Secondary Metabolism-Inducing Treatments During in vitro Development of Turmeric (Curcuma longa L.) Rhizomes

Abstract

Turmeric (Curcuma longa L.) plants that were grown in vitro for 17 or 22 weeks as a fed-batch culture in 2.5 L vessels yielded 39 to 43 g and 62 to 70 g of fresh rhizomes per vessel, respectively (95 % confidence interval). The MS liquid medium was maintained at 6 % sucrose through media addition twice during the experiment. Various methods were employed in attempts to increase secondary metabolism. Antioxidant and total phenolics assays were employed to characterize phytochemical activity. A first experiment exposed four clones to phenylalanine and/or methyl jasmonate (MeJa) from week 12 to 17 in culture. In a second experiment, a clone was given short-term exposure (1.5 weeks) to either proline, a natural proline-rich fish extract, MeJa, or chitosan beginning during the twentieth week of culture. This experiment also included a nitrogen stress treatment (weeks 16–22). The 5-week phenylalanine and MeJa treatments lowered biomass accumulation and antioxidant capacity of the tissue. The magnitude of antioxidant depression was dependent on genotype and, within each genotype, the degree of depression was similar for phenylalanine and MeJa, alone and in combination. In the second experiment, only the low-nitrogen treatment yielded an increase in phenolic content to 4.7 % of dry weight compared to untreated microrhizomes (4.1 % of dry weight). Nitrogen-stressed plants also had less leaf growth, but rhizome mass was unaffected and averaged 63 g FW per vessel. None of the short-term treatments had a significant effect on biomass, antioxidant capacity, or phenolic content. None of the treatments significantly affected radical scavenging, although the low-nitrogen treatment might have improved this activity (p = .1207). Results indicated that plants grown in a high-nitrogen MS media were not responsive to elicitation.

KEYWORDS:

• antioxidant
• phenolics
• chitosan
• curcumin
• DPPH*
• methyl jasmonate
• phenylalanine
• spice