REGULATION OF THE GRAVITROPIC RESPONSE OF CUT ORNITHOGALUM ‘NOVA’ SPIKES DURING STORAGE AND TRANSPORT IN HORIZONTAL POSITION

Ornithogalum ‘Nova’ flowers have 50–100 cm long and 0.7–1.0 cm thick growing spikes that show a rapid gravitropic response when placed horizontally, thereby manifesting a serious problem during their postharvest handling.
The possible involvement of Ca²⁺ as a second messenger in shoot gravitropism leading to the auxin-induced and ethylene-mediated bending response, was studied through application of various calcium-related agents and ethylene inhibitors.
The gravitropic bending of Ornithogalum spikes following transport simulation was significantly inhibited by application of Ca²⁺ chelators (EDTA, EGTA, CDTA, BAPTA), while the Ca²⁺ -channel blocker LaCl₃ had no effect.
Conversely, application of CaCl₂ Ornithogalum spikes, increased the number of bending flower stalks, and markedly decreased their angle of curvature below 90°. The efficiency of the chelators tested was positively correlated with their specific affinity for Ca²⁺ (BAPTA>CDTA>EGTA>EDTA). Besides being the most efficient chelator in inhibiting bending, BAPTA did not harm flower quality, and retained high fresh weight and chlorophyll levels of florets and bracts during vase life.
The gravitropic bending of Ornithogalum spikes was also retarded by the inhibitor of ethylene action, 2,5-norbornadiene, but was not affected by ethylene synthesis inhibitors.

Longitudinally halved stem sections, cut from gravistimulated spikes, produced significantly higher amounts of ethylene, ACC and MACC compared with vertical controls, with the extra production arising exclusively from the lower half of the stem.
CDTA and EGTA pretreatment completely abolished this gravity-induced ethylene gradient across the stem, thereby leading to a significant reduction of the curvature.
Since the ethylene asymmetry may reflect an asymmetric distribution of auxin across the stem, we have further examined whether cytosolic Ca²⁺ is involved in auxin-induced ethylene production.
Exogenous IAA significantly stimulated ethylene production rates of Ornithogalum stem sections.
This IAA-enhanced production of ethylene was significantly inhibited in stem sections excised from EGTA or CDTA-treated spikes, and the inhibitory effect of CDTA was more pronounced.
This indicates that Ca²⁺ may regulate the auxin-induced production of ethylene which mediates the gravitropic response.

VII International Symposium on Flowerbulbs

S. Philosoph-Hadas, S. Meir, I. Rosenberger, A.H. Halevy

https://doi.org/10.17660/ActaHortic.1997.430.63