Sprout formation in epiphyllous plantlets from detached Bryophyllum calycinum leaves: Relevance for the senescence of mother leaves under drought stress

Abstract

Epiphyllous plantlets / vegetative propagules of Bryophyllum calycinum have been well known to develop only on detached leaves but not in leaves of intact plants. In the present study we have found a morphogenesis that the intact epiphyllous plantlets induce sprouts, but not epiphyllous buds, in plantlet leaves when the mother leaves almost completely senesced under drought stress. Anatomical studies of sprouts showed the presence of vascular connection between sprouts and plantlet leaves. After re-watering isolated plantlets, the growth of existing sprouts was inhibited and most of the primordia of buds in plantlet leaves were little differentiated, they appeared to be dormant and further formation of plantlets was suppressed. The sprouts were not formed when plantlets were connected with green parts of mother leaves. Removal of primordia on the one side of detached mother leaves caused loss of chlorophyll in leaves, and the appearance of plantlets on the other side delayed chlorophyll degradation. These results suggest that development of sprouts from epiphyllous plantlets on detached mother leaves is closely related to leaf senescence induced by severe drought stress. The role of the total senescence of the mother leaves under drought conditions in the induction of sprouts is discussed with respect to hormonal balance and signaling networks.