Effects of Temperature on Metabolism in Tomato

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Abstract
300 tomato plants, previously given a minus-N nutrient solution for 6 weeks, were grown in sand culture in 3 glass inclosed chambers whose humidity was maintained at 85% in all cases but whose temps. were ([plus or minus]1.5[degree]) 55[degree], 70[degree], and 95[degree]F, respectively. Sunlight and CO2 supply varied but at any given time were the same for each temp. treatment. Half of the plants at each temp. received a complete nutrient solution, the others received a minus-N solution for the period of the experiments. At 55[degree] F carbohydrates accumulated in large quantities. Nitrate was absorbed instantaneously and distributed throughout the plant in 5 hrs. but was synthesized to organic N slowly, as a result of which carbohydrates were high even in nitrate supplied plants. Chlorophyll content was low and chloroplasts poorly developed. Veins and stems were purplish due to anthocyanins and stems were hard and woody with thick cell walls. At 70[degree]F plants lacking an external N supply were not so high in carbohydrates as those at 55[degree] and exhibited symptoms of protein deficiency in less degree. Nitrate absorption was instantaneous and translocation slightly more rapid than at 55[degree] but less rapid than at 95[degree]. Plants were higher in nitrate reducing material and assimilation of nitrate was rapid with resultant lower concentration of carbohydrates in plants receiving nitrate as compared with minus-N plants. However, complete nutrient plants were moderately high in carbohydrates, contained abundant elaborated N, were dark green and succulent, and grew vigorously. At 95[degree] F respiration apparently exceeded CO2 assimilation so that all plants decreased in concentrations of carbohydrates. Accompanying this there was a breaking down of complex proteins to simpler forms of organic N, accelerated growth for a few days, and death. At first nitrate assimilation was extremely high and growth rapid, but after 4-5 days nitrate assimilation practically ceased and nitrate supplied plants grew more slowly than at 70[degree]F. Nitrate supplied plants lost carbohydrates more rapidly and died sooner than minus-N plants. After the first few days chloroplasts disintegrated and the plants became soft, yellowish green and devoid of anthocyanins.