Prefertilization events in ovules of Pseudotsuga: Ovular secretion and its influence on pollen tubes

A natural ovular secretion from the megagametophyte, essential to sexual reproduction, was examined in Pseudotsuga. This secretion began soon after egg formation or about 1 week before fertilization. Secreted fluid filled the micropylar canal. Morphological study showed that the fluid affected (i) dissolution of intine materials; (ii) pollen distortion that may relate to prezygotic selection; and, (iii) induction of pollen tubes. The origin of the secreted fluid is interpreted from an experiment using homogenates. Elongated pollen supplied with a homogenate of the megagametophyte shows immediate movement of starch grains and body cell. Some pollen formed pollen tubes. Homogenates of the nucellus or the integument elicited little or no response. If ovules are dissected before the natural secretion and kept in high relative humidity, the micropylar canal becomes filled with fluid. This fluid is an artifact resulting from dissection, but is also capable of inducing pollen tubes.