ABSTRACT
In nature crops seldom grow under ideal nutritional conditions to give potential growth and yield. Often crops face deficiency or unavailability of one or more nutrient element(s). Ethylene production by the ammonium deficiency-stressed tomato plants greatly exceeds that of unstressed plants on nitrate nutrition. Potassium (K) deficiency causes an additional increment in ethylene evolution over that of ammonium-grown plants with full K nutrition. Phosphorus (P) deficiency decreases the gravitropic sensitivity of both basal roots and tap roots of common bean, soybean and peas. Root hairs are very important in the acquisition of soil resources that move only small distances by diffusion, such as P, K and the micronutrients, by extending the ethylene radius of root uptake. Changes in root elongation of young barley and oat seedlings in response to copper toxicity result from inhibition of biosynthesis or action of ethylene, although the copper treatment first stimulates ethylene production.
