Seasonal variation in antioxidant enzymes and the sprouting response of Gmelina arborea Roxb. nodal sectors cultured in vitro

Nodal sector explants of Gmelina arborea Roxb. showed seasonal variation in the sprouting of axillary buds in vitro. Explants from mature trees showed only 20% sprouting in summer, while those from seedlings and young trees s howed over 85% sprouting in this season. In winter, there was a significant decrease in the sprouting response of explants from young and mature trees but not in that of seedling explants. We have attempted to correlate the s prouting response of the explants with their antioxidant status. Activities of three enzymes, namely ascorbate peroxidase, superoxide dismutase and gu aiacol-dependent peroxidase which form a part of the antioxidant defense sy stem of plants, were studied in the excised nodal sectors before and after placing them on culture medium. Prior to culture, higher activities of asco rbate peroxidase, superoxide dismutase and guaiacol-dependent peroxidase we re observed during winter than during summer. During the culture period, as corbate peroxidase, superoxide dismutase and guaiacol-dependent peroxidase showed variation depending on the season in which the explants were isolate d, and the age of the donor. Axillary bud sprouting in vitro appeared to de pend more on the physiological state of the donor, than on the oxidative st ress generated during culture.