N.K. Srivastava

Influence of gibberellic acid on 14CO2 metabolism, growth, and production of alkaloids in Catharanthus roseus

Changes in growth parameters, carbon assimilation efficiency, and utilization of 14CO2 assimilate into alkaloids in plant parts were investigated at whole plant level by treatment of Catharanthus roseus with gibberellic acid (GA). Application of GA (1 000 g m−3) resulted in changes in leaf morphology, increase in stem elongation, leaf and internode length, plant height, and decrease in biomass content. Phenotypic changes were accompanied by decrease in contents of chlorophylls and in photosynthetic capacity. GA application resulted in higher % of total alkaloids accumulated in leaf, stem, and root. GA treatment produced negative phenotypic response in total biomass production but positive response in content of total alkaloids in leaf, stem, and roots. 14C assimilate partitioning revealed that 14C distribution in leaf, stem, and root of treated plants was higher than in untreated and variations were observed in contents of metabolites as sugars, amino acids, and organic acids. Capacity to utilize current fixed 14C derived assimilates for alkaloid production was high in leaves but low in roots of treated plants despite higher content of 14C metabolites such as sugars, amino acids, and organic acids. In spite of higher availability of metabolites, their utilization into alkaloid production is low in GA-treated roots.

Influence of Etherel and Gibberellic Acid on Carbon Metabolism, Growth, and Essential Oil Accumulation in Spearmint (Mentha Spicata)

Changes in growth parameters and 14CO2 and [U-14C]-sucrose incorporation into the primary metabolic pools and essential oil were investigated in leaves and stems of M. spicata treated with etherel and gibberellic acid (GA). Compared to the control, GA and etherel treatments induced significant phenotypic changes and a decrease in chlorophyll content, CO2 exchange rate, and stomatal conductance. Treatment with etherel led to increased total incorporation of 14CO2 into the leaves wheras 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 etherel 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 essential oils compared to the control. When 14CO2 was fed to 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. Etherel and GA influence the partitioning of primary photosynthetic metabolites and thus modify plant growth and essential oil accumulation.

Zn-acquisition and its role in growth, photosynthesis, photosynthetic pigments, and biochemical changes in essential monoterpene oil(s) of Pelargonium graveolens

Culturing geranium at different doses of Zn from 0–1.0 g m−3 (Zn0 to Zn1.000) revealed that Zn is an antioxidant promoter, apart from its micronutrient essentiality. Zn0.250 was the critical concentration for maximum content (0.21 %) of total essential monoterpene oil(s). At Zn0.005-Zn0.250, net photosynthetic rate, and contents of chlorophyll and essential monoterpene oil(s) were affected. The maximum peroxidase activity was obtained at Zn0.250, with the production of biomolecule geraniol. We found an oxido-reducible reaction of Zn in the formation of monoterpene essential oil(s) and possibly major constituents of geraniol.

Distribution of photosynthetically fixed 14CO2 into essential oil in relation to primary metabolites in developing peppermint (Mentha piperita) leaves

Abstract Changes in essential oil content, CO 2 exchange rate and distribution of photosynthetically fixed 14 CO 2 into essential oil, amino acids, organic acids and sugars were determined in developing peppermint leaves. The incorporation of 14 CO 2 into sugars was maximal followed by organic acids, amino acids and essential oil at all stages of leaf development. The incorporation into sugars and amino acids declined as the leaf matured whereas that in essential oil and organic acids increased with leaf expansion and then decreased.

Boron Deficiency Induced Changes in Translocation of 14CO2-Photosynthate Into Primary Metabolites in Relation to Essential Oil and Curcumin Accumulation in Turmeric (Curcuma longa L.)

Changes in leaf growth, net photosynthetic rate (PN), incorporation pattern of photosynthetically fixed 14CO2 in leaves 1–4 from top, roots, and rhizome, and in essential oil and curcumin contents were studied in turmeric plants grown in nutrient solution at boron (B) concentrations of 0 and 0.5 g m-3. B deficiency resulted in decrease in leaf area, fresh and dry mass, chlorophyll (Chl) content, and PN and total 14CO2 incorporated at all leaf positions, the maximum effect being in young growing leaves. The incorporation of 14CO2 declined with leaf position being maximal in the youngest leaf. B deficiency resulted in reduced accumulation of sugars, amino acids, and organic acids at all leaf positions. Translocation of the metabolites towards rhizome and roots decreased. In rhizome, the amount of amino acids increased but content of organic acids did not show any change, whereas in roots there was decrease in contents of these metabolites as a result of B deficiency. Photoassimilate partitioning to essential oil in leaf and to curcumin in rhizome decreased. Although the curcumin content of rhizome increased due to B deficiency, the overall rhizome yield and curcumin yield decreased. The influence of B deficiency on leaf area, fresh and dry masses, CO2 exchange rate, oil content, and rhizome and curcumin yields can be ascribed to reduced photosynthate formation and translocation.

Influence of Mn Deficiency on Growth, Chlorophyll Content, Physiology, and Essential Monoterpene Oil(s) in Genotypes of Spearmint (Mentha Spicata L.)

Spearmint cultivars MSS-5, Arka, and Neera grown in nutrient culture in controlled conditions differed in plant height, number of tillers, internodal position, fresh mass, dry mass, leaf stem ratio, and chlorophyll contents. Initial transpiration rate, stomatal conductivity, and CO2 exchange rate showed better increase in MSS-5 genotype. Mn stress decreased oil content whereas the content of oil constituent carvone increased in MSS-5 and Arka.

