deficit.

David Israel,Charles R Warren,Shanjida Khan,Janusz J Zwiazek,T Matthew Robson,Ian Dodd

doi:10.1093/jxb/erab187

Abstract

The roles of different plasma membrane aquaporins (PIPs) in leaf-level gas exchange of Arabidopsis thaliana were examined using knockout mutants. Since multiple Arabidopsis PIPs are implicated in CO2 transport across cell membranes, we focused on identifying the effects of the knockout mutations on photosynthesis, and whether they are mediated through the control of stomatal conductance of water vapour (gs), mesophyll conductance of CO2 (gm), or both. We grew Arabidopsis plants in low and high humidity environments and found that the contribution of PIPs to gs was larger under low air humidity when the evaporative demand was high, whereas any effect of a lack of PIP function was minimal under higher humidity. The pip2;4 knockout mutant had 44% higher gs than wild-type plants under low humidity, which in turn resulted in an increased net photosynthetic rate (Anet). We also observed a 23% increase in whole-plant transpiration (E) for this knockout mutant. The lack of functional plasma membrane aquaporin AtPIP2;5 did not affect gs or E, but resulted in homeostasis of gm despite changes in humidity, indicating a possible role in regulating CO2 membrane permeability. CO2 transport measurements in yeast expressing AtPIP2;5 confirmed that this aquaporin is indeed permeable to CO2.

Highlights

Water flow across membranes, and through the plant, is dioxide (CO2) and oxygen (O2) (Agre et al, 1993; Heckwolf regulated by aquaporins, which in addition to water may et al, 2011; Zwiazek et al, 2017)
Since multiple Arabidopsis plasma membrane intrinsic protein (PIP) are implicated in CO2 transport across cell membranes, we focused on identifying the effects of the knockout mutations on photosynthesis, and whether they are mediated through the control of stomatal conductance of water vapour, mesophyll conductance of CO2, or both
In addition to the traditional parameters extracted from photosynthetic light–response curves, we used generalized additive mixed modelling (GAMM) which enabled us to analyse the mutants’ stomatal response to changing light intensities.These analyses confirmed the differences in the shape of light–response curves, which were significant for an increased net photosynthetic rate (Anet), corroborating the significant difference we report in φ, as well as gs in pip2;5 compared with the wild type (WT)

Summary

Introduction

Through the plant, is dioxide (CO2) and oxygen (O2) (Agre et al, 1993; Heckwolf regulated by aquaporins, which in addition to water may et al, 2011; Zwiazek et al, 2017). PIPs are involved in a variety of processes regulating plant water flow starting from the root through the stem, as well as into and out of the leaves (Javot et al, 2003; Fraysse et al, 2005; Da Ines et al, 2010; Ben Baaziz et al, 2012; Gambetta et al, 2013). Based on their phylogeny, PIPs are further divided into two subgroups, the PIP1s and PIP2s, with five and eight isoforms, respectively (Johanson et al, 2001). Since all PIPs have identical selectivity filters (Wallace and Roberts, 2004), which are major determinants of substrate permeability, it is reasonable to assume that other isoforms of the PIP1 and PIP2 subgroups may contribute to CO2 diffusion across the plasma membrane and affect gm in leaves

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