Abscisic acid involvement in the induction of summer-dormancy in Poa bulbosa, a grass geophyte

Summer-dormancy occurs in geophytes that inhabit regions with a Mediterranean climate (mild, rainy winters and hot, dry summers). The environmental control of summer-dormancy and the involvement of phytohormones in its induction have been little studied. Poa bulbosa L. is a perennial grass geophyte in which summer-dormancy is induced by long days and by high temperature. Prolonged treatment with ABA (0.1-1.0 mM) under non-inductive 8-h short days (SD) resulted in cessation of leaf and tiller production and in the development of typical features of dormancy: bulbing at the base of the tillers and leaf senescence. Short-term applications of ABA had similar effects but dormancy was transient, i.e. after a short while, leaf growth from the formed bulbs was resumed. ABA treatment of plants growing under an inductive 16-h photoperiod (LD) enhanced the onset of dormancy. Endogenous levels of ABA in leaf blades and at the tiller base (where the bulb develops) increased markedly after the plants were transferred from SD to LD. This increase was greater in the tiller base, and concomitant with bulb maturation. High temperature (27/22 vs 22/17°C) accelerated both bulb development and ABA accumulation in leaf blades. These results suggest that ABA plays a key role in the photoperiodic induction and development of summer-dormancy in P. bulbosa.