Developmental Fates of Axillary Buds as a Major Determinant for the Pattern of Life History in Lolium

Abstract

The architecture of a grass population is determined by the spatial distribution and morphology of tillers. The demographic and phase changes of tillers were compared between an annual-like (Progrow) and perennial (Ruanui) lines of Lolium species. We investigated the developmental fate of axillary buds for 57 weeks after germination (WAG) under a constant condition. In general, a high production of seeds is positively correlated with the annual habit in plants. A high production of seeds was highly associated with % reproductive tillers in annual-like Progrow, which resulted from the death of non-reproductive or vegetative tillers before heading. However, no such tendency was observed in perennial Ruanui. This showed that the death of tillers is genetically regulated to contribute to the maximum success in fitness depending on the longevity. In addition, % reproductive tillers was distinctly reduced during the following regrowth in Ruanui, suggesting that a phase change in the tiller system took places during the growth. Microscopic observations of quiescent axillary buds showed that a phase change from reproductive to vegetative occurred at maturity in Ruanui but not in Progrow. As a result, numerous ears developed in Ruanui plants only when they were vernalized after first maturation (30 WAG), showing that the vernalized state gradually diminishes with time in Ruanui. Thus, the present results confirmed that the differential regulation in the developmental fate of axillary buds actually plays a role for determining the pattern of life history in Lolium.