First evidence of a calcium transient in flowering plants at fertilization.

We report here the first evidence of a transient elevation of free cytosolic Ca2+ following fusion of sperm and egg cell in a flowering plant by the use of an in vitro fertilization system recently developed in maize. Imaging changes in cytosolic Ca2+ at fertilization was undertaken by egg cell loading with the fluorescent Ca2+ indicator dye fluo-3 under controlled physiological conditions. The gamete adhesion step did not induce any cytosolic Ca2+ variation in the egg cell, whereas the fusion step triggered a transient cytosolic Ca2+ rise in the fertilized egg cell, lasting several minutes. This rise occurred after the establishment of gamete cytoplasm continuity. Through these observations, we open the way to the identification of the early signals induced by fertilization in flowering plants that give rise to the calcium transient and to investigations of the role of Ca2+ during egg activation and early zygote development in plants, as has been reported for other better characterized animal and algae systems.