Micropropagation of Cassia occidentalis L. and the effect of irradiance on photosynthetic pigments and antioxidative enzymes

The objective of the current study was to develop an efficient and reproducible protocol for plant regeneration using nodal (1.0-1.5 cm) explants excised from a field grown mature plant of Cassia occidentalis L. The highest shoot regeneration frequency (80 %) with a maximum number of shoots (11.66) and shoot length (3.83 cm) after eight weeks of culture were observed on a Murashige and Skoog (MS) medium amended with 5.0 mu M 6-benzyladenine, 100 mu M citric acid, and 1.0 mu M alpha-naphthalene acetic acid. A half-strength MS medium supplemented with 1.5 mu M indole-3-butyric acid proved best for the induction of maximum roots (8.33) per shoot. Plantlets with well-developed shoots and roots were successfully acclimatized in plastic pots containing sterile Soilrite under two irradiances of 50 and 300 mu mol m(-2) s(-1) (LI and HI, respectively) in a culture room, and after transfer to the field, the survival rate was 70 %. A significant increase in chlorophyll, carotenoid, and malondialdehyde content was found during acclimatization under both the irradiances but higher under HI. Similarly, the activities of superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase increased more under HI. Plantlets acclimatized under HI exhibited a better growth than those under LI.