The role of ionic calcium in the gravitropic response of a creeping chrysanthemum cultivar
2011
Zhang, Sh | Chen, S. | Chen, F. | Jiang, B.
The stem of the creeping Chrysanthemum morifolium Ramat. cultivar ‘Yuhuajinhua’ responds to a gravitational stimulus by bending. Most of the calcium ion (Ca2+) present in the stem cells was concentrated in the cell walls, intercellular space, and vacuoles, with very little in the cytoplasm. An investigation of the effects of supplying exogenous Ca2+ or the Ca2+ chelator EGTA on the creeping habit and the level of endogenous IAA showed that, for at least 60 min after gravistimulation was initiated, the level of Ca2+ present in the epidermis cell walls on the lower side of the stem was maintained at a higher level than in those on the upper side. In the endodermis cells, most of the Ca2+ was located in the intercellular space, cell walls, and throughout the vacuole, with only little within the cytoplasm. Endodermis cell Ca2+ responded rapidly (within 5 min) to gravistimulation. The level of Ca2+ continued to increase within the cytoplasm for at least 30 min into the period of gravistimulation. Exogenously applied calcium chloride (CaCl2) accentuated gravity-induced bending and the IAA concentration differed between the upper and the lower sides of the gravistimulated bent stem, whereas EGTA decreased these effects. Ca2+ appears to play an important role in the gravitropism of the ‘Yuhuajinhua’ creeping stem, not only by changing its distribution in the epidermis cell walls and the endodermis cytoplasm, but also by regulating IAA difference between the upper and lower sides of the creeping stem.
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