Potentially defensive proteins in mature seeds of 59 species of tropical leguminosae.

A survey of 59 species of tropical legume seeds revealed high interspecific variation in proteinaceous capacity to inhibit bovine trypsin (a digestive enzyme) and to agglutinate human (type B, Rh positive) and laboratory rabbit red blood cells. The legume subfamily Mimosoideae was conspicuous for the absence of seeds with very weak trypsin inhibition. Congenerics sometimes differed strongly from each other with respect to both trypsin inhibition and phytohemagglutination. Half the species of seeds displayed no hemagglutinating capacity with one or the other kinds of red blood cells, and in only 27% of the 30 cases where there was some activity did the same species of seed actively agglutinate both species of red blood cells. A species of seed that had hemagglutinating capacity was almost invariably associated with moderate to high levels of trypsin inactivation. While it has been long known that a great diversity of small toxic and potentially defensive molecules occur in legume seeds and that one species of seed often contains several of them, we now feel that it is reasonable to consider legume seeds as also containing a high diversity of potentially toxic protein molecules. A single seed is likely to contain, at the least, three to four classes of defensive compounds, any or all of which, or some in combination, may be the cause of a seed being rejected by a potential seed predator.