Changes in spinach thylakoid activity due to nitrite ions

The introduction of nitrite ions into the bathing medium of broken spinach chloroplasts causes changes in the properties of these organelles which depend on the concentration of nitrite and the time of exposure. In the presence of 1 mM nitrite, there is an inhibition of the rate of oxygen evolution and an increase in fluorescence emission which suggests a site for nitrite inhibition between the two photosystems. When 5 mM nitrite is present for times longer than 10 minutes, there is a decrease in the PS2 partial reaction rate as indicated by the oxygen burst, an increase in the PS1 partial reaction rate, a decrease in fluorescence emission and an increase in the fluorescence emitted at 729 nm compared with that at 693 nm observed at - 176°C. These changes are consistent with an increase in the proportion of absorbed light energy reaching PS1 caused by prolonged exposure to a sufficient concentration of nitrite ions in the light.