Adenylate Kinase in Tobacco Cell Cultures. II. Variability and Regulation of Isoform Activity Patterns in Different Cell Lines

Abstract

Summary Specific activity and isoform patterns of adenylate kinase (AK) were investigated in tissue cultures of cloned tobacco cell lines that differed mainly in hormone requirement, proximate cause of hormoneautotrophy and neoplastic growth characteristics. Variations in the AK isoform pattern were related to growth and ageing processes, differentiation state of tissues, differences between culture cycles as well as the neoplastic characteristics of the cell lines. High specific AK activity and isoform patterns with dominating chloroplastic activities appeared as typical of green, photosynthetic and actively growing tissues (calli in growth phase, callus outer tissues). Lower specific AK activity and isoform patterns with dominating cytosolic activity were typical for senescent or non-photosynthetic tissue (calli in stationary phase, callus core tissues), but sometimes also occurred in entire young calli, apparently as a consequence of stress. This isoform pattern is therefore proposed as a stress marker in plant cell cultures. The isoform patterns of the different cell lines were analyzed in detail for the variations during different culture cycles and the differences appearing under optimal growth conditions. The observed characteristics were related to proximate cause of hormone-autotrophy and neoplastic state. The main differences appeared between normal and neoplastic, transformed tissues. Changes in compartmentation of AK activities under different metabolic situations are discussed with respect to the physiological characteristics of the cell lines, energy metabolism and ATP/ADP ratios of cellular compartments and the presumed role of AK in ageing and stress.