Spontaneous and induced apoptosis in embryogenic cell cultures of carrot (Daucus carota L.) in different physiological states

Programmed cell death (apoptosis) in plants - and plant cells in culture - has received much less attention than its animal counterpart. In the presen t work, using agents producing biotic or abiotic stress on cultivated cells from carrot - and, in a few experiments, Arabidopsis -, we show that DNA f ragmentation, random or oliogonucleosomal, can be induced by different trea tments. Moreover, we demonstrate that the same cultures may or may not resp ond to the inducing signal according to their physiological state. In parti cular, stationary cells are more responsive to the inducing signal than act ively proliferating ones, and cells growing in an unorganized way are more responsive than cells carrying out the embryogenic programme. Senescent cel ls in culture also appear to die by apoptosis, but healthy cells can also b e induced to die apoptotically if exposed to the medium conditioned by sene scent cells of the same or different species.