Sucrose mobilization in relation to essential oil biogenesis during palmarosa (Cymbopogon martinii Roxb. Wats. var. motia) inflorescence development.

ABSTRACT

Palmarosa inflorescence with partially opened spikelets is biogenetically active to incorporate [U-14C]sucrose into essential oil. The percent distribution of 14C-radioactivity incorporated into geranyl acetate was relatively higher as compared to that in geraniol, the major essential oil constituent of palmarosa. At the partially opened spikelet stage, more of the geraniol synthesized was acetylated to form geranyl acetate, suggesting that majority of the newly synthesized geraniol undergoes acetylation, thus producing more geranyl acetate. In vitro development of palmarosa inflorescence, fed with [U-14C]sucrose, resulted in a substantial reduction in percent label from geranyl acetate with a corresponding increase in free geraniol, thereby suggesting the role of an esterase in the production of geraniol from geranyl acetate. At time course measurement of 14CO2 incorporation into geraniol and geranyl acetate substantiated this observation. Soluble acid invertase was the major enzyme involved in the sucrose breakdown throughout the inflorescence development. The activities of cell wall bound acid invertase, alkaline invertase and sucrose synthase were relatively lower as compared to the soluble acid invertase. Sucrose to reducing sugars ratio decreased till fully opened spikelets stage, concomitant with increased acid invertase activity and higher metabolic activity. The phenomenon of essential oil biosynthesis has been discussed in relation to changes in these physiological parameters.