THERMOLUMINESCENCE AS A PROBE OF PHOTOSYSTEM-II IN INTACT LEAVES - NONPHOTOCHEMICAL FLUORESCENCE QUENCHING IN PEAS GROWN IN AN INTERMITTENTLIGHT 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 v ariable fluorescence and a certain capacity for reversible non-photoch emical quenching. It has been suggested that reversible quenching may be caused by pH-dependent release of Ca2+ 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 a round 50 degrees 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 Ca2+ (One and Inoue (1989) Biochimica et Biophysica Act a 973: 443-449). The 50 degrees C band disappears upon dark adaptation . In mature leaves, no significant band is seen at 50 degrees C. It is concluded that, in IML leaves, reversible quenching may be related to the release of Ca2+ from Photosystem II, However, it seems that in th e mature system, under most conditions, such release does not contribu te significantly to quenching.