|Author: ||A. H. Halevy|
Detailed ultrastructural studies during petal senescence were carried out by Matile's group on Ipomoea tricolor.
The first noticeable sign of aging was invagination of the tonoplast indicating autophagic activity in the vacuole.
This concept was challenged by some workers on the basis of direct analysis of isolated petal vacuoles.
One of the most obvious symptoms of the final stage of senescence in petals is the loss of water even when the flowers are held in water.
This may indicate a loss of membrane integrity, causing increased permeability and leakage.
Direct measurements of biochemical and biophysical properties of petal membranes during development and aging have been carried out recently in our laboratory by A. Borochov, M. Shinitzki, J. Thompson and S. Mayak.
A sharp increase in microviscosity of the rose plasmalemma and of carnation microsomal membranes was observed during aging.
This change was found in protoplasts isolated from intact flowers, cut flowers and isolated petals.
It was related to external conditions affecting the rate of senescence, such as temperature, pH and ethylene.
The increase in microviscosity corresponded to an increase in the ratio of free sterol to phospholipid.
No change in the content of free sterol occurred during senescence, but phospholipid content was reduced.
This was attributed both to reduced synthesis and increased hydrolysis by phospholipase A.
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