Amino acid-activating enzymes in germinating pea seedlings

Abstract

The properties and distribution of the amino acid-activating enzymes in young pea plants have been investigated. In leaves, the major activity was in the soluble fraction of chloroplasts and in the supernatant fraction of intact tissue homogenates. In embryonic root tissue most activity was in the microsomal and supernatant fractions. The increased activity of these enzymes during germination is largely due to de novo synthesis rather than activation. Simazine, Atrazine, Diquat, 2,6-dichlorobenzonitrile, chloramphenicol, p-fluorophenylalanine and gibberellic acid had no effect on the activity of partly purified systems. Ribonuclease appeared to render the enzyme less precipitable at pH 5· rather than to inhibit the enzymatic reaction. A short exposure to red light stimulated equally growth and activity of the amino-acid-activating system in etiolated seedlings; the effect was nullified by subsequent exposure to far-red light. If seedlings were treated with red light 1 hr before being brought into the light then no significant effect on the enzyme system could be observed.