Auxin induces an increase of Ca2+ concentration in the cytosol of wheat leaf protoplasts.
Auxin addition to protoplasts isolated from leaves of 6-day-old wheat seedlings (Triticum aestivum L. cv. Kadett) induced a rapid increase in the cytosolic calcium concentration [Ca2+]cyt. The shifts in [Ca2+]cyt were detected by use of fluorescence microscopy in single protoplasts loaded with the calcium binding tetra[acetoxymethyl]ester of the fluorescent dye, Fura 2. Addition of the synthetic auxin naphthyl acetic acid, 1-NAA, induced an increase in [Ca2+]cyt within 5-10s, while the physiologically non-active analogue, 2-NAA, did not. The amplitude of calcium increase depended on the concentration of 1-NAA. Since the process was affected by different concentrations of Ca2+ in the external medium, and since the calcium channel blockers (nifedipine and verapamil) postponed and inhibited the reaction, it is suggested that auxin primarily activates Ca2+-permeable channels in the plasma membrane. In the presence of low external calcium concentration (0.1 mM), 5 mM LiCl almost totally blocked the increase in [Ca2+]cyt, indicating a possible involvement of tonoplast Ca2+-channels in the auxin-induced [Ca2+]cyt shift. Thus, calcium signalling induced by auxin involves both external and internal Ca2+ pools.
Shishova
Maria
M
Department of Plant Physiology and Biochemistry, St. Petersburg State University, 199034 St. Petersburg, Russia.
Lindberg
Sylvia
S
D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D007210:Indoleacetic Acids / Q000494:pharmacology*; D007700:Kinetics; D008856:Microscopy, Fluorescence; D010937:Plant Growth Regulators / Q000494:pharmacology*; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D011523:Protoplasts / Q000187:drug effects / Q000378:metabolism; D014908:Triticum / Q000187:drug effects / Q000378:metabolism*
D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D002118:Calcium