Early signalling events induced by glycine application in protoplasts of Mimosa pudica motor cells

Some amino acids have been shown to be signalling molecules in various developmental and stress processes, besides their roles in plant nutrition. Glycine is absorbed by pulvinar motor cells of Mimosa pudica according to an H⁺-Gly cotransport mechanism and under the control of calcium availability. Noteworthy, glycine triggers early plasma membrane depolarization and H⁺ migration. The unicellular model of protoplasts isolated from pulvini absorbed glycine with characteristics similar to those determined on multicellular motor tissues, considering metabolism regulation, plasma membrane functionality and calcium control. This model allows to observe that a rapid increase of glycine uptake rate occurs in the first 3 min following 10 mM glycine application. Additionally, we monitored a rapid transient increase (within 5-11 s) of the cytoplasmic free calcium ([Ca²⁺]c) measured by cytofluorimetric determination using Indo-1-loaded protoplasts. The low [Ca²⁺]c increase seen in nominally Ca²⁺-free medium and the inhibition of [Ca²⁺]c increase after treatment with channel inhibitors (LaCl₃, nifedipine) argue for a Ca²⁺ mobilization from external stores. This observation emphasized the signalling role of glycine at the plasma membrane site.