The behavior of cytoplasmic membranes in Phaseolus vulgaris cotyledons during germination

Abstract

Information about the effects of germination on cytoplasmic membranes of cotyledons has been obtained by examining selected properties of smooth microsomes purified from cotyledon tissue at various stages of germination. The microsomal membranes contained rotenone-insensitive NADH – cytochrome c reductase (EC. 1.6.99.3) and NADPH – cytochrome c reductase (EC. 1.6.99.1). Measurements of these enzymes in smooth microsomal fractions isolated from various ages of cotyledon tissue revealed that their activities markedly decrease during the late stages of germination, coincident with onset of cotyledon senescence. This decrease is closely paralleled by a corresponding decline in total levels of the enzymes in the cotyledons during the same period, and has been interpreted as reflecting deterioration of cytoplasmic membrane structure and function concurrent with the progression of senescence. The membrane-bound cytochrome c reductase activity does not appear to be solubilized as a result of this deterioration. Furthermore, the protein:phospholipid ratios for the smooth microsomal preparations remain essentially unchanged during germination. This suggests that the macro-molecular complexes of membranes disaggregate more or less spontaneously during senescence and that in the process, the cytochrome c reductases are inactivated.