Influence of Low Air Humidity and Low Root Temperature on Water Uptake, Growth and Aquaporin Expression in Rice Plants

Abstract

The effects of low air humidity and low root temperature (LRT) on water uptake, growth and aquaporin gene expression were investigated in rice plants. The daily transpiration of the plants grown at low humidity was 1.5- to 2-fold higher than that at high humidity. LRT at 13°C reduced transpiration, and the extent was larger at lower humidity. LRT also reduced total dry matter production and leaf area expansion, and the extent was again larger at lower humidity. These observations suggest that the suppression of plant growth by LRT is associated with water stress due to decreased water uptake ability of the root. On the other hand, the net assimilation rate was not affected by low humidity and LRT, and water use efficiency was larger for LRT. We found that low humidity induced coordinated up-regulation of many PIP and TIP aquaporin genes in both the leaves and the roots. Expression levels of two root-specific aquaporin genes, OsPIP2;4 and OsPIP2;5, were increased significantly after 6 and 13 d of LRT exposure. Taken together, we discuss the possibility that aquaporins are part of an integrated response of this crop to low air humidity and LRT.

Rice Plants Sense Daily Weather and Regulate Aquaporin Gene Expressions in the Roots -Close correlation with potential evaporation-

“…In our previous study (Kuwagata et al, 2012) on rice grown hydroponically in controlled growth chambers, exposure of the shoots to low air humidity induced coordinated up-regulation of aquaporin genes not only in the roots, but also in the leaf blades. We are currently investigating how rice plants growing in paddy fields perceive daily weather signals and then regulate gene expression in shoots and roots for daily optimization of whole-plant hydraulics.…”

“…Among 13 aquaporins examined, positive and significant (p < 0.05) correlation was observed in 5 PIPs (OsPIP1;2,OsPIP1;3,OsPIP2;1,OsPIP2;4,OsPIP2;5) and 1 TIP (OsTIP2;1). All of them, except OsPIP1;2 and OsPIP2;1, are highly root specific (Sakurai et al, 2005;Sakurai et al, 2008;Sakurai-Ishikawa et al, 2011;Kuwagata et al, 2012). The highest correlation was observed in OsPIP2;5 (R = 0.86, p < 0.01).…”

“…Organ-specific localization, and water transport activity measured by stopped-flow light scattering are summarized according to the references below (organs in Italic, unpublished data). 1, Sakurai et al (2005); 2, Sakurai et al (2008); 3, Sakurai-Ishikawa et al (2011);4, Muto et al (2011); 5, Kuwagata et al (2012).…”

“…Up-regulation of root aquaporins depending on an increased evaporative demand has directly been reported for a limited number of plant species, including rice (Sakurai-Ishikawa et al, 2011;Kuwagata et al, 2012), Arabidopsis (Levin et al, 2009) and hybrid popular (Almedia-Rodriguez et al, 2011, Laur andHacke, 2013). Close relation between aquaporin abundance in the roots and transpiration (or stomatal conductance) has recently been suggested in grapevine (Gambetta et al, 2012, Perrone et al, 2012.…”

“…Extensive studies of the effects of the water conditions in the root zone (such as soil water deficit, high salinity, high osmolality, and flooding) on the function and regulation of aquaporins suggested marked effects of these environmental stresses on aquaporin abundance in the roots (Tournaire-Roux et al, 2003;Jang et al, 2004;Alexandersson et al, 2005;Boursiac et al, 2005;Bramley et al, 2007;Li et al, 2008;Mahdieh et al, 2008). However, relatively little information is available on how root aquaporins respond to fluctuating evaporative demand (Levin et al, 2009;Sakurai-Ishikawa et al, 2011;Almeida-Rodriguez et al, 2011;Kuwagata et al, 2012;Vandeleur et al, 2014).…”