| Abstract: | Changes of PS II chlorophyll fluorescence of Dunaliella salinawere used to study the effect of micromolar concentrations ofN-nutrients (nitrate, nitrite and ammonia) on photosyntheticelectron flow. The responses were evoked by changes in lightintensity which were controlled by a special protocol. Thisenabled the splitting of the overall response into individualcomponents by curve fitting and the assignment of these componentsto particular reactions of the photosynthetic apparatus. Byvirtue of a comparison with simultaneously measured changesin transmission at 532 ran, the identification could be madeof the component which is related to redox changes of the acceptorpool of PS I. The time-constant related to this acceptor pool was found toincrease by a factor of up to 5 after the addition of N-nutrients.The results indicate that the addition of N-nutrients increasesthe acceptor pool of PS I. The relationship between nutrientconcentration and effect is not consistent. In contrast to theelectron flow to the Calvin cycle, the electron flow to nitrogenassimilation is not related to a strong consumption of ATP.Thus, it gives rise to an increase in the transthylakoid pHgradient. The expected increase in the kinetic component ofchlorophyll fluorescence related to thylakoid energization isobserved after the addition of nitrate. Key words: Chlorophyll fluorescence, noise, N-nutrient metabolism, time-constants, thylakoid energization |
