In vivo Chlorophyll Fluorescence Spectroscopy in Kiwi Fruit

MENDES NOVO, J.; IRIEL, A.; LAGORIO, M. G.

Mendoza

Congreso; 21st Inter American Photochemical Society Conference; 2011

American Chemical Society

Kiwi fruit displays variable fluorescence emission from chlorophylls, similar to that observed from leaves. This behaviour is related to photosynthetic activity of tissues and its analysis has been lately used in the non-destructive diagnosis of plant health and fruit ripening. Using a pulse modulated fluorometer Hansatech FMS1, the maximum quantum efficiency of PSII photochemistry (Fv/Fm), the quantum efficiency of photosystem II (F PSII), and the photochemical and non-photochemical quenching coefficients (qP and qNP respectively) were determined for the whole fruit as a function of the storage time. Experiments were performed at both 4ºC and room temperature and the total storage time was 25 days. In the studied period of time, Fv/Fm slightly decreased for the chilled fruits while it diminished around 60 % for room-temperature kiwis. The parameter F PSII decreased appreciably for both storage conditions (50% and 100% respectively). The quenching coefficients also decreased in both cases but showing high dispersion in measurements. The most sensitive parameter related to the storage time was F PSII. Under low photon flux irradiation at 460 nm, the whole kiwi fruit showed a non-variable emission showing peaks in the red and far red regions. This fluorescence was also detected for the flesh but it was absent in the juice. The fluorescence peaks ratio (Fred/F far-red) was calculated from fluorescence spectra recorded with a PTI Quanta Master Steady-state fluorometer. This ratio showed a decrease during storage time but less important than that observed for the case of F PSII. The spectral distribution of fluorescence was studied for the different parts of the fruit finding different values for the fluorescence ratio (Fred/F far-red) in each of them. The observed spectra were corrected for distortions due to light re-absorption processes using physical models. The results were interpreted according the relative contribution of photosystems I and II to the total observed fluorescence and they were compared with the chlorophyll emission for standard leaves. The results obtained from the experiments based on chlorophyll variable-fluorescence allow the development of non-destructive methodologies to infer information about the kiwi state in relation to storage conditions and time. On the other hand, the steady-state experiences led to an exhaustive comprehension of the particular features of chlorophyll fluorescence in Actinidia deliciosa.