An analysis of the inhibitory effects of linolenic acid upon photosystem II of higher plants

• Main Author: Iven, Mark Edward
• Format: Others
• Published: PDXScholar 1989
• Subjects: Linolenic acid; Photosynthesis; Environmental Chemistry
• Online Access: https://pdxscholar.library.pdx.edu/open_access_etds/3893; https://pdxscholar.library.pdx.edu/cgi/viewcontent.cgi?article=4888&context=open_access_etds

This study utilizes steady state fluorescence measurements, flash-induced P680+ absorption transients, and DCIP reduction kinetics to study the inhibitory effects of linolenic acid (LA) upon Photosystem II (PSII) in whole spinach chloroplasts and insideout wheat thylakoids. It confirms the presence within PSII of LA-induced inhibition of energy trapping and/or primary charge separation (i.e., primary inhibition), in addition to donor side inhibition. The latter is diminished in the presence of 1,5-Diphenylcarbohydrazide (DPC) and probably takes place at the oxygen evolving complex. Primary inhibition, which is more controversial, probably occurs between Ph and QA, with a likely contribution at the level of PSII energy trapping. In addition, the ability of Mg2+ to delay a drop in steady state fluorescence intensity normally associated with thylakoid exposure to LA is explained by the ability of this cation to confer resistance to LA-induced destacking of thylakoid membranes. Steady state fluorescence results in the presence of DCMU, dithionite and LA also support the presence of an additional acceptor between Ph and QA. This acceptor, designated here as "R." is proposed not to be a sequential member of the transport chain, but may be accessible to it via QA when the chain blocked, such as with DCMU.R- is proposed to exert a coulombic effect upon Ph, thereby affecting the degree of primary charge recombination. It may be related to one of the several acceptors already proposed by others and the need for more study is stressed in order to confirm or refute its existence.