Seed abortion in an animal dispersed species, Syzgium cuminii (L.) Skeels (Myrtaceae): the chemical basis

Abstract

In Syzygium cuminii, an animal dispersed species, invariably only one of the 30 ovules develops to maturity. Arathi and Arathi et ah² hypothesized that the abortion could be mediated by an intense intra-fruit sibling rivalry to gain dispersal advantage. They showed that aqueous extract of dominant seeds causes the abortion of healthy subordinate seeds while extracts of maternal tissue such as fruit coat tissue do not. In this paper, we show that the abortion is caused by the inhibition of resource uptake by the subordinate seeds. Extracts of the dominant seeds significantly inhibited the uptake of radioisotope labelled sucrose by healthy subject seeds, when compared to extracts from maternal tissue (fruit coat tissue) and unfertilized ovules. Inhibition was also caused by the diffusates from the dominant seeds. Thin layer chromatography and indirect ELISA indicated the presence of indole compounds in the diffusate. HPLC analysis indicated the presence of a single retention peak in the diffusate with a substantial overlap with that of indoleacetic acid and contained most of the functional chemical causing the abortion. We propose that the chemical involved in the abortion of seeds might be a small molecular weight, highly diffusible indole compound.