Abstract
We analyzed the contribution of CEF-PSI to the induction of Non-photochemical quenching (NPQ) in tobacco leaves. At CO2-saturated condition, electron flux in PSI (Je(PSI)) continued to increase even after both electron flux in PSII (Je(PSII)) and CO2-evolution rate (V(CO2) ) saturated against light intensity. These results indicated that an electron flow in PSI (CEF-PSI), not related to photosynthetic linear electron flow, occurred. NPQ increased drastically after Je(PSII) saturated, and had a strong, positive relationship with CEF-PSI activity. At light-saturated and 20% O2, lowering partial pressure of CO2 (pCO2) decreased Je(PSI), Je(PSII) and V(CO2), but increased NPQ. The extent in the decrease in Je(PSI) was lower than that in Je(PSII). That is, CEF-PSI was induced at low pCO2. Furthermore, the activity of CEF-PSI also had a strong relationship with NPQ. Therefore, CEF-PSI induced the formation of NPQ under the condition where the regeneration of NADP+ for PSI limited photosynthesis.
