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The degree of Zn^2+ effect on the photosynthetic electron transport and photophosphorylation activities in barley chloroplasts has been tested. Zn^2+ treatment was done in the 2 ways. One was that it was added into the chloroplasts suspensions isolated from the plants grown under the normal Zn^2+ level (10^-6M). The other was that the different concentrations of Zn^2+ was applied in each growth medium. Then, it was not added into the chloroplasts suspensions isolated from the plants. PS Ⅱ activity in both way of the treatments was more severely inhibited than PS Ⅰ by the increment of Zn^2+ concentration. The photophosphorylation activity measured by pH measurement was gradually decreased with the increase of Zn^2+ concentration in both ways, too. However, it was shown that Nm^2+ could be near fully overcome the inhibitory effect of Zn^2+ in PS Ⅱ, and Mg^2+ could also reduce the Zn^2+ inhibition in the photophosphorylation. In the low concentrations of Mg^2+ (3 to 5 × 10 exp(-3)M) in the suspension, Zn^2+ (2× 10 exp(-5)M) could increase the activity of photophosphorylation. As compares to other cations, Zn^2+ caused less inhibitory effect on the photophosphorylation activity than Cu, Cd, but more than Pb and Ni. It may be assumed that a complex from reaction of Zn^2+ and mercaptoethanol was produced and it could reduce the stability of CPI band during SDS-PAGE.
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