Abstract
Oxygen depletion under waterlogged conditions results in a compromised operation of H+-ATPase, with strong implications for membrane potential maintenance, cytosolic pH homeostasis, and transport of all nutrients across membranes. The above effects, however, are highly tissue specific and time dependent, and the causal link between hypoxia-induced changes to the cell's ionome and plant adaptive responses to hypoxia is not well established. This work aimed to fill this gap and investigate the effects of oxygen deprivation on K+ signalling and homeostasis in plants, and potential roles of GORK (depolarization-activated outward-rectifying potassium) channels in adaptation to oxygen-deprived conditions in barley. A significant K+ loss was observed in roots exposed to hypoxic conditions; this loss correlated with the cell's viability. Stress-induced K+ loss was stronger in the root apex immediately after stress onset, but became more pronounced in the root base as the stress progressed. The amount of K+ in shoots of plants grown in waterlogged soil correlated strongly with K+ flux under hypoxia measured in laboratory experiments. Hypoxia induced membrane depolarization; the severity of this depolarization was less pronounced in the tolerant group of cultivars. The expression of GORK was down-regulated by 1.5-fold in mature root but it was up-regulated by 10-fold in the apex after 48 h hypoxia stress. Taken together, our results suggest that the GORK channel plays a central role in K+ retention and signalling under hypoxia stress, and measuring hypoxia-induced K+ fluxes from the mature root zone may be used as a physiological marker to select waterlogging-tolerant varieties in breeding programmes.
Highlights
Waterlogging (WL) is a major environmental constraint limiting agricultural production worldwide and hampering 10% of the global land area (Setter and Waters, 2003)
The results showed that WL treatment induced the chlorosis and necrosis of leaves, and the tolerant cultivars performed much better as compared with the sensitive cultivars (Fig. 1D)
Potassium plays an important role in plant adaptive responses to the hostile
Summary
Waterlogging (WL) is a major environmental constraint limiting agricultural production worldwide and hampering 10% of the global land area (Setter and Waters, 2003). Drops down rapidly from 230 nmol m−3 (well-drained soil) to 50 nmol m−3 (hypoxic) (Turner and Patrick, 1968) or may even result in a complete absence of oxygen (anoxia), due to high microbial activities (Ponnamperuma, 1984). Under these hypoxic and anoxic conditions, the resultant O2 deficiency and accumulation of CO2 in the root zone limit the root metabolism, aerobic respiration, and ATP synthesis, affecting the growth of shoots and roots (Gibbs and Greenway, 2003; Bailey-Serres and Colmer, 2014). Hypoxia limits the availability of required energy to fuel the H+ATPase pumps and severely affects the transportation of ions which affect the growth and yield (Bailey-Serres and Voesenek, 2008; Elzenga and van Veen, 2010)
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