Fate of the Liberated Amino Acids

The conversion of aspartate to homoserine occurs first within the cotyledons, and then the homoserine is transported to the roots and the shoot (Fig. 6.19). Very little aspartate or glutamate is transported to the axis, so in pea, unlike in cereals and castor bean, these are not the major transport forms of amino acids this role is attributed to homoserine. Homoserine itself is utilized only slowly in etiolated peas, for when C-homoserine is injected into cotyledons only 6% is respired over the subsequent ten days while 80% remains unchanged. At this time there is an almost equal distribution of this unmodified homoserine between the cotyledons and the growing axis [84]. 

Similarities between the mechanisms by which the products of proteolysis of the endosperms of castor bean and of maize are processed and transported are evident. The involvement of homoserine may be peculiar to mobilization from the cotyledons of Pisum (or perhaps legumes) since little or no homoserine has been reported in other plants, and the full significance of this interesting digression from the norm is not yet understood. 

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