A comparison of aquaporin function in mediating stomatal aperture gating among drought-tolerant and sensitive varieties of rice (Oryza sativa L.)

Abstract

Climate change drastically affects the cultivation of rice, and its production is affected significantly by water stress. Adaptation of a plant to water deficit conditions is orchestrated by efficient water uptake and a stringently regulated water loss. Transpiration remains the major means of water loss from plants and is mediated by microscopic pores called stomata. Stomatal aperture gating is facilitated by ion channels and aquaporins (AQPs) which regulate the turgidity of the guard cells. In a similar manner, efficient water uptake by the roots is regulated by the presence of AQPs in the plasma membrane of root cells. In this study, we compare the efficiency of transmembrane water permeability in guard cells and root protoplasts from drought-tolerant and sensitive varieties of Oryza sativa L. In this report, we studied the transmembrane osmotic water permeability (P) of guard cell and root protoplasts of drought-sensitive and tolerant cultivars. The guard cells isolated from the drought-sensitive lowland rice variety ADT-39 show significant low osmotic permeability than the drought-tolerant rice varieties of Anna (lowland) and Dodda Byra Nellu (DBN) (upland local land rice). There is no significant difference in relative gene expression patterns of PIPs (Plasma membrane Intrinsic Proteins "PIP1" and "PIP2" subfamilies) in guard cells isolated from ADT-39 and Anna. While the expression levels of AQP genes remain the same between ADT-39 and Anna, there is a drastic difference in their osmotic permeability in the guard cells in spite of a higher number of stomata in Anna and DBN, hinting at a more efficient gating mechanism of AQP in the stomata of the drought-tolerant varieties studied.

Enhanced Drought Stress Tolerance by the Arbuscular Mycorrhizal Symbiosis in a Drought-Sensitive Maize Cultivar Is Related to a Broader and Differential Regulation of Host Plant Aquaporins than in a Drought-Tolerant Cultivar

“…However, AM regulation of aquaporins in the drought-tolerant genotype was weaker, and only three aquaporins ( ZmPIP1;6, ZmPIP2;2 , and ZmTIP4;1 ) were found to be altered. It is noteworthy that these three aquaporins were even up-regulated under well-watered conditions, which is an opposite behavior than in the sensitive genotype, similar to results reported by Liu et al (2013) or Vinnakota et al (2016) in two rice varieties and two Malus species with contrasting drought sensitivity. Also, upland rice and lowland rice with different responses to drought were compared to study the role of aquaporins in drought resistance and authors found important differences in PIP aquaporin transcriptional regulation in both types of rice (Lian et al, 2006).…”

“…During drought stress episodes, water conservation is critical for plant survival and productivity, and is achieved by an efficient uptake and stringently regulated water loss, in which aquaporins participate (Vinnakota et al, 2016). Our results in the drought-sensitive cultivar are in line with the hypothesis that down-regulation of aquaporins under water deprivation could be a way to minimize water loss, and the AM symbiosis could be helping the plant in this regulation.…”

“…This information would help to identify key aquaporin genes involved in the enhanced drought tolerance by the AM symbiosis. A similar approach has been followed to study aquaporins involved in stomatal gating in rice plants (Vinnakota et al, 2016). Moreover, the present work deeps on the role of aquaporins in drought tolerance and their regulation by AM fungi.…”

Form, development and function of grass stomata

“…Lastly, ZmPIP1s and ZmPIP2s are also strongly expressed in roots, indicating that these aquaporins are involved in connecting water uptake in the rhizosphere with leaf evapotranspiration. Furthermore, GC protoplasts from two drought‐tolerant rice varieties (Anna and DBN) had higher osmotic water permeability coefficients compared with a drought‐sensitive variety (ADT‐39), while in roots this trend seemed to be inverted (albeit not significantly; Vinnakota et al , ). Despite the difference in the GCs osmotic permeability no significant differences were found in the expression patterns of PIPs (PIP1 and PIP2) for ADT‐39 and Anna, while the drought‐tolerant variety (DBN) presented an increased expression of OsPIP1;1 , OsPIP1;2 , OsPIP2;1 , OsPIP2;4 and OsPIP2;5 (Vinnakota et al , ).…”

“…Furthermore, GC protoplasts from two drought‐tolerant rice varieties (Anna and DBN) had higher osmotic water permeability coefficients compared with a drought‐sensitive variety (ADT‐39), while in roots this trend seemed to be inverted (albeit not significantly; Vinnakota et al , ). Despite the difference in the GCs osmotic permeability no significant differences were found in the expression patterns of PIPs (PIP1 and PIP2) for ADT‐39 and Anna, while the drought‐tolerant variety (DBN) presented an increased expression of OsPIP1;1 , OsPIP1;2 , OsPIP2;1 , OsPIP2;4 and OsPIP2;5 (Vinnakota et al , ). The change in water permeability despite equivalent expression of aquaporins in GCs may indicate a less efficient gating capacity in the drought‐sensitive variety and thus slower stomatal aperture control (Vinnakota et al , ).…”