The 8th international symposium on the plant hormone ethylene edition:8 location:Cornell University, Ithaca, New York, USA date:21-25 June 2009
S-adenosyl-L-methionine (SAM) plays an important role in both eukaryotic and prokaryotic cells. It is the main methyl-donor in all living organs and it is involved in polyamine biosynthesis. In plants, SAM is also a substrate for the production of ethylene. SAM is converted to ACC (1-aminocyclopropane-1-carboxylic acid) by ACC-synthase (ACS) with the cleavage of 5’-methylthioadenosine. The role of SAM during climacteric ripening, besides being a substrate for ACS, is not yet fully elaborated on. SAM has not yet been quantified in fruit tissue in relation to climacteric ripening and other processes like e.g. methylation activity.
Our current research project aims to develop a kinetic model that describes ethylene production during climacteric ripening of tomato. Within this framework we collect systematic quantitative data on the ethylene biosynthesis pathway. To routinely quantify SAM in tomato tissue we developed a capillary electrophoresis technique. Our results surprisingly show that the SAM-pool is not constant during tomato fruit development and ripening. Initially, the SAM content is high (8.5 ± 1.7 nmol/g FW) measured shortly after anthesis and decreases as the fruit further develops. SAM-content is more or less constant (5.9 ± 0.6 nmol/g FW) when the fruit is fully developed but still preclimacteric. At the onset of climacteric ripening, SAM content increases and exceeds preclimacteric values (up to 10.6 ± 0.9 nmol/g FW). During post-harvest storage, SAM content will decrease again (until 4.7 ± 0.6 nmol/g FW). The SAM-profile matches exactly the ethylene production profile. These results suggest that SAM content is regulated during fruit development, climacteric ripening and postharvest storage. Further research is needed to elaborate on the underlying control mechanism. Is there an increased SAM synthesis, or a reduced SAM uptake by other pathways, during climacteric ripening of tomato?