Revealing the roles of GORK and NADPH oxidase in adaptive response to hypoxia and salinity stress and their combination in Arabidopsis

F Wang1, Z Chen2, T Colmer3, L Shabala1 and S Shabala1

  1. School of Land and Food, University of Tasmania, Hobart, Tasmania 7001, Australia
  2. School of Science and Health, Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW 2751, Australia
  3. School of Plant Biology and Institute of Agriculture, The University of Western Australia, Crawley, WA 6009, Australia

The potential roles of GORK and RBOHD transporters in plant adaptive responses to separate or combined hypoxia and salinity stress were investigated in the context of tissue specificity (epidermis vs stele; elongation vs mature zone) in Arabidopsis. The expression of GORK and RBOHD was significantly decreased in WT root after onset of hypoxia. A loss of GORK displayed a waterlogging-tolerant phenotype while rbohD knockout was sensitive to waterlogging. To understand their functions under separate or combined hypoxia and salinity stress, we studied K+, Ca2+, Na+ distribution in root different tissues and zones using fluorescence imaging dyes. gork1-1 plants had better K+ retention ability in both elongation and mature zone compared with WT and rbohD under both hypoxia and salinity. We also found 72 h of hypoxia induced Ca2+ increase in each zone and tissue, and the increase was much less pronounced in rbohD than in WT. In most tissues except elongation zone in rbohD, H2O2 concentration has decreased after 1 h of hypoxia, but then increased significantly after 24 h of hypoxia in each zone and tissue, further suggesting that RBOHD may shape stress-specific cytosolic Ca2+ signatures via modulation of apoplastic H2O2 production. The adverse effects of combined stress were much stronger in the mature zone with relatively lower cell viability compared with other zones in three genotypes. Taken together, our data suggest plants lacking functional GORK channel are capable to better retain K+ which benefits their performance under separate or combined hypoxia and salinity stress, and RBOHD plays a key role in hypoxia-induced Ca2+ signalling thus composing an important part of stress sensing and acclimation mechanism.