Nondestructive FTIR monitoring of leaf senescence and elicitin-induced changes in plant leaves

Abstract

The applicability of the FTIR attenuated total reflectance technique for in situ monitoring of plant physiological processes such as leaf senescence and aging has been examined. Difference spectra obtained by subtracting the spectrum of the young plant leaf from that of the older one revealed positive bands at 1650-1500 cm(-1), indicating a higher relative concentration of phenolics in the older leaves of both black cherry and sweet pepper bush leaves. Prolonged physiological stress of tobacco leaves exhibited a progressive time-dependent increase of the absorbance at around 3475 cm(-1), corresponding to hydroxyl functional groups. Absorption changes were also observed between 1650 and 1500 cm(-1), which are likely to correspond to phenolics. The characteristic changes of the FTIR absorbance spectra resulting from physiological and induced aging were detected also as a response to treatment with a recombinant alpha-elicitin, cinnamomin. This allowed the first quantification of the biological activity of a recombinant elicitin using a spectroscopic method. We suggest that FTIR spectroscopy provides important information about physiological events occurring in plant tissue in vivo, and it could be useful for the in situ characterization of the plant responsiveness to fungal toxins such as elicitins.