The role of aerenchymatous gas space in root sodium ion management under salt stress: Do they matter in rice?

Abstract

Background & aims: Increasing soil salinity is an emerging and potent threat to agricultural crop production. Plant root tissues are the most important place for salt sensing. Thus, root traits associated with salt tolerance are very important. Identification of new root traits may help us to optimize plants' overall performance under stress.

Methods: An experiment was conducted with eight rice genotypes and root aerenchymatous gas space, Na+, and K+ concentrations of root and leaf were measured. A further experiment was performed with four selected rice genotypes based on morphological, physiological, biochemical, and molecular traits.

Key results: We identified root tissue porosity and root aerenchymatous gas space was increased under salt stress and the induction of these traits was greater in salt-tolerant genotypes (FL478, AC39416A, and Rashpanjor) as compared to salt-susceptible genotype (Naveen). Most interestingly, root porosity and aerenchymatous gas space showed a strong correlation with leaf Na+ ion concentration as well as leaf and root K+ ion retention. Thereby, it seems more porous roots can play an important role in Na+ transport and K+ retention in salt-tolerant rice plants. Additionally, we observe relatively higher expression of ROS-induced NADPH oxidases (OsNOX5 and OsNOX9) genes in FL478, AC39416A, and Rashpanjor as compared to Naveen, whose function is associated with programmed cell death (PCD) and lysegenous aerenchyma formation in rice.

Conclusions: Overall the findings suggest that tolerant and moderately tolerant rice genotypes followed PCD in root cortical tissues that help to restrict upward movement of Na+ and retention of K+ in rice under saline conditions.