Ribonuclease and Other Factors Involved in the Respiratory Senescence of Maize Scutellum

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Abstract
The scutella from seedlings of Zea mays L. germinated at 28–30° C increase in respiration rate to the third day, followed by a decline which is quite noticeable by the fifth day. A search has been made for factors responsible for the respiratory decline. The electronmicroscope shows the five-day mitochondria to be normal in appearance. Very active preparations are obtained by isolating the mitochondria at pH 7.6 with inclusions of bovine serum albumin and ethylenediamine-tetraacetic acid. A soluble ribonuclease (RNase A) which increases rapidly with age impairs both oxidation and phosphorylation. The largely particle-bound ribonuclease (RNase B) is not inhibitory. Plant ribonuclease is resistant to the proteolysis occurring during senescence. It is suggested that the soluble ribonuclease contributes to the respiratory decline, but that other factors may also be involved.