COLD-SENSITIVE EXPRESSION OF CYTOKININ HABITUATION BY TOBACCO PITH CELLS IN CULTURE

Cloned, cytokinin-habituated tissues of Nicotiana tabacum L. cv. Havana 425 grow in culture at 25.degree. C without added cytokinin. These tissues vary in their expression of the habituated phenotype at 16.degree. C. When cytokinin-requiring pith tissues are converted to the habituated state by 35.degree. C treatment, all habituated cells are cold sensitive. After several transfers in culture, some give rise to stable, cold resistant variants. Both phenotypes are inherited by individual cells. Cold sensitive clones at 16.degree. C and non-habituated clones at 16.degree. C and 25.degree. C show the same dose response to kinetin. At the physiological level, cold sensitivity apparently results from a decreased production of cell division factors rather than from a decreased affinity of cellular receptors for these factors.