ASSESSMENT OF CHILLING INJURY DURING STORAGE - CHLOROPHYLL FLUORESCENCE CHARACTERISTICS OF CHILLING-SUSCEPTIBLE AND TRIAZOLE-INDUCED CHILLING TOLERANT BASIL LEAVES

Chlorophyll (Chi) fluorescence analysis by pulse-amplitude modulation (PAM) measurements was performed to assess the extent of chilling inju ry (CI) in stored sweet basil (Ocimum basilicum L.) leaves. Changes in three photosynthetic characteristics, in relation to visible CT ratin g, were monitored in leaves following modification of their chilling s usceptibility by varying storage temperature and duration in two basil cultivars, or by soil application of triazole. Basil leaves developed severe or moderate visible symptoms of CI after 4 days of storage at 4 or 8 degrees C, respectively, but remained undamaged when stored at 12 degrees C. The chilling-dependent changes obtained in the ratios of variable to maximal fluorescence (F-v/F-m), represented chilling sens itivity rather than membrane damage. The photochemical quenching coeff icient (qP) was unaffected by low temperatures and did not seem to be correlated with CI. On the other hand: changes in the non-photochemica l quenching coefficient (qNP) were positively correlated with the appe arance of visual CI symptoms in leaves of the two cultivars at all sto rage temperatures and durations. Similarly, the chilling-alleviating e ffect of triazole was accompanied by a corresponding reduction in the chilling-induced decrease of qNP. Therefore, qNP may be associated wit h an irreversible transition step in the CI process, which precedes th e appearance of visual symptoms. As such, changes in qNP may provide a suitable, rapid and non-destructive criterion for estimation of chill ing damage in green tissues. (C) 1997 Elsevier Science B.V.