A comparative study of the effects of gamma radiation on organized and disorganized growth of tobacco

Abstract

A comparative study of the effects of gamma radiation was carried out on young seedlings of tobacco in culture and callus tissue of tobacco grown in suspension culture. A striking difference in radiosensitivity was observed between the two types of growth, viz. organized vs. disorganized growth. Low doses of 650 and 1300 R produced certain initial morphological effects on seedlings like stunting leaf growth and injuring certain cells of the apical meristem; but as the seedlings were allowed to grow for 80 days in culture, these early morphological effects disappeared and a stimulation in growth of seedlings was evident at these low doses. A dose of 5200 R stopped completely the growth of the apical meristem. In comparison, at low doses up to 1300 R, callus growth was slightly reduced and only doses around 10,400 R produced any adverse decrease in growth of callus tissue, with some callus tissues surviving even after a dose of 20,800 R. This difference in radiosensitivity between the meristem of normal seedlings and the callus tissue can be interpreted to be analogous to a “closed system” vs. an “open system”; i.e. the apical meristem representing a “closed system” where the small number of meristematic cells present at the apex are all diploid (with no endopolyploidy occurring) and under the influence of the organizational environment of the intact plant. On the other hand, callus tissue will represent an “open system” where the disorganized proliferating cells are friable, noncoherent and free from each other with a large number of cells in various levels of ploidy. The results are discussed in the light of these observations.