Abstract
Aims: Cabraleadiol (1), Ocotilone (2) and Odoratone (3) are three triterpenes isolated from Cabralea canjerana (Vell.) Mart. (Meliaceae). They were chemically characterized, and their effect was tested on the light reaction of photosynthesis. Study Design: Natural products were used as models to find new models for inhibitors of photosynthesis. Place and Duration of Study: Departmento de Química, Universidade Federal de São Carlos and Departmento de Bioquímica, Facultad de Química, Universidad Nacional Autonoma de México, between May 2013 and January 2014. Methodology: The natural products had their effect on the light reaction of photosynthesis studied by pollarography and Chlorophyll a (Chl a) fluorescence transients. Results: The compounds inhibited ATP synthesis and electron transport rate (basal, phosphorylating and uncoupled). Therefore, they act as Hill reactions inhibitors. Their inhibition site were located in the range of electron flow from OEC complex and between P680 to QA of PS II, and inhibited the photosystem II (PS II) by inducing the appearance of a K-band which is an indicative that the photochemical apparatus is failing at the donor side of PS II interacting at the OEC complex and by transforming active reaction centers to “heat sinks” or the formation of silent reaction centers unable to reduce QA. Conclusion: Furthermore, these triterpenes inhibit PS II and induce the appearance of small G band which is related with the decreased plastoquinone (PQ) pool reduction.
Highlights
We report here the effect of cabraleadiol (1), ocotillone (2) and odoratone (3) (Figure 1), on several photosynthetic activities to help us to elucidate their mechanism of actions in isolated spinach chloroplasts, measured with polarographic techniques and fluorescence induction curves of chlorophyll a (Chl a) of Photosystem II (PS II)
To monitor Chlorophyll a (Chl a) fluorescence transients, aliquots of dark adapted thylakoids were placed by gravity on filter paper with a dot-blot apparatus (Bio-Rad, United States) to ensure a homogeneous and reproducible distribution of thylakoids in the filter paper, the filter paper were dipped immediately in 3 mL of electron transport medium with 200 and 800 μM of the tested compound, the reaction medium used was as the same employed in basal non-cyclic electron transport measurements
ATP Synthesis To know if the triterpenes 1 - 3 inhibit ATP synthesis, all of them were assayed on photophosphorylation activity coupled to electron transport from water to MV in isolated freshly lysed spinach chloroplasts
Summary
Three natural triterpenes (1 - 3) were isolated from the ethanol extracts of the seeds and fruits of Cabralea canjerana (Vell.) Mart. (Meliaceae) as previously has been published [15]-[20]. Three natural triterpenes (1 - 3) were isolated from the ethanol extracts of the seeds and fruits of Cabralea canjerana (Vell.) Mart. (Meliaceae) as previously has been published [15]-[20]. Stock solutions for compounds 1 - 3 were prepared using a DMSO
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