Cytokinin increases intracellular Ca 2+ in Funaria: Detection with indo-1

Abstract

Changes in intracellular [Ca 2+] ([Ca 2+] i) after cytokinin-treatment in protonema cells of the moss Funaria hygrometrica have been measured using the pentapotassium salt of indo-1. The extent of dye loading strongly depended on lowering the pH of the incubation medium to 5.0. Exposing dye-loaded cells briefly with Mn 2+ did not quench fluorescence suggesting that the source of fluorescence is from the cytoplasm and not from the cell wall. Indo-1 remains responsive to changes in [Ca 2+] i in Funaria cells. The [Ca 2+] i in quiescent cells (with and without extracellular Ca 2+) is 250 nM, which is within the range of reported [Ca 2+] i of other plant cells. Treatment of cells with extracellular cytokinin in 4 mM Ca 2+ induced a three-fold increase in [Ca 2+] i to 750 nM in target caulonema cells. This increase was not observed in Ca 2+-free medium. These target cells respond to cytokinin treatment by an asymmetrical division, while non-target chloronema cells do not divide. Cytokinin appears to increase [Ca 2+] i by extracellular Ca 2+ uptake. However, non-target chloronema cells and tip cells also respond to cytokinin treatment by increasing [Ca 2+] i. The differential physiological response of these cell types to hormonal stimulation must lie further down the signal transduction chain.