Preharvest Spraying of CaCl2 Alleviates the Scape Bending of Gerbera ‘Harmony’ Flowers by Strengthening the Pectin Crosslinks through Ca2+ Bonds

Abstract

Scape bending is the primary cause shortening the vase life of cut gerbera flowers (Gerbera jamesonii ‘Harmony’). A previous study showed that this bending is closely related to the scape hardness, which is attributed to cell wall rigidity maintained by calcium ion bonds. In this experiment, the developing gerbera scape was sprayed with 0.5 and 1% calcium chloride to determine whether exogenous calcium directly influences scape hardness and whether it is related to pectin crosslinks. The calcium spray hardened the scape by 12% and efficiently reduced bending, thereby prolonging the vase life of the cut gerbera flowers. A 9% increase in calcium ions (Ca2+) was detected in the CaCl2-treated flowers compared to the control flowers. Additionally, the pectin content increased by up to 14% in the CaCl2-treated flowers as compared to that in the control. Pectins are the main polysaccharides of cell walls that impact plant tissue integrity and rigidity, with calcium ions acting as bonds for pectin crosslinking. Calcium treatment efficiently increased the content of total pectin in the cell walls and slowed the conversion of insoluble pectin (IP) to water-soluble pectin (WSP) during vase life. The results suggest that exogenously applied calcium increases the Ca2+ in cellular tissue and affects the pectin levels, which may aid in increasing the scape hardness by strengthening the calcium–pectin combination in cell walls.