Pollen tube distribution in the kiwifruit (Actinidia deliciosa A. Chev. C. F. Liang) pistil in relation to its reproductive process

Abstract

High resolution light and fluorescence microscopy were used to investigate the structural and cytochemical features of the kiwifruit (Actinidia deliciosa) pistil and to follow the pollen tube pathway after pollination. The multicarpellary ovary is syncarpous only at the ovary level thus leaving 30-40 free styles on top. The fusion of the longitudinally-folded carpels to form the syncarpous ovary forms a central parenchymatous axis, the columella, from which the ovules radiate outwards into the ovary cavity. A prominent cup shaped depression on the columella at the top end of the ovary, termed the pollen tube distributor cup (PTDC) was detected. Pollen tubes from the stigma travel through the transmitting tract and enter the PTDC from where they are distributed towards the ovary. Even when pollination is restricted to two stigmas, the PTDC seems to ensure that the pollen tubes are evenly distributed around the ovary resulting in an even distribution of seeds. This suggested role of the PTDC which could compensate for over and under pollination of individual stigmatic arms is another adaptive feature which plays a crucial role in the reproductive process of kiwifruit. The significance of this structure for pollination by insects is discussed.