Acg. Horta et L. Sodek, FREE AMINO-ACID AND STORAGE PROTEIN-COMPOSITION OF SOYBEAN FRUIT EXPLANTS AND ISOLATED COTYLEDONS CULTURED WITH AND WITHOUT METHIONINE, Annals of botany, 79(5), 1997, pp. 547-552
The in vitro culture of immature soybean cotyledons (in direct contact
with the medium) and immature fruit explants (stem dipping into the m
edium) on a defined medium containing glutamine and sulphate as sole s
ources of N and S for 7 d led to rates of growth and reserve protein a
ccumulation close to, or greater than, those occurring in situ. Supple
mentation of the medium with 8.4 mM methionine had little effect on gr
owth and protein accumulation. of the cotyledons in the explant system
, but did result in significant increases in the isolated cotyledon sy
stem. Methionine suppressed the synthesis of the 7S beta-subunit in bo
th systems. The free amino pool of the cotyledons increased more than
three-fold when methionine was present in the explant medium. In the i
solated cotyledon system, the basal medium alone caused a large increa
se (over 30-fold) in the free amino acid fraction, but methionine resu
lted in an even greater increase (over 50-fold). In both systems the e
xpansion involved a very large increase in the methionine pool, but ma
ny other amino acids also showed large increases. Specific effects of
methionine on individual amino acids were more clear in the explant sy
stem, where its presence resulted in marked increases in serine, alani
ne and asparagine. The data show that an abnormal situation arises on
feeding with methionine, a fact to be considered before attributing ef
fects on growth and protein synthesis directly to methionine. (C) 1997
Annals of Botany Company.