Involvement of nucellar cell death in the pollen tube elongation in gymnosperms -A comparison between Pinus densiflora and Cryptomeria japonica

• Published in: Journal of plant research Vol. 119; p. 173
• Main Authors: Hiratsuka, R, Nakamura, N, Terasaka, O
• Format: Journal Article
• Language: English
• Published: 01.12.2006
• ISSN: 0918-9440

To clarify the relation between pollen tube elongation and nucellar cell death in gymnosperms, we compared P. densiflora with C. japonica, which respectively require 14 and 3 months from pollination to fertilization. The pollen tube branches formed in both species, but the tube protrusion that invades the nucellar cell was observed only in P. densiflora. The release of vesicles from dying nucellar cells and endocytosis of the vesicles by tube were observed in both species. Both tube walls were labeled with the monoclonal antibody JIM13 (against arabinogalactan protein), but not labeled with JIM7 (against pectin). In P. densiflora, nucellar cells in the layer around the tube died and were TUNEL- positive, but in C. japonica only cells in direct contact with the tube died and were TUNEL-negative. During nucellar cell death, chromatin condensation, autophagy and secondary wall formation were observed only in P. densiflora. Starch grains accumulated in the nucellar cells around the tube tip of P. densiflora but not found in C. japonica. These findings suggest that nucellar cell death in P. densiflora involved programmed cell death which was apoptosis-like, and participated in the formation of the aisle and the supply of nutritional materials for tube elongation. In C. japonica, nucellar cell death was not apoptosis-like and the dead cells supplied nutrient materials to pollen tube less actively than those of P. densiflora. It was asummed that the differences between P. densiflora and C. japonica resulted from the differences in the required intervals from pollination to fertilization.