Growth and mitochondrial respiration of mungbeans (Phaseolus aureus Roxb.) germinated at low pressure

Mungbean ( Phaseolus aureus Roxb.) seedlings were grown hypobarically to assess the effects of low pressure (21-24 kilopascals) on growth and mitochondrial respiration. Control seedlings grown at ambient pressure (101 kilopascals) were provided amounts of O 2 equivalent to those provided experimental seedlings at reduced pressure to factor out responses to O 2 concentration and to total pressure. Respiration was assayed using washed mitochondria, and was found to respond only to O 2 concentration. Regardless of total pressure, seedlings grown at 2 millimoles O 2 per liter had higher state 3 respiration rates and decreased percentages of alternative respiration compared to ambient (8.4 millimoles O 2 per liter) controls. In contrast, seedling growth responded to total pressure but not to O 2 concentration. Seedlings were significantly larger when grown under low pressure. While low O 2 (2 millimoles O 2 per liter) diminished growth at ambient pressure, growth at low pressure in the same oxygen concentration was enhanced. Respiratory development and growth of mungbean seedlings under low pressure is unimpaired whether oxygen or air is used as the chamber gas, and further, low pressure can improve growth under conditions of poor aeration.