The regulation of ethylene biosynthesis by the ethylene-forming enzyme in plant tissues.
Porter, A. J. R.
Dissertation Abstracts International. B, Sciences and Engineering Year: 1991 Vol: 52 Issue: 3 Pages: 1171B
1991
บทคัดย่อ
Activity of the ethylene forming-enzyme (EFE) was characterized in a variety of plant tissues, both in vivo and in vitro. In hypocotyl segments of mung beans and in discs of beetroots, EFE activity was determined at the same time as the plasma membrane potential difference, measured with a microelectrode, was progressively reduced by titration with protonophores and with KCl. The results obtained were not consistent with the proposal that an electric potential-dependent EFE activity is located on the plasma membrane of plant cells. Activity of the ethylene forming enzyme was compared in leaf discs, isolated cells, protoplasts and vacuoles derived from leaves of peas and Vicia faba. Some 95% of the activity observed with leaf tissue was lost when cells were isolated from the tissue. The limited activity observed with the isolated cells was largely retained by protoplasts and vacuoles isolated from the protoplasts, but was lost when the vacuoles were lysed. Isolation of cells by gentle disruption of cladophylls from Asparagus sprengeri [A. densiflorus] or leaves from mung beans resulted in a loss of about 80% and 70% of EFE activity, respectively. It was proposed that full EFE activity in vivo requires tissue integrity in addition to a previously noted requirement for membrane integrity. The EFE activity of kiwifruit membranes showed characteristics of the enzyme in vivo, in its stereoselectivity towards isomers of 1-amino-2-ethylcyclopropanecarboxylic acid, its pattern of development during postharvest ripening and its sensitivity towards inhibitors. This demonstration of authentic EFE activity in vitro provided a useful system for studying EFE activity in plant tissues.