LIGHT TRANSMISSION INTO APPLE FRUIT AND LEAVES

Light transmission into tissue of fruit or leaves of apple (Malus pumila Mill.) cultivars 'Golden Delicious', 'Gloster' and 'Cox's Orange Pippin' was studied both quantitatively and qualitatively. For comparative purposes, fruit or leaf was exposed to a constant photosynthetically active radiation (PAR) of 1750-mu-mol m-2 s-1. Under these conditions, transmission of PAR into the inner tissues of apple fruit ranged between 0.04 and 8.4-mu-mol m-2 s-1, dependent on development stage, cultivar and position of the apple tissue relative to the light source. Parenchyma of apple fruit transmitted 1.5-2% of the incident PAR 1.5 mm-1 fruit tissue. Peel of apple fruit transmitted 1-3% of incident PAR at 400 nm, increasing to 10-12% at 850 nm. Whole apple leaves transmitted up to 2%, whereas an upper epidermis and mesophyll layer transmitted up to 7% of incident PAR. With green fruit, transmission and action spectra were dominated by chlorophyll absorption at 678 nm, whereas apple fruit with red or yellow peel additionally absorbed at 480 nm.