Aluminum as a specific inhibitor of plant TPC1 Ca2+ channels.
In plant cells, Al ion plays dual roles as an inducer and an inhibitor of Ca(2+) influx depending on the concentration. Here, the effects of Al on Ca(2+) signaling were assessed in tobacco BY-2 cells expressing aequorin and a putative plant Ca(2+) channel from Arabidopsis thaliana, AtTPC1 (two-pore channel 1). In wild-type cells (expressing only aequorin), Al treatment induced the generation of superoxide, and Ca(2+) influx was secondarily induced by superoxide. Higher Al concentrations inhibited the Al-stimulated and superoxide-mediated Ca(2+) influx, indicating that Ca(2+) channels responsive to reactive oxygen species (ROS) are blocked by high concentration of Al. H(2)O(2)-induced Ca(2+) influx was also inhibited by Al. Thus, inhibitory action of Al against ROS-induced Ca(2+) influx was confirmed. Similarly, known Ca(2+) channel blockers such as ions of La and Gd inhibited the H(2)O(2)-induced Ca(2+) influx. While La also inhibited the hypoosmotically induced Ca(2+) influx, Al showed no inhibitory effect against the hypoosmotic Ca(2+) influx. The effects of Al and La on Ca(2+) influx were also tested in the cell line overexpressing AtTPC1 and the cell line AtTPC1-dependently cosuppressing the endogenous TPC1 equivalents. Notably, responsiveness to H(2)O(2) was lost in the cosuppression cell line, thus TPC1 channels are required for ROS-responsive Ca(2+) influx. Data also suggested that hypoosmotic shock induces TPC1-independent Ca(2+) influx and Al shows no inhibitory action against the TPC1-independent event. In addition, AtTPC1 overexpression resulted in a marked increase in Al-sensitive Ca(2+) influx, indicating that TPC1 channels participate in osmotic Ca(2+) influx only when overexpressed. We concluded that members of TPC1 channel family are the only ROS-responsive Ca(2+) channels and are the possible targets of Al-dependent inhibition.
Kawano
Tomonori
T
Graduate School of Environmental Engineering, The University of Kitakyushu, Kitakyushu 808-0135, Japan. kawanotom@env.kitakyu-u.ac.jp <kawanotom@env.kitakyu-u.ac.jp>
Kadono
Takashi
T
Fumoto
Katsumi
K
Lapeyrie
Frédéric
F
Kuse
Masaki
M
Isobe
Minoru
M
Furuichi
Takuya
T
Muto
Shoshi
S
D000331:Aequorin / Q000235:genetics / Q000378:metabolism; D000535:Aluminum / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology*; D002460:Cell Line; D006861:Hydrogen Peroxide / Q000378:metabolism; D007811:Lanthanum / Q000378:metabolism; D009997:Osmotic Pressure; D016877:Oxidants / Q000378:metabolism; D030821:Plants, Genetically Modified; D017433:Protein Structure, Secondary; D017382:Reactive Oxygen Species / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D014026:Nicotiana / Q000166:cytology* / Q000378:metabolism; D000097903:Two-Pore Channels
D000331:Aequorin; D000535:Aluminum; D029681:Arabidopsis Proteins; D002118:Calcium; D015220:Calcium Channels; D006861:Hydrogen Peroxide; D007811:Lanthanum; D016877:Oxidants; D017382:Reactive Oxygen Species; D011993:Recombinant Fusion Proteins; D013481:Superoxides; C498240:TPC1 protein, Arabidopsis; D000097903:Two-Pore Channels