Developmental Biochemistry of Cottonseed Embryogenesis and Germination

The composition of the free amino acid pool in embryonic cotton (Gossypium hirsutum) cotyledons is quite distinct from that of endosperm, and that of germinated, greened cotyledons is quite distinct from that of leaves. During germination (including the precocious germination of immature seeds), the pool expands considerably showing a pronounced accumulation of asparagine. The high level of asparagine found in seedling roots and in the cotyledon vascular exudate indicates that this is the major transported amino acid in germination. There is no pool expansion in the presence of abscisic acid. In the presence of actinomycin D, the pool expands, but an enormous accumulation of glutamine takes place. The composition of the pool at any stage is not related to the composition of the isoacceptor transfer RNA pool, nor to the composition of the storage protein. Anaerobiosis leads to an accumulation of aspartate, alanine, and glycine at the expense of asparagine; however, desiccation does not result in an accumulation of proline. Conspicuously high levels of arginine are maintained through embryogenesis and germination. The levels of individual amino acids are presented as nanomol per cotyledon pair and as per cent of total pool.