INORGANIC NITROGEN NUTRITION OF THE SEEDLINGS OF THE ORCHID, CATTLEYA

Abstract

When grown in vitro in a medium containing NH4NO3 as the sole source of nitrogen, seeds ro the orchid, Cattleya (C. labiata ‘Wonder’ X C. labiata ‘Treasure'), germinated readily and proceeded to form small plantlets. Development of the embryos was accompanied by an increase in their total nitrogen and a decline in the percent dry weight. Growth responses of the seedlings in other ammonium salts like (NH4)2SO4, (NH4)2HPO4, NH4Cl, ammonium acetate and ammonium oxalate were similar to that in NH4NO3. However, when grown in a medium containing NaNO3, development of the seedlings was drastically inhibited; KNO3, Ca(NO3)2, KNO2 and NaNO2 also were poor nitrogen sources. Attempts to grow the seedlings in NaNO3 by changing the pH or by addition of kinetin, molybdenum or ascorbic acid as supplements were completely unsuccessful. When seedlings growing in NH4NO3 for varying periods were transferred to NaNO3, it was found that those plants allowed to grow for 60 or more days in NH4NO3 could resume normal growth thereafter in NaNO3. Determination of the nitrate reductase activity in seedlings of different ages grown in NaNO3, after NH4NO3, showed that the ability of the seedlings to assimilate inorganic nitrogen was paralleled by the appearance of the enzyme.