Low Nitrogen Nutrients Activate the Cyclic Electron Flow around PSI in Rice Leaves.

Abstract

We characterized the response of cyclic electron flow around PSI (CEF-PSI) to low-nitrogen nutrient conditions using rice plants. Rice plants were hydroponically cultured with the two level nitrogen concentration (MN, 1 mM NH4NO3; LN, 0.3 mM) under high (HL) and low light (LL) intensities. Both Photosynthetic linear electron flow (LEF) and the electron flux in PSI were evaluated from both the quantum yields of PSII (QY(PSII)) and PSI (QY(PSI)), respectively. The ratio of QY(PSI) to QY(PSII) in both HL- and LL-plants increased in response to LN-conditions. These results indicated that the photosynthesis-limited conditions at LN induced the activity of CEF-PSI. We could not detect any difference of QY(PSII) at lower light intensities in all rice plants. However, QY(PSI) in LN-plants were larger than those in MN-plants. These lowered QY(PSI) were activated by the pre-illumination to their leaves. These results showed that low-nitrogen nutrients activated PSI and its enhancement contributed to the activation of CEF-PSI. Activation mechanism of CEF-PSI will be discussed.