In Pea Thylakoids, a Special Thermoluminescence Band Was Observed at Low Temperature after Photoinhibitory Treatments Performed under Aerobic Conditions, either in vivo (in Leaf) or in vitro

Characteristics o f thermoluminescence (TL) glow curves were studied in thylakoids isolated from pea leaves after an exposure to very high light in the TL device. The inhibition o f photo­ synthesis was detected both as decreases o f oxygen evolution rates and o f variable fluores­ cence. In another more classical experiment, leaves were exposed to high light at low tempera­ ture (5 °C) for 4 h and recovery o f normal PS II characteristics were followed during a 20 h time period under low light at 20 °C. TL study was performed on thylakoids isolated from these leaves. Charging o f bands was performed by an illumination at low temperature ( 8 0 °C). Illumination at low temperature ( 8 0 °C) induces 2 types o f TL bands called Z variable (Zv) band peaking at about —70 °C and a classical B band peaking at 35 °C. B band is ascribed to recombination in pairs S2/3QB", whereas the origin o f Zv bands remains unclear. Modified Zv bands, with flat shape and presenting a large part resistant to ethanol, were evidenced after some minutes o f dark adaptation, both in light-exposed thylakoids and in thylakoids isolated from photoinhibited leaves. This ethanol resistant part in Zv band was only induced by photo­ inhibitory treatment performed under aerobic conditions (2 1 % 0 2 in media), both in vitro and in vivo; thus, the appearance o f the special Zv band would be related to an oxidative process accompanying photoinhibition. B bands presented reduced sizes and a shift o f peak maximum o f about 5 °C after some minutes o f dark adaptation. In vivo, the recovery o f a high PS II activ­ ity and o f B bands displaying normal characteristics occurs parallely to reappearance o f Zv bands with normal shape and with a vestigial ethanol resistant band.