Abstract

The effects of 9 beta-benzoyloxy-1 alpha,2 alpha,6 beta,8 alpha,15-pentaacetoxy-dihydro-beta-agarofuran and 9 beta-furoyloxy-1 alpha,6 beta,8 alpha-triacetoxy-dihydro-beta-agarofuran, major phytogrowth inhibitors isolated from the aerial parts of Maytenus disticha (Celastraceae) and seeds of Maytenus boaria (Celastaraceae), respectively, on different photosynthetic activities of isolated spinach chloroplasts have been investigated. Photophosphorylation and electron transport (basal, phosphorylating and uncoupled) were inhibited in a concentration dependent manner by both compounds, therefore acting as Hill reaction inhibitors. The site of action of these natural compounds was located in the span from P(680) to Q(A). 9 beta-benzoyloxy-1,2,6,8,15-pentaacetoxydihydro-beta-agarofuran was one order of magnitude more potent (I(50) = 2.6 mu M) than 9 beta-furoyloxy-1,6,8,-triacetoxydihydro-beta-agarofuran, suggesting that the substitution at C-9 and the acetoxy groups at carbons 2 and 15 are important structural requirements for the displayed inhibitory activity.