Light-induced production of antidepressant compounds in etiolated shoot cultures of Hypericum hookerianum Wight & Arn. (Hypericaceae)

Hypericum hookerianum is a lesser known ethnomedicinal plant having wound healing, antitumor and anti-HSV-1 properties. Isolated nodes of in vitro shoots sub-cultured in the dark for 4 weeks on half strength Murashige and Skoog medium solidified with Gelzan (1.5 g l(-1)), and supplemented with 2.325 mu M kinetin produced 8.0 +/- A 0.40 etiolated shoots of 5.0 +/- A 0.62 cm length at 74 % efficiency versus 9.2 +/- A 0.6 healthy shoots of 4.4 +/- A 0.5 cm obtained from nodes in light at 96 % efficiency. Low concentrations of hypericin were found in wild plant [0.35 +/- A 0.09 mg g(-1) dry weight (DW)] and control green shoot cultures (0.91 +/- A 0.03 mg g(-1) DW). Etiolated shoots exposed to a 12 h photoperiod (50 mu mol m(-2) s(-1)) through 1-25 days turned red incrementally due to synthesis and accumulation of 0.1-3.83 mg g(-1) DW hypericin in sub-epidermal cortical cells of the stem and varied shaped cells of the distorted mesophyll. Flavonoid and anthocyanin concentrations of the etiolated shoots subjected to the 12 h photoperiod were 3-5 fold higher than the control shoot cultures while total chlorophylls [1.97 +/- A 0.05 mg g(-1) fresh weight (FW)] of the light exposed shoots were significantly less compared to the control (2.86 +/- A 0.18 mg g(-1) FW) and natural plant (6.82 +/- A 0.29 mg g(-1) FW). HPLC analysis of shoot extracts revealed the presence of 0.14 +/- A 0.03, 0.16 +/- A 0.02 and 1.45 +/- A 0.16 mg g(-1) DW hyperforin in wild plant, control shoot cultures and etiolated shoot cultures illuminated for 25 days, respectively. Despite a reasonable presence in etiolated shoots (0.61 +/- A 0.15 g(-1) FW), total phenols did not increase significantly during illumination. The results indicate light induced synthesis of anti-depressant phenolic derivatives (hypericin, hyperforin and flavonoids) in etiolated shoot cultures of H. hookerianum.