The response of photosystem I to fluctuating light is influenced by leaf nitrogen content in tomato

Abstract

Fluctuating light and nitrogen (N) deficiency can occur synchronously under natural growth conditions. However, little is known about the photosynthetic regulation under fluctuating light in plants grown with N deficiency. In the present study, we examined the effect of N supply on the response of photosystem I (PSI) to fluctuating light in tomato. Plants grown under high N concentration (HN-plants) had higher leaf N content, chlorophyll content and saturating CO2 assimilation rate than plants grown under middle and low N concentrations (MN- and LN-plants). After an abrupt increase in illumination for 10 s, all plants could not generate a sufficient proton gradient (ΔpH). Meanwhile, PSI was over-reduced in HN- and MN-plants but was highly oxidized in LN-plants. In LN-plants, the smallest PSII electron flow avoided an over-reduction of PSI under fluctuating light. After transition from low to high light, CEF gradually increased to the peak in 30 s in HN-plants but rapidly increased to the peak in 10 s in MN-plants. Such delayed activation of CEF in HN-plants accelerated the over-reduction of PSI. After fluctuating light treatment, HN-plants displayed the greatest PSI photoinhibition, followed by MN- and LN-plants. These results indicated that leaf N content significantly affected the response of PSI to fluctuating light in tomato.