Thermoluminescence as a probe of Photosystem II in intact leaves: Non-photochemical fluorescence quenching in peas grown in an intermittent light regime.

We have measured thermoluminescence (TL) and chlorophyll fluorescence from leaves of peas grown under an intermittent light regime (IML) and followed changes in those leaves during greening. IML peas show low variable fluorescence and a certain capacity for reversible non-photochemical quenching. It has been suggested that reversible quenching may be caused by pH-dependent release of Ca(2+) from Photosystem II (PS II) (Krieger and Weis (1992) Photosynthetica 27: 89-98). Under conditions in which reversible non-photochemical quenching occurs, a TL band at around 50 °C is observed, in the presence of DCMU, in IML leaves. A band in this temperature range has previously been observed in PS II depleted of Ca(2+) (Ono and Inoue (1989) Biochimica et Biophysica Acta 973: 443-449). The 50 °C band disappears upon dark adaptation. In mature leaves, no significant band is seen at 50 °C. It is concluded that, in IML leaves, reversible quenching may be related to the release of Ca(2+) from Photosystem II. However, it seems that in the mature system, under most conditions, such release does not contribute significantly to quenching.