Temporal patterns of gamete production within individuals of Raphanus sativus (Brassicaceae)

Abstract

Previous studies on the deployment of energy to male and female gametes in plants have concentrated on differences among individuals or among related species. We documented temporal patterns of sex allocation within individual wild radish plants grown under controlled conditions. Lifetime investments in pollen and ovules were determined for four unrelated individuals of Raphanus sativus L. (Brassicaceae). Each individual produced 600–1100 flowers over the approximately 5-week flowering period. Mature floral buds were collected daily and ovule number, pollen grain number, pollen size, and pollen to ovule ratio (P:O) were determined for each. Variation in these traits was partitioned into variation among plants and among dates (representing flowering sequence). There was significant variation among plants for all characters, but because plants responded differently to date for three of the characters, further analyses were performed on a plant-by-plant basis. All plants showed significant reductions in pollen number and P:O through time, three plants showed a significant reduction in pollen size with time, and two plants showed a significant reduction in ovule number with time. The observed variation in phenotypic gender among these plants was not environmentally mediated because all plants were grown together in a controlled environment and therefore the differences in allocation to gametes were due to genetic or developmental differences. A result of intraspecific variation in gamete production is that the success of each individual as a male and female parent is likely to vary both within the population and within the flowering season. Key words: pollen to ovule ratio, Raphanus, pollen number, temporal changes, phenotypic gender, Brassicaceae, radish.