AMMONIUM NUTRITION ENHANCES CHLOROPHYLL AND GLAUCOUSNESS IN KOHLRABI

Kohlrabi (Brassica oleracea var. gongylodes) plants were grown in the greenhouse under autumn conditions and fertilized either with pellets containing nitrogen as 40% ammonium sulphate and 60% urea or with nutr ient solution containing nitrogen predominantly as nitrate. Plants giv en nitrogen as ammonium ions developed glaucous leaves compared to tho se supplied with nitrate which formed glossy leaves. Ammonium-induced glaucousness was the result of a two-fold increase in the amount of ep icuticular wax and a markedly altered fine structure. Leaves from ammo nium fertilized kohlrabi plants also showed a 21% increase in chloroph yll content together with a reduction in the chlorophyll a:b ratio and decreased ground state fluorescence compared to plants supplied with nitrate. Photosynthesis and stomatal transpiration were unaffected by the form of supplied nitrogen. (C) 1996 Annals of Botany Company