AGE-RELATED-CHANGES IN BIOCHEMICAL AND PHYSICAL-PROPERTIES OF CARNATION PETAL PLASMA-MEMBRANES

Senescence of flower petals, as of other plant organs, is accompanied by numerous well-defined compositional, structural and functional changes in their cellular membranes. The aim of this work was to compare the modifications occurring in the bulk of the cellular membranes, the microsomal fraction, to those occurring in a purified plasma membrane preparation. Microsomal membranes were prepared from petals of carnation (Dianthus caryophyllus L., cv. White Sim) using differential centrifugation, and plasma membranes were isolated from this fraction using two-phase partition. Of the various membrane marker enzymes tested, vanadate-sensitive ATPase showed the most pronounced decline with age. Proteins and phospholipids declined in both microsomal and plasma membranes. In contrast, free sterol content did not change with age in microsomal membranes but declined in plasma membranes. Membrane lipid fluidity, assessed through fluorescence polarization of 1,6-diphenyl hexatriene, was lower in plasma membranes and decreased with age in both membrane preparations. The binding of GTP to microsomal membranes declined significantly with age. In contrast, binding of GTP to plasma membranes was similar to GTP binding to microsomal membranes from young petals and did not change with age. Use of the thiol specific fluorescent probe, N-dansylaziridine, showed that membrane protein thiols declined quantitatively with age in both microsomal and plasma membranes. However, while the two preparations differed with respect to the labeling rates, the similar fluorescence spectra of the labeled preparations suggests that the polarities of the protein thiols in the two membrane types are comparable. We conclude that microsomal membranes may represent the petal plasma membranes in senescence-related studies of most properties, but not in that of GTP binding or kinetics of protein thiol labeling.