Pollen movement in the micropylar canal ofLarix and its simulation

Abstract

InLarix pollen captured by the ovule and rested at the distal end of the micropylar canal is transferred upward to the nucellus before it develops a pollen tube. This upward movement occurs after the canal is filled with secreted fluid, despite the fact that the pollen sinks in the fluid. We examined the mechanism of the movement based on the morphology of the canal and its simulation using pipettes. When a water column moves upward in a waxed pipette, suspended particles also move upward carried by the meniscus. InL. x eurolepis the inner surface of the integument lining the micropylar canal is coated by a cuticle layer. This layer is further coated by an integumentary membrane before the fluid is secreted. This membrane, however, becomes distorted or disappears during fluid secretion. The exposed cuticle and the degenerated hydrophilic nucellar apex may facilitate the movement of the meniscus toward the nucellus as in the simulated pipette. Pollen is interpreted to move by being carried by the meniscus when the fluid recedes.