Distribution of photosynthetically fixed 14CO2 into curcumin and essential oil in relation to primary metabolites in developing turmeric (Curcuma longa) leaves

Abstract Changes in essential oil, CO 2 exchange rate and distribution of photosynthetically fixed 14 CO 2 into curcumin, essential oil, amino acids, organic acid and sugars were determined in developing leaves, rhizome and roots of turmeric. Of the total 14 CO 2 assimilated by plants, first, second, third and fourth leaves fix 31, 23, 21 and 9%, roots 4%, rhizome 6%, oil 0.01% and curcumin 4.6% of gm. fresh weight rhizome. Leaf area, its fresh and dry weight and CO 2 exchange rate increase up to third leaf. The incorporation of 14 CO 2 into sugars was maximal followed by organic acid, amino acid and essential oil at all stages of leaf development. Assimilates translocated to roots and rhizome showed similar trend of incorporation in fractions as in leaves. Youngest developing leaves assimilated maximum 14 CO 2 into metabolites and essential oil. In rhizome curcumin constitutes a major metabolite. The incorporation of 14 CO 2 into metabolites and oil declined as the leaves matured with youngest leaf being physiologically most active. A major portion of 14 CO 2 assimilated is translocated to roots, and curcumin formation in rhizome. The study highlights that metabolites from the photosynthetic pathway are incorporated in curcumin.

Partitioning of 14C-Photosynthate of Leaves in Roots, Rhizome, and in Essential Oil and Curcumin in Turmeric (Curcuma longa L.)

Incorporation of photosynthetically fixed 14C was studied at different time intervals of 12, 24, and 36 h in various plant parts—leaf 1 to 4 from apex, roots, and rhizome—into primary metabolites—sugars, amino acids, and organic acids, and secondary metabolites—essential oil and curcumin—in turmeric. The youngest leaves were most active in fixing 14C at 24 h. Fixation capacity into primary metabolites decreased with leaf position and time. The primary metabolite levels in leaves were maximal in sugars and organic acids and lowest in amino acids. Roots as well as rhizome received maximum photoassimilate from leaves at 24 h; this declined with time. The maximum metabolite concentrations in the roots and rhizome were high in sugars and organic acids and least in amino acids. 14C incorporation into oil in leaf and into curcumin in rhizome was maximal at 24 h and declined with time. These studies highlight importance of time-dependent translocation of 14C-primary metabolites from leaves to roots and rhizome and their subsequent biosynthesis into secondary metabolite, curcumin, in rhizome. This might be one of factors regulating the secondary metabolite accumulation and rhizome development.

Utilization of Photosynthetically Fixed 14CO2 into Alkaloids in Relation to Primary Metabolites in Developing Leaves of Catharanthus roseus

Partitioning of current photosynthates towards primary metabolites and its simultaneous incorporation in leaf alkaloids was investigated in developing leaves of medicinally important Catharanthus roseus. Of the total 14CO2 assimilated, the leaves at positions 1–6 fixed 8, 22, 25, 19, 13, and 8 %, respectively, and stem 3 %. Leaf fresh mass, chlorophyll content, and CO2 exchange rate increased up to the third leaf. The total alkaloid content was highest in young actively growing leaves, which declined with age. Total 14C fixed and its content in ethanol soluble fraction increased up to the third leaf and then declined. The 14C content in primary metabolites such as sugars and organic acids was also highest in the 3rd leaf. The utilization of 14C assimilates into alkaloids was maximum in youngest leaf which declined with leaf age. Hence the capacity to synthesize alkaloids was highest in young growing leaves and metabolites from photosynthetic pathway were most efficiently utilized and incorporated into alkaloid biosynthetic pathway by young growing leaves.

Variation among commercial cultivars of Japanese mint ( Mentha arvensis L.) in the morphological and metabolite characters associated with essential oil yield

Summary Intraspecific variation in four widely cultivated cultivars of Japanese mint ( Mentha arvensis L.) was studied to understand the physiological basis of regulation of essential oil accumulation. The cultivars had the same oil biosynthetic route but differed in morphological/physiological characters. Oil content showed significantly positive correlations with yield traits like leaf and stem fresh and dry weights, relative growth rate and CO2 exchange rate. Leaf area per plant was positively associated with herb yield. Observation that leaf fresh and dry weights possessed higher significant genotypic correlation coefficients than phenotypic correlation coefficients indicated that these traits express a strong genetic influence on oil yield, as the latter incorporates the former. Photosynthetic efficiency measured by uptake and fixation of 14CO2 and 14C-sucrose showed differential utilization of these precursors. Sucrose was more efficiently utilized for oil biosynthesis than photoassimilated (14CO2) precursors. The levels of metabolites fixed through 14CO2 remained lower than those fixed via 14C-sucrose. Efficient cultivars translocated a greater portion of metabolite towards essential oil and also accumulated higher concentrations of nutrients. The concentrations of the micronutrients Fe, Mn, Cu, Zn varied significantly among cultivars with leaves showing higher concentrations than stems. It is evident that the physiological capability of mints in terms of leaf growth,nutrient uptake, photosynthetic capacity, partitioning and distribution of assimilated metabolites in leaf and stem, contribute significantly to biosynthesis and accumulation.