CYTOKININ CONJUGATION - RECENT ADVANCES AND PATTERNS IN PLANT EVOLUTION

Cytokinin (CK) conjugates are important in plant development because t hey regulate active CK concentrations, CK transport, storage, and irre versible inactivation. While numerous CK conjugates have been identifi ed in higher plants, the biological functions of these compounds, thei r location within cells and tissues, and the enzymes and genes involve d in their regulation are not clearly understood. In this paper, recen t advances are reported which have occurred through the study of trans genic plants containing the ipt or rolC genes, the identification of n ew regulatory enzymes affecting CKs, and the characterization of new C K conjugates. In addition, a survey of the literature is presented whi ch examines the pattern of CK conjugates found in different plant taxa . Based on current knowledge, it appears that green algae, mosses, and ferns contain relatively few CK conjugates of isopentenyl adenine (iP ) and zeatin (Z). In contrast, higher land plants, such as gymnosperms and angiosperms, contain a more complex set of CKs, primarily conjuga tes of Z and dihydrozeatin (DHZ). This suggests that the pattern of CK conjugation has become more complex in parallel with the increasing c omplexity of higher plants.