Effects of Anoxia on Uptake and Loss of Solutes in Roots of Wheat

Abstract

This paper reports on leakage of K+, Cl-, free amino acids and soluble sugars from roots of 4-5-day-old intact wheat seedlings, exposed to anoxia. Leakages were slower from hypoxically than from aerobically pretreated roots. For the first 24 h of anoxia, leakage of K+ and free amino acids was similar, while sugar leakage was slow. Subsequently, leakage of all three solutes usually increased with time. Net losses of K+ and Cl-, after 48 or 72 h exposure of intact seedlings to anoxia, were faster, and/or occurred earlier: (i) in expanding than in expanded root tissues; (ii) at 25� than at 15�C. Re-aeration showed that expanded root tissues retained their capacity to take up K+ and accumulate Cl-, for at least 12 h after the root tips had lost their ability to elongate. Roots which had lost their elongation potential after 20 h of anoxia, as diagnosed by microscopic observation, still had high solute concentrations in the 1-5 mm and 10-20 mm segments from the root tip, but the 0-1 mm apices had lost 70-90% of their K+, free amino acids and soluble sugars. In contrast, solute concentrations were still high in 0-1 mm tips which had not yet lost their elongation potential. Thus, either irreversible injury of the apices is caused by sudden loss of membrane integrity, or there is another cause of death leading to rapid leakage.