Direct shoot organogenesis from leaf explants of Populus deltoides and changes in selected enzymatic activities

The direct shoot organogenesis was achieved from leaf explant of two commercially important clones of Populus deltoides on MS medium enriched with 15 mg/l adenine sulphate, 5 mg/l Ascorbic acid, 250 mg/l (NH4)(2)SO4 (referred to as PD1 medium) supplemented with 2.5 mu M each of 6-benzylaminopurine and indole-3-acetic acid. Higher shoot organogenic potential was recorded from the explants of clone 'G48' as compared to clone 'L34'. The age of leaf explant also affected the shoot organogenic potential, and maximum shoot organogenesis was recorded in case of 5th leaf from the top of microshoot. Histological studies revealed altered cell division resulting in the formation of meristematic pockets after 5 days of culture, these meristematic pockets grew into dome protuberances by 10th day. Organized shoots were visible after 15 days of culture. A clear three phases of shoot organogenesis viz induction (0-4 days), initiation and organization (4-10 days) and growth (11-16 days onwards) were observed. Marked variation in the activity of enzymes such as catalase, peroxidase, polyphenol oxidase and acid phosphatase was observed during these phases. The activity of these enzymes was found to increase in cultures grown on the medium resulting in shoot organogenesis during shoot development (after 7 days of culture).