The aim of the present study was to examine the influence of spectral composition of irradiation (white - WL or white supplemented by blue radiation - WBL) and ozone on chlorophyll content and the optical properties of broccoli leaves (Brassica oleracea var. botrytis cymosa). Broccoli leaves were injured by the ozone dose applied (70 ppb, 6 hours daily) mainly under WBL. Leaf lamina damage was much larger in the outer, physiologically older part than in the inner, physiologically younger part. Therefore, further studies were carried out separately on leaf fragments from the outer(OP) and the inner parts (IP). The spectrophotometric analysis did not reveal significant differences in the chlorophyll content between treatments. The variations in reflectance in the visible region (400-700 nm) were generally not significant with respect to tissue age (OP, IP), ozone fumigation and growth conditions (WBL, WL). Only in plants grown under WBL there was an increase in green reflectance in ozone-treated leaves observed, which indicates a decrease in the chlorophyll content in leaves. Thus, measurements of the optical properties of leaves provide more precise information about changes in the content of chlorophyll than spectrophotometry. Leaves under WBL showed significant differences in reflection within the range 800-1100 nm, which depended on the physiological age of the tissue. For physiologically older tissues, values of reflection were lower than those for physiologically younger tissues. However, under WL conditions, a decrease in reflection within the 800-1100 nm rangę depended only on ozone fumigation. Response of broccoli leaves to spectral composition of irradiation and ozone stress was much higher for irradiation transmission than for reflection. Compared to the control, ozone fumigation of broccoli leaves grown in WBL increased irradiation transmission in OP and IP leaf fragments, both in the 500-700 nm and 750-1100 nm ranges. For plants growing in WL no influence of ozone fumigation on the transmission of irradiation within the visible range was observed. However, fumigation with ozone resulted in a significant decrease in the transmission within the infrared range (750 to 1100 nm). The results indicate the major role of irradiation spectral composition in plant response to ozone stress. The modifications may affect Chl content, leaf temperature and, what is more important, phytochrome-controlled morphogenetic processes.
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