Effects of Anoxia on Solute Loss from Beetroot Storage Tissue

Beetroot storage tissue that had been aged in an aerated solution was particularly suited for studies of solute losses duringanoxia; retention of betacyanin being a good indicator of tonoplast integrity. During anoxia, loss of K+ was nearly always greater than that of Na+ while Cl– loss was intermediate. Supply of glucoseduring ageing increased the tolerance of beetroot tissue to anoxia. In these tolerant tissues, there were three phases of solute loss.During the first phase, losses of K+ and amino acids were rapid, presumably due to membrane depolarization from –156 to –95 mV. In contrast, losses of Na+ and Cl– were slow. During the second phase, K+ loss had decreased to a low rate, while losses of Na+ and Cl+ remained slow. Furthermore, the membrane potential remained at –95 to –90mV, which was consistent with the diffusion potential estimated from the modified Goldman equation. In the third and final phase, loss of K+ Na+ Cl+,sugars, and amino acids began to increase, soon followed by loss of betacyanin. Tissues that had lost their betacyanin during anoxia were irreversibly injured, as shown by rapid uptake of Evans Blue and afailure to take up K+ , Na+ and Cl+ during re–aeration. In contrast, tissues which had retained their betacyanin did not take upEvans Blue, but took up substantial amounts of K+ , Na+ , and Cl– after re–aeration. After return to air for 1.5 h, tissue that hadretained its betacyanin had a membrane potential of – 154 mV.