The effect of thermal shock on the division cycle of meristematic cells

Abstract

Abstract. The dynamic adaptation of a meristem to a thermal change from 15 to 35°C has been studied. A gradual drop occurs in the mitotic index during the first 6 hr after the change, while the percentage of prophases drops less steeply. At the same time the phenomenon of nucleolar segregation is observed. By making use of a cell population morphologically differentiated as binucleate (by ‘labelling’ with caffeine), it was possible (a) to prove that prophase is specifically prolonged and (b) to locate a highly thermosensitive segment of interphase, situated in the middle of the S period, and apparently coinciding with the sub‐period S, described in the same material as characterized by a decrease in the rate of DNA synthesis. The lengthening of prophase and nucleolar segregation resemble the effects produced by drugs which inhibit RNA synthesis. Intermittent thermal shocks are suggested as a possible means for synchronizing the division cycle of plant cells.