Phenolic Synthesis in Relation to Chloroplast Ultrastructure in Flax Callus and Cell Suspension Cultures

Abstract

Summary The distribution of phenolic compounds, chlorophyll content and enzymes of phenolic synthesis were studied in relation to the ultrastructure of chloroplasts in cotyledons, callus tissue and cell suspension cultures of the oil flax (Linum usitatissimum L.). Significant biochemical changes were observed in the cultured tissues as compared with the intact cotyledons which involved: (a) a marked decrease in the amounts of p-coumaric, caffeic and ferulic acids, as well as the chlorophyll content, and a concomitant decrease in phenolic acid/chlorophyll ratios; (b) a significant drop in the activity of enzymes of phenylpropanoid metabolism (phenylalanine ammonia-lyase, cinnamate-4-hydroxylase and caffeate-O-methyltransferase); (c) the absence of chalcone-flavanone isomerase activity and a resulting loss of potential for the synthesis of C-glycoflavones; (d) the disappearance of sinapic acid and the formation of a number of unidentified phenolic compounds. While the chloroplast ultrastructure of intact cotyledons exhibited the normal features of light-grown tissues those of the cultured tissues appeared to be partially differentiated and exhibited marked ultrastructural changes which involved: (a) the absence of starch grains and an increase in the number and size of plastoglobuli; (b) a loosely packed thylakoidal system with few lamellae and occassional granal stackings in callus-tissue chloroplasts; (c) a rather “primitive” type of chloroplast with vesiculated lamellar structure and containing phytoferritin bodies in the cultured cells. The parallelism between the biochemical modifications and the changes in chloroplast ultrastructure of callus tissues and cultured cells is discussed in relation to the possible involvement of chloroplasts in penylpropanoid and flavonoid biosynthesis in cultured flax tissues.