Ethylene Evolution by Tomato Plants Under Stress of Ammonium Toxicity

Abstract
Tomato (Lycopersicon esculentum Mill. cv. Heinz 1350) plants grown in soil with N supplied from (NH4)2SO4 solutions showed a morphological disorder characterized by leaf epinasty. The development of this disorder was accompanied by an increase in the rate of ethylene evolution from whole plants. Ethylene evolution from plants supplied with 0.04 m NH4-N increased to a peak of 112 nl·g−1·hr−1 at ≈2 weeks following the start of fertilization compared to 11 nl·g−1·hr−1 from plants supplied with 0.04 m NO3-N. Fertilization with KC1 in molar equivalency to the supply of NH4-N prevented epinasty and the burst in ethylene evolution. Ethylene evolution from plants of the yellow-green-5 and neglecta-1 mutants did not increase in response to NH4-N fertilization. Potassium concentrations in shoots of ‘Heinz 1350% yellow-green- 5, and neglecta-1 were 2.10, 2.53, and 3.22% (dry weight), respectively, if plants were supplied with NH4-N and no additional K, suggesting that tolerance to NH4 toxicity may be explained in part by differences in K accumulation.

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