The thermoluminescence 'afterglow' band as a sensitive indicator of abiotic stresses in plants

Single turn-over xenon flashes induce a thermoluminescence (TL) B-band cent red near 35 degrees C. The far-red illumination of leaves at non-freezing t emperatures induces a band peaking at around 45 degrees C (afterglow or AG- band), together with a downshifted B-band peaking between 15 degrees C and 28 degrees C. In control, unfrozen wheat plants, the T-max of the B-band in duced after 30 s far-red light at 0 degrees C was approx. 15-18 degrees C. In maize plants grown under the same conditions, this far-red-induced downs hift was not so strong, since the B-band peaked at 28-30 degrees C. Both a decline in the AG-band and a reversal of the downshift of the B-band were o bserved after short-term freezing in several plant species. There was usual ly a sudden drop in the AG-band below a critical freezing temperature. Howe ver, while in wheat plants a weak TL emission could be seen between 40-50 d egrees C in frozen samples, in cold-sensitive maize plants this was complet ely suppressed and only the B-band could be detected. In cold-hardened whea t plants the temperature at which the AG-band was suppressed was lower than in non-hardened plants. Drought and short-term heat stress also affect the AG-band. As the AG-band was found to be more sensitive to several types of stresses than the B-band, it can be used as a sensitive stress indicator. However, the behaviour of the AG-band depends on several factors (for examp le the age of the leaf, etc.), which must be controlled if different specie s or varieties are to be compared.