Development of Inflorescences in Cymbidium ( Orchidaceae)

Abstract

Microsporogenesis in Cymbidium Sazanami‘Harunoumi’ was investigated cytologically and histochemically in relation to the abortion of inflorescences. The stage of microsporogenesis in basal flower buds was approximately correlated with flower stalk length. Sporogenous cell stage ended with the disappearance of mitotic figures at 4 cm stalk length. Premeiotic G1, S-G2 and meiotic prophase corresponded to 4-5 cm, 4-6 cm and 6-15 cm stalk length, respectively. Then meiotic figures of metaphase I to telophase II were observed in the flower bud on the flower stalk of 15.5 cm in length, but meiosis had not completed. Based on this result the duration of meiosis is also discussed.Effects of high temperature (30°C day/25°C night) on the growth and flowering of inflorescences varied with the developmental stage of flower buds at the treatment. Flower buds at sporogenous cell stage aborted without stalk elongation. Those at meiotic prophase or later stage normally developed to anthesis. In inflorescences at the premeiotic stage flower stalk elongation was induced, though their flower buds dropped without flowering. Therefore the premeiotic stage seemed to be critical for the effect of high temperature. However the critical phase of it could not be determined strictly.The stage at which abortion occurred was also examined by using the inflorescences kept at the high temperature throughout the experiment. Abortive stage of basal flower buds was tentatively estimated to be premeiotic G1 phase based on mitotic activity, nuclear DNA analysis and other floral features. This result showed that microsporogenesis did not proceed into the premeiotic DNA synthetic phase under con-tinuous high temperature condition and resulted in the abortion of the inflorescence.