CHANGES IN PROTEIN AND AMINO-ACID LEVELS DURING GROWTH AND SENESCENCEOF NICOTIANA-RUSTICA CALLUS

The degradation of protein, changes in the polysome population and ami no acid levels were investigated during the growth and senescence of t obacco (Nicotiana rustica L. cv. Gansu Yellow Flower) callus. During t he growth period, the synthetic rate of protein increased concommitant ly with the elevation of proteinase activity. After the onset of callu s senescence, a dramatic decline in the polysome population was observ ed after day 25. The activity of proteinase was markedly enhanced betw een day 20 and day 25, and then decreased. The activity of aminopeptid ase was low throughout the growth period and the early stage of senesc ence, and eventually decreased during the late stage of senescence. Th erefore, it is suggested that the loss of proteins is not mainly due t o the role of aminopeptidase but that of proteinase. Free amino acids accumulated rapidly during senescence. The levels of 14 free amino aci ds, except for alanine and cysteine, increased significantly after the onset of senescence.