We present two pieces of evidence that regulation of cytoplasmic pH near neutrality is a prerequisite for survival of root tips during hypoxia. First, blackeye peas and navy beans show earlier cytoplasmic acidosis under hypoxia than soybeans or pumpkin or maize, and die earlier. Second, when cytoplasmic acidosis in maize root tips is greatly retarded by treatment with 25 millimolar Ca(NO3)2, they remain viable under hypoxia for a much longer period of time than untreated hypoxic root tips. We also show that viability of maize root tips is unaffected by the supply of exogenous sugar (and so on the rate of ethanolic fermentation) for at least 16 hours of hypoxia.
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