³¹P-NMR study of the physiological conditions in intact root cells of mung bean seedlings under low-temperature stress

Intracellular pH and levels of ATP in intact root-tip cells of mung bean (Vigna mungo [L.] Hepper) under low-temperature stress were investigated in vivo by ³¹P nuclear magnetic resonance (³¹P-NMR) spectroscopy. Root-tips of 3 mm in length were excised from seedlings of mung bean that had been chilled at 0°C after grown at 30°C. Chilling for longer than 12 h caused changes in the intracellular pH and decreased levels of ATP in the seedlings. The level of ATP recovered within 30 min but little change in pH was observed when samples were rewarmed to 20° C after chilling at 5°C. However, after chilling for longer than 48 h, neither the intracellular pH nor the level of ATP was restored.These results suggest that a decline in the activity of tonoplast H⁺-ATPase, induced by chillings, might be a significant early event in cold-induced injury that leads to cell damage.