D. Howpage et al., POLLEN-TUBE DISTRIBUTION IN THE KIWIFRUIT (ACTINIDIA-DELICIOSA A. CHEV. LIANG,C.F.) PISTIL IN RELATION TO ITS REPRODUCTIVE PROCESS, Annals of botany, 81(6), 1998, pp. 697-703
High resolution light and fluorescence microscopy were used to investi
gate the structural and cytochemical features of the kiwifruit (Actini
dia deliciosa) pistil and to follow the pollen tube pathway after poll
ination. The multicarpellary ovary is syncarpous only at the ovary lev
el thus leaving 30-40 free styles on top. The fusion of the longitudin
ally-folded carpels to form the syncarpous ovary forms a central paren
chymatous axis, the columella, from which the ovules radiate outwards
into the ovary cavity. A prominent cup shaped depression on the colume
lla at the top end of the ovary, termed the pollen tube distributor cu
p (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 distribute
d around the ovary resulting in an even distribution of seeds. This su
ggested role of the PTDC which could compensate for over and under pol
lination of individual stigmatic arms is another adaptive feature whic
h plays a crucial role in the reproductive process of kiwifruit. The s
ignificance of this structure for pollination by insects is discussed.
(C) 1998 Annals of Botany Company.