Abstract

Changes in growth parameters and ¹⁴C0₂ and [U-¹⁴C]-sucrose incorporation into the primary metabolic pools and diterpene 10 DAB compound were investigated in leaves and stems of Taxus wallichiana Zucarnii treated with gibberellic acid (GA) and inoculated with arbuscular mycorrhizae (AM). Compared to the control, GA(1000 ppm) and AM (1 kg/ha each) with AM-GA combined treatments,  induced significant phenotypic changes and a decrease in chlorophyll content, CO₂exchange rate and stomatal conductance. Treatment with AM-GA led to increased total incorporation of CO₂ into the leaves whereas total incorporation from ¹⁴C sucrose was decreased. When ¹⁴CO₂ was fed, the incorporation into the ethanol soluble fraction, sugars, organic acids, and essential oil was significantly higher in AM-GA treated leaves than in the control. However, [U-¹⁴C] -sucrose feeding led to decreased label incorporation in the ethanol-soluble fraction, sugars, organic acids, and diterpenes compared to the control. When ¹⁴C0₂ was fed to AM-GA treated leaves, label incorporation in ethanol-insoluble fraction, sugars, and oils was significantly higher than in the control. In contrast, when [U-¹⁴C]-sucrose was fed the incorporation in the ethanol soluble fraction, sugars, organic acids, and oil was significantly lower than in the control. Hence the hormone treatment induces a differential utilization of precursors for oil biosynthesis and accumulation and differences in partitioning of label between leaf and stem. GA and GA-VAM influence the partitioning of primary photosynthetic metabolites and thus modify plant growth and 10-DAB compound accumulation.

Key words: Amino acids, chlorophyll, CO₂- and C-sucrose incorporation, organicacids, primary photosynthetic metabolites, stem, stomatal conductance, sugars, transpiration rate.