INDUCTION OF CHLOROPHYLL-A FLUORESCENCE IN CLOVER LEAVES GROWN AT VARYING NITROGEN SUPPLY AND IRRADIANCE LEVELS

The influence of nitrogen supply on the characteristics of induction c urves of chlorophyll a fluorescence in clover leaves was investigated. The effect of irradiance level on the relative magnitudes of the P an d M peaks of the fluorescence induction curve was more pronounced in n itrogen-deficient plants. The characteristics of the secondary peak (M 2) of the fluorescence induction curve were most affected by the nitro gen supply level. in nitrogen-deficient plants, this peak appeared and disappeared earlier (in plants grown at 30 or 70 W/m(2)) or had a low er magnitude (in plants grown at 100 W/m(2)). It is concluded that the appearance of the M2 peak on induction curves of chlorophyll fluoresc ence from clover leaves is due to a change in the energy metabolism of chloroplasts after the beginning of the operation of the glutamine sy nthetase-glutamate synthase cycle.