Why and What for the Leaves Are Yellow in Autumn? On the Interpretation of Optical Spectra of Senescing Leaves (Acerplatanoides L.)

The reflectance, transmittance and absorption spectra of Acer platanoides leaves were recorded in the progress of full-term autumn senescence and compared with absorbance spectra of extracts from, and pigment contents in, these leaves. The observed changes in leaf spectra and development of intensive yellow color of the leaves are considered as related to the changes in the light depth penetration in the photosynthetic tissues accompanying chlorophyll breakdown. It is suggested that carotenoids, serving as effective light traps (in spite on their relatively low concentrations), are able to provide protection against harmful effects of blue-light irradiation; it can explain the physiological significance of their retention in leaves up to terminal stages of the senescence process.