Effect of Zn deficiency on net photosynthetic rate, 14C partitioning, and oil accumulation in leaves of peppermint

Changes in growth, CO2 exchange rate, and distribution of photosynthetically fixed 14CO2 into the primary photosynthetic metabolic pool (sugars, amino acids and organic acids) and essential oil accumulation were determined in leaves (leaf positions 1-6 from apex) of developing peppermint grown in a solution culture at Zn concentrations of 0 and 0.05 g m-3. There was a significant decrease in 14C incorporation in total, ethanol-soluble and ethanol-insoluble fractions in Zn deficient plants at all leaf positions. 14C incorporated in essential oil and in sugars were significantly higher in leaf pairs 1 to 3 than in leaf pairs 4 to 6. 14C incorporation into amino acids and organic acids was higher in all leaf pairs in Zn deficient plants. Statistical analysis showed a positive significant association between Zn content of leaf and 14C incorporation into ethanol-soluble fraction and sugars and a negative correlation with 14C incorporation into amino acids and organic acids. Hence the content of sugars in leaves significantly influences essential oil accumulation under Zn stress.