ABSTRACT

The study of the effects of light intensity and N level on RuDBC-ase, NAR and photosynthetic activities in citrus leaves was conducted on nine-month old orange seedlings (Citrus sinensis cv. ‘Pineapple’) grown in acid-washed quartz sand in plastic pots under greenhouse conditions at a thermoperiod of 28/20° C day and night, respectively. The seedlings were exposed for six weeks to 16 h photoperiod at light insensity of 600 and 200 umol/m’Vsec-1. Photosynthetically active radiation (PAR) was supplied by metalare lamps (500-620 nm). Seedlings received a complete nutrient solution differing only in N level which was supplied as nitrate. The data indicate that N is more essential for RuBBC-ase and NAR activities, and that high light is not necessary essential for RuBPC-ase activity. Light had an indirect effect on protein systhesis. High N level induced high N level and the synthesis of more protein in the leaves than low N level. Both photosynthesis and chlorophyll content followed the same pattern. They were more related to light regime than N level. The importance of providing the appropriate levels of light and nitrogen to fruit trees in relation to quality produce has been discussed.