CYTOKININ AFFECTS NUCLEAR-ENCODED AND PLASTOME-ENCODED ENERGY-CONVERTING PLASTID ENZYMES

Cytokinins induce two specific morphological alterations in mosses: (i ) the differentiation of a tip-growing cell into a three-faced apical cell (the so-called bud), and (ii) the division of chloroplasts. In a developmental mutant of the moss Physcomitrella patens (Hedw.) B.S.G. (mutant PC22) impeded in both cellular differentiation (bud production ) and chloroplast division, addition of cytokinin (N-6-Delta(2)-isopen tenyladenine) led to bud production after 3 d in the wild type and aft er 7 d in the mutant. Hormone induced a division of the mutant macroch loroplasts starting within 24 h and ongoing for 72 h. During this peri od the abundances of several plastid proteins changed in both genotype s as judged by two-dimensional-protein gel electrophoresis, silver sta ining and subsequent quantification with novel computer software. Eigh t of these polypeptides were isolated independently, subjected to micr osequencing and thus identified, resulting in the first protein sequen ce data from a moss. Three polypeptides (24 kDa, 22 kDa, 20 kDa) were found to be homologous to enhancer protein OEE2 of the oxygen-evolving complex, four to represent isoforms of phosphoglycerate kinase (EC 2. 7.2.3), and one was identified as the beta-chain of chloroplast ATPase (EC 3.6.1.34). Possible involvement of these key enzymes of the chlor oplast energy-conversion machinery in organelle division and in cellul ar differentiation is discussed. Further sequence information was obta ined from both subunits of ribulose-1,5-bisphosphate carboxylase/oxyge nase (EC 4.1.139). Amounts of these polypeptides were not appreciably affected by cytokinin in moss chloroplasts.