ETHYLENE EVOLUTION AND AMMONIUM ACCUMULATION BY NUTRIENT-STRESSED TOMATO PLANTS

Environmentally stressed plants frequently have elevated rates of ethylene evolution and high accumulation of free ammonium by their foliage. The objective of this study was to investigate ethylene evolution and ammonium accumulation by nutrient-deficient and ammonium-stressed tomato plants (Lycopersicon esculentum Mill. 'Heinz 1350' and neglecta-1) grown in a greenhouse. In soil culture, 'Heinz 1350' was more sensitive to ammonium toxicity and had higher ethylene evolution than neglecta-1. High ethylene evolution corresponded with appearance of ammonium toxicity symptoms in both lines. In sand culture, 'Heinz 1350' and neglecta-1 grown with K, Ca, or Mg deficiency in NO3--based nutrient solutions had higher ammonium accumulation and higher ethylene evolution than plants grown with complete nutrition. P-deficient plants had elevated ammonium accumulation but low ethylene evolution. Plants grown on NH4+-based nutrition with pH buffering by CaCO3 had lower ethylene evolution and lower ammonium accumulation than plants grown in unbuffered solutions but had higher values than plants grown with NO3--based nutrition. Adequate K nutrition suppressed ethylene evolution and ammonium accumulation for all plants regardless of nitrogen regimes. Ammonium accumulation and ethylene biosynthesis in plants appear to be related processes. They appear to be indicators of stress and may have roles in development of symptoms of nutritional stresses.