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PHOTOSENSITIZED INHIBITION OF PHOTOSYNTHETIC 14 CO 2 FIXATION BY α‐TERTHIENYL AND ULTRAVIOLET‐A *
Author(s) -
Brennan Thomas M.
Publication year - 1994
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1994.tb09668.x
Subject(s) - chloroplast , photosynthesis , hill reaction , chemistry , biochemistry , photosystem i , thylakoid , malate dehydrogenase , chlorophyll , succinate dehydrogenase , biophysics , photosystem ii , botany , biology , enzyme , gene
A variety of naturally occurring photosensitizers of plant origin were tested for their ability to cause ultraviolet‐A (UVA)‐dependent inhibition of photosynthetic 14 CO 2 fixation in leaf disks of Pisum sativum L. At 0.1 m M concentrations and 60 min UVA irradiation, α‐terthienyl was strongly inhibitory, harmine and sanguinarine inhibited to a lesser degree, and curcumin, 8‐methoxypsoralen and nordihydroguaiaretic acid had no effect under the conditions tested. Alpha‐terthienyl + UVA treatments that fully inhibited 14 CO 2 fixation had no effect on fresh weight, chlorophyll or protein content of the tissue. Chloroplast malate dehydrogenase and glyceraldehyde‐3‐phosphate dehydrogenase were inhibited 45% and 29%, respectively, by α‐terthienyl + UVA treatment. Electron transport from H 2 O to the reducing side of photosystem I was inhibited to a similar extent, suggesting interference with the reductive activation of chloroplast enzymes. Alpha‐terthienyl + UVA‐treated tissue exhibited a seven‐fold increase in leakage of labeled photosynthate into the external medium. Treated leaf disks showed no ability to recover 14 CO 2 fixing ability over a 24 h period. These results indicate photosensitized damage at the level of the thylakoid membranes resulting in partial loss of electron transport capability and more general damage to chloroplast and cell membranes.