EFFECTS OF CALCIUM DEFICIENCY ON NITRATE ABSORPTION AND ON METABOLISM IN TOMATO

Abstract

The upper parts of the tops of Ca-deficient tomato plants were yellow and the lower leaves and stems were fairly green. (In a deficiency of N, P, or K respectively, the lower portion of the plant is yellowish, but the upper leaves and stem remain green.) The roots were characteristically short, bulbous and brown at the tips, with sloughing off of cells further back. Ca-deficient tomato plants under the seasonal light conditions of the greenhouse were practically unable to absorb or assimilate nitrates although they absorbed Ca instantly. The plants which lacked Ca accumulated carbohydrates in large quantities, apparently because absorption and assimilation of nitrates did not take place. Translocation of sugars and digestion of starch took place freely. Nearly 100% of the Ca of fresh tissue of the Ca-deficient plants was water-insoluble and most of it was located in older tissues of roots and tops. (In a deficiency of N, P, or K, respectively, the highest concentration of the deficient elements is in young embryonic tissues.) In Ca-deficient tomato plants, utilization of Ca oxalate and re-utilization of combined Ca took place, but so slowly that root and stem tips died while there were yet heavy deposits of Ca oxalate and a high concentration of combined Ca in older tissues. In Ca-deficient plants that were shaded or placed in continuous darkness for several days, there was a decrease in carbohydrates, associated with proteolysis and a noticeable increase in uncombined Ca and a diminