Effects of a 4-deoxyphorbol triester from the latex sap of Euphorbia biglandulosa Desf. on isolated spinach chloroplasts

Abstract

The effects of a 4-deoxyphorbol triester (4-DPT) extracted from the latex sap of Euphorbia biglandulosa Desf. on isolated intact chloroplasts and thylakoid membranes from spinach leaves ( Spinacia oleracea L. cvs. Monatol) have been investigated. Light-induced electron flow through photosystem II was highly sensitive towards the diterpene ester: half-maximal inhibition of ferricyanide reduction was obtained with 4 to 7 × 10 −7 moles 4-DPT/mg chlorophyll. In contrast, the ADP/2e - ratio of noncyclic photophosphorylation which accompanies K 3[Fe(CN) 6] reduction remained nearly unaffected. At concentrations of 4-DPT which caused half-maximal inhibition of ferricyanide reduction, neither drastic changes in photosystem I-dependent photochemical reactions nor alterations in the permeability characteristics of the chloroplast envelope were observed. However, 4-DPT to some extent affects the permeability of the thylakoid membranes. From the data it can be concluded that 4-DPT, which has a strong inhibitory activity on rat liver mitochondria, also acts as a highly effective inhibitor of photosynthetic electron transport.