Lodicule function and filament extension in the grasses: Potassium ion movement and tissue specialization

Flowering in the grasses has been the subject of a great deal of previous research, yet much remains to be learned concerning the role of environmental and endogenous factors in controlling the actual events of anthesis. The objective of this study has been to investigate further two key processes, namely lodicule function and stamen extension. The lodicules are the two diminutive bodies lying between the lemma and the ovary base in the grass floret which, by expanding rapidly at the time of anthesis, lever away the rigid lemma allowing anthers and stigmas to emerge. Expansion results From the swelling of a cushion of tissue at the base of each lodicule. We show thai this is driven by the influx of water associated with the accumulation of K+ in specialized distensible cells of the basal cushion. The stamen filaments normally elongate synchronously with the enlarging lodicules, again with the passage of K+ into the extending cells. The walls of distensible cells of the lodicule bear lattice-like cellulosic thickenings with transverse bars in an outer layer and longitudinal bars in an inner, a basket-like disposition allowing rapid expansion while preserving the integrity of the protoplast. The microfibrils in the walls of the cylindrical filament cells are disposed helically. constraining expansion to the longitudinal axis. The principal extraneous factors initiating lodicule function in mature florets of rye are mechanical disturbance and light. In the field radiant heat is unlikely to be a dominant factor. In a customarily cleistogamous cultivar of wheat, sporadic florets open chasmogamously in intense light, both lodicules and stamen filaments enlarging. In cleistogamous flowers in the same inflorescence the lodicules fail to enlarge while the filaments extend, suggesting that the influx of osmoticum into the two sets of organs is independently controlled. (C) 1996 Annals of Botany Company.