Effects of Exposure to High Temperature at Different Developmental Stages of Shoots on Rosette Formation and Flower Malformation of Gypsophila paniculata L

Abstract

To determine flowering responses with respect to rosette formation and flower malformation, Gypsophila paniculata L, plants at different developmental stages were exposed to high temperatures after exposure to winter chilling.
Initial exposure of vegetative shoots to 30°C from 6:00 to 18:00 and 25°C from 18:00 to 6:00 from 31 Mar. to 10 Apr. resulted in rosette formation in those plants which require long durations of winter chilling such as ‘Perfecta’ and ‘Bristol Fairy’ line 20. Rosette formation occurred even when these plants were grown under optimum conditions. About 50% of the ‘Diamond’ and ‘Bristol Fairy’ line 03 shoots formed rosettes after exposure to 30°/25°C; these cultivars require a relatively lengthy exposure to winter chilling to satisfy their rest requirement. Conversely, ‘Flamingo’, ‘Red Sea’, and ‘Bristol Fairy’ line 08 which require a little chilling did not form rosettes but bloomed.
Exposure to high temperature immediately after the onset of flower bud initiation resulted in shorter flower stalks and fewer nodes with inflorescences on the main stem, but no other abnormal morphological changes were observed.
Flower malformation was induced when shoots were exposed to high temperature around 30 Apr. when stamen initiation in the terminal floret was occurring. Anatomical studies revealed that the flower malformation was related to an abnormally extended period of transformation of stamens to petaloid structures prior to anthesis. Meristematic activities of the stamen primordia were prolonged after an exposure to high temperature at this stage of floret formation. Consequently, cluster-like petaloid stamens formed around the meristematic tissue that resulted in increased number of petals. Malformed flowers occurred more frequently in cultivars and vegetative lines which require longer durations of chilling.
These results show that the exposure to high temperature neutralizes the chilling effects for reproductive growth and induces the formation of rosettes. Both rosettes and malformed flowers may be expressions of the transition from the reproductive growth (anther) to a vegetative one (petal) at the meristematic level, as a result of exposure to high temperature.