Structural aspects of ovule and seed development and nonrandom abortion inMelilotus officinalis (Fabaceae)

Abstract

Summary.Only one ovule matures into a seed in Melilotus officinalis. Although eight ovules form within an ovary, only the basal ovule develops into a mature seed, whereas the other ovules degenerate. The investigation of ovule and seed structure at different developmental stages and a comparison of quantitative characters of differently fated ovules within an ovary were undertaken by light, phase contrast, and fluorescence microscopy. In this species, campylotropous ovules develop simultaneously on marginal placentae in an apocarpous unilocular gynoecium. Megasporo-and megagametogenesis proceed normally and are completed in bud. The maturation of the Polygonum type embryo sac takes place after the flower opens. Shortly before fertilization, synergids show signs of degeneration in all ovules. At this stage, neither the structure nor the sizes of ovules within one ovary differ significantly. In spite of this, only the basal ovule develops into a seed. Rarely, one of the upper-situated ovules or the basal and another ovule mature into seeds. Seed enlargement is insignificant until the stage when globular embryo and nuclear endosperm are formed. At the seed-filling stage, other ovules have collapsed and the seed gradually comes to occupy the total volume of the pod. The fruit-to-seed length ratio decreases considerably during seed ripening. At fertilization, ovary length is four times greater than ovule length. In the mature state, the fruit and seed lengths are approximately equal. Seed size and weight diminish with an increase in seed number within a pod, although pod size remains constant. It is assumed that nonrandom abortion of young seeds in M. officinalis is under maternal control and is not related to structural abnormalities in ovule development or with limitation in pollen. We suppose that evolution of this species may have proceeded in the direction of a decrease in seed number and an increase in its sizes, which may play an important role in seed dispersal and seedling establishment.

Factors Underlying Seed Yield in Red Clover: Review of Current Knowledge and Perspectives

“…Embryo abortion is a commonly observed phenomenon in legumes, and has been the focus of various studies in forage legumes [80,82,83]. In diploid red clover, Povilaitis [84] found that 70% of ovules developed into mature embryos in high seed-yielding genotypes vs. 40% in low seed-yielding genotypes.…”

Effect of invader removal: pollinators stay but some native plants miss their new friend

“…Using the data gathered, a plant-pollinator interaction network was constructed for the studied community in the presence and after removal of O. pes-caprae. Networks were represented as two-dimensional matrices, with rows representing the plants and columns Galloni et al (2007) * Considering M. officinalis is self-pollinated (Akhalkatsi et al 1999) representing the pollinator species. The cell values expressed the frequency of visits observed for each plant-pollinator interaction.…”

Water limitation effect on seed development and germination in Trigonella coerulea (Fabaceae)

“…It was shown (Rocha and Stephenson, 1991) that Phaseolus coccineus may abort potentially viable seeds. Non-random abortion of young seeds in Melilotus officinalis is under maternal control and is not related to structural abnormalities in ovule development or with limitation in pollen (Akhalkatsi et al, 1999). In apricot, degeneration of the secondary ovule takes place before fertilisation of the primary ovule, independent of pollination, and is a part of a programmed, developmentally regulated process of ovule selection (Rodrigo and Herrero, 1998).…”