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Effect of some heterocyclic herbicides on CO 2 assimilation by spinach chloroplasts
Author(s) -
DÍAZ MARÍA A.,
CHUECA ANA,
GORGÉ JULIO L.
Publication year - 1980
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1980.tb02650.x
Subject(s) - simazine , ribulose , paraquat , chemistry , photosynthesis , spinacia , spinach , biochemistry , chloroplast , rubisco , ribitol , enzyme , atrazine , biology , pesticide , gene , agronomy
We have studied the inhibitory effect of heterocyclic herbicides simazine, paraquat, pyrazon and amitrole on photosynthetic CO 2 fixation and on the level of intermediates of the CO 2 assimilation cycle in isolated spinach ( Spinacia oleracea ) chloroplasts, as well as their in vitro activities on ribulose‐1,5‐bisphosphate carboxylase and fructose‐1,6‐bisphosphatase. The half inhibitory concentrations (I 50 ) of CO 2 assimilation were about 1 μ M for simazine and paraquat, and 10 μ M for pyrazon. Amitrole, with an I 50 100 μ M , gave only a weak inhibition. In the presence of simazine or pyrazon the triose‐phosphates/phosphoglycerate ratio diminished because of a decrease of the triose‐phosphates percentage from 47% to 19%, which means an inhibition of the phosphoglycerate reduction step by a low NADPH synthesis. However, there was not a parallel increase of phosphoglycerate, because of collateral pathways leading to phospho‐enolpyruvate, amino acids and other non‐identified compounds. Paraquat did not give such a decreased ratio, which could be explained as an inhibition of some step of the Calvin cycle later than triose‐phosphates by the H 2 O 2 formed in a Mehler reaction. Amitrole did not show any effect on the pattern of intermediates. Simazine and pyrazon at 10 μ M concentration promote a 20–30% activation of ribulose‐1,5‐bisphosphate carboxylase activity, whereas paraquat, pyrazon and simazine showed an I 50 about 100 μ M for the inhibition of the photosynthetic fructose‐1,6‐bisphosphatase.