Corm and Shoot Development of Freesia hybrida ‘Super Emerald Mixture’ as Related to Endogenous Abscisic Acid and Indoleacetic Acid Levels in the Developing Corm1

Abstract

Corm, shoot, and flower development in seed grown Freesia hybrida Bailey cv. Super Emerald Mixture were compared with levels of endogenous indoleacetic acid (IAA), abscisic acid (ABA) and conjugated ABA (conj-ABA) in the developing corm tissue. Lowering the forcing temperature to below 15°C stimulated floral initiation and corm filling. IAA levels decreased midway through corm filling in 1977 whereas in 1978 the decrease was not statistically significant. During the period of rapid corm filling, ABA levels increased as the temperature decreased below 15° suggesting an association between temperature, corm filling, and ABA.

Localization of Endogenous Growth Substances in Freesia hybrida ‘Moya’ Corms Before and After a Heat Treatment1

“…In contrast to Rehnstrom's findings, we found that IAA was present in whole freesia corms; at 2° the level decreased from 10 ng/g fresh weight to 3 ng over a 13 week period (5). IAA decreased at 30° storage from 10 to 4 ng/g fresh weight over a 13 week period while the highest IAA levels were found in newly forming or pupating corms at 13° (4,5). In gladiolus, a close relative of freesia, corms of developing plants contained auxin which disappeared at the end of the growing season and reappeared after 2 months of storage at room temperature (22).…”

“…The level of whole corm ABA decreased during 13 weeks of 30°C storage and did not correlate well with the degree of dormancy in freesia corms (5). Rather, ABA appeared to have a promotive role in new corm formation (4,5). Aung and De Hertog (2), working with tulip bulbs, reported that total ABA content increased 2 to 4-fold, depending on the cultivar, during the course of the several temperature regimes.…”

“…The physiology and biochemistery of temperature regulation of the growth and development of bulbs, tubers, or corms during their various morphological changes is still only theoretical (18). Earlier work has reported the presence of endogenous growth substances and possible dormancy and growth control (3,4,6,19,24,25). Rehnstrom (19) using bioassays, showed no auxin (IAAlike growth substance) or inhibitors present in Freesia hybrida corms held at 5°C, slight amounts of auxin and inhibitors present after 2 to 3 weeks storage at 10°, and increased auxin levels in the apical and basal zones as the length of storage at 30° increased.…”