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 previ ous research, yet much remains to be learned concerning the role of en vironmental 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 t he ovary base in the grass floret which, by expanding rapidly at the t ime of anthesis, lever away the rigid lemma allowing anthers and stigm as to emerge. Expansion results From the swelling of a cushion of tiss ue at the base of each lodicule. We show thai this is driven by the in flux of water associated with the accumulation of K+ in specialized di stensible cells of the basal cushion. The stamen filaments normally el ongate synchronously with the enlarging lodicules, again with the pass age 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-lik e disposition allowing rapid expansion while preserving the integrity of the protoplast. The microfibrils in the walls of the cylindrical fi lament cells are disposed helically. constraining expansion to the lon gitudinal axis. The principal extraneous factors initiating lodicule f unction in mature florets of rye are mechanical disturbance and light. In the field radiant heat is unlikely to be a dominant factor. In a c ustomarily cleistogamous cultivar of wheat, sporadic florets open chas mogamously in intense light, both lodicules and stamen filaments enlar ging. In cleistogamous flowers in the same inflorescence the lodicules fail to enlarge while the filaments extend, suggesting that the influ x of osmoticum into the two sets of organs is independently controlled . (C) 1996 Annals of Botany Company.