Abstract
Spring ephemerals are a group of herbaceous plants that fulfill their life cycle on the floor of deciduous forests in temperate and boreal regions during a short period of time between snowmelt and closure of canopy of trees. Near the closure, synchronous voluntary senescence of their aboveground parts occurs and underground storage organs lie dormant until the next spring. An endogenous factor must be involved in this rapid synchronous senescence. Strong senescence-promoting activity was detected in extracts of shoots of a spring ephemeral, Gagea lutea, by a bioassay. The active compound was identified as free a-linolenic acid. The level of linolenic acid was very low one week before flowering, increased rapidly with time and reached a maximum one week after flowering. Senescence became prominent thereafter. These results suggest that the senescence is triggered by an accumulation of linolenic acid. Maintenance of shoots on the dim forest floor must cause a deficit of storage compounds. To minimize the cost, spring ephemerals seem to have acquired voluntary active senescence thereby filling a narrow niche on the forest floor.
