Abstract: Temperature-sensitive mutant cell line ts-59 of carrot (Daucus carota L. ) was selected in one of the authors, Dr. Zinmy Renee Sung’s lab from a haploid line HA which was derived from a domesticated carrot variety Juwarot. Callus clumps of cell line ts-59 are composed of embryonic and vacuolated parenchymatous cells. The former shows vigorous cell division activities and appears typical characteristics of meristematic cells；the latter possesses a central vacuole with cytoplasm appressed against the cell wall. The disintegration of the cytoplasm and cell wall of vacuolated cells causes a callus clump fragmenting into several small ones. At normal room temperature (24℃), the calli of ts-59 incubated in liquid Bs medium without 2, 4-D differtentiate into various stages of somatic embryoids. At higher temperature (32℃), the calli can only differentiate into globular stage embryoids. Their component cells appear highly vacuolated. Prolongation of culture period at 32℃ causes disappearance of tonoplast and the limiting membranes of plastids and mitochondria, autolysis of cytoplasm and disintegration of cell wall. Results show that the destruction of membranous systems of cells causes necrosis of the component cells, leading to the abortion of globular embryoids.

Key words: Daucus carota, Temperature-sensitive cell line, Somatic embryogenesis