Effects of ovule and seed abortion on brood size and fruit costs in the leguminous shrub Caesalpinia gilliesii (Wall. ex Hook.) D. Dietr

Ana Calviño

doi:10.1590/s0102-33062014000100006

Abstract

For several plant species, brood size results from the abortion of ovules and seeds. However, these processes have rarely been studied together in wild plants. In some of the leguminous species studied, seed abortion has been found to depend on pollen quality and on the position of the ovule or fruit. The direct consequence for the mother plant is that fruit costs increase as the seed:ovule ratio decreases. However, because ovule abortion occurs earlier than does seed abortion, the former can reduce the biomass invested per seed (i.e., fruit costs) more efficiently than does the latter. Here, the frequencies of aborted ovules and seeds were analyzed in relation to the type of pollination treatment (open pollination vs. hand cross-pollination) and ovule/fruit position within pods of the leguminous shrub Caesalpinia gilliesii. The influence of ovule and seed abortion on fruit costs was analyzed by comparing the pericarp mass per seed between fruits with different frequencies of aborted ovules and seeds. The rate of ovule abortion was similar between hand cross-pollinated and open-pollinated fruits but was higher than that of seed abortion in one- and two-seeded fruits, as well as in those at stylar positions and in distal fruits. Hand cross-pollination reduced seed abortion but did not increase the seed:ovule ratio. In addition, fruits that aborted ovules were found to be less costly than were those that aborted seeds. From the mother plant perspective, these results indicate that ovule abortion is a more efficient mechanism of reducing fruit costs than is seed abortion, because fertilization opportunities decrease with position, and show that brood size is significantly influenced by the fate of the ovule at the pre-zygotic stage.

Highlights

The final number of seeds within a fruit is the result of a sequential process that starts with an initial number of ovules in the ovary and ends with the successful development of fertilized ovules
Seed abortion, which occurs at different developmental stages within the fruit, has been shown to be non-random and based on the genotype of the embryo (Korbecka et al 2002); lower seed:ovule ratios can result from the abortion of unfertilized ovules within the fruit
Both pre-zygotic and post-zygotic ovule abortion contributed to the brood size observed in Caesalpinia gilliesii, with ovule abortion being more important than seed abortion in one- and two-seeded fruits

Summary

Introduction

The final number of seeds within a fruit is the result of a sequential process that starts with an initial number of ovules in the ovary and ends with the successful development of fertilized ovules. In plants in which predation is not a critical factor for seed production, the upper limit for seed number per fruit is set by the number of ovules in the ovary, and the final seed:ovule ratio is mainly determined by fertilization success and seed abortion. Differential ovule receptivity at flower anthesis has been shown to reduce the number of fertile ovules in several leguminous plants (Sengupta & Tandon 2010). Unreceptive ovules have been shown to abort before fertilization in leguminous species, as studied by Sengupta and Tandon (2010)

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