Cytokinin metabolism and cytokinin oxidase and adenine phosphoribosyltransferase activity in male sterile Brassica napus leaves

Abstract

The metabolism of [ 14C]zeatin (Z) and [ 3H]dihydrozeatin (DZ), and the activity of two key enzymes in cytokinin (CK) metabolism, i.e. CK oxidase and adenine phosphoribosyltransferase (APRT), was studied in the leaves of wild type (WT) and genic male sterile (GMS) plants of Brassica napus. The leaves of the GMS plants metabolized Z and DZ less efficiently compared to WT leaves. Adenine (Ade) was the major metabolite of Z in both the leaves, and GMS leaves produced 50% less Ade in comparison with WT leaves. This correlated well with the CK oxidase activity in the two types of leaves; WT leaves show twice the activity of this enzyme in comparison with GMS leaves. GMS leaves produced higher amounts of DZ nucleotide than the WT leaves, and this correlated with 17% more APRT activity in GMS leaves. There was no difference in the amount of Z nucleotide produced by the two types of leaves. The results presented show that mutation in a gene controlling male fertility affects CK metabolism in vegetative tissues, in addition to reproductive tissues (reported earlier), and is related to the activity of at least two enzymes involved in CK metabolism.