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H+-Coupled Sugar Transporter, an Initiator of Sugar-induced Ca2+-signaling in Plant Cells

Abstract Using Ca2+-dependent photoprotein aequorin-transformed tobacco BY-2 cell suspensions, the sugar-induced increase in cytosolic free Ca2+ concentration ([Ca2+]cyt) was investigated by measuring the luminescence intensity. When 0.5 ᴍ sucrose or some other sugars were fed to the cells, strong and transient luminescence was observed. Salts or sugar analogues didn’t show this effect. In addition, the intensity of sucrose-induced aequorin luminescence was gradually enhanced when cells were exposed to sugar-starvation. This was observed with the concurrent expression of the sucrose/H+ co-transporter, NtSUT1A. The [Ca2+]cyt increase may initiate Ca2+-signaling leading to the expression of genes related to biosynthesis of storage carbohydrates in a sink organ. The sugar-signaling may play an important role in the conversion on nutritional stage of plant tissue, source organ to sink organ.