Table II.

Effect of inhibitors of protein kinases or protein phosphatases on Al-induced malate efflux from root apexes of Al-resistant wheat (cv Atlas)

Treatment	Malate Efflux
	nmol apex−1 30 min−1
Control	0.84 ± 0.02
Protein kinase inhibitors:
50 μm KN-62	0.84 ± 0.04
10 μm Calphostin C	0.91 ± 0.00
10 μm Chelerythrine	0.90 ± 0.02
10 μm Staurosporine	0.53 ± 0.04
10 μm K-252a	0.07 ± 0.03
Protein phosphatase inhibitors:
10 μm Cyclosporin A	0.89 ± 0.03
10 μm Microsystin-LR	0.93 ± 0.02
1 μm Calyculin A	0.83 ± 0.03
1 μm Okadaic acid	0.64 ± 0.05

Excised root apexes were pretreated with 200 μm CaCl₂ solution (Ca solution) containing or not containing either type of inhibitor and then exposed to the Ca solution containing 200 μm Al (pH 4.2) (Ca⁺Al solution). The highest concentration of each inhibitor tested in the experiment is indicated. Dimethyl sulfoxide concentration in the Ca solution was less than 1%, and dimethyl sulfoxide at this concentration did not inhibit Al-induced malate efflux. After the pretreatment, root apexes were rinsed three times with the Ca solution to remove excess inhibitor. Periods of pretreatment and treatment were 30 min each. Values are means ± se (n = 3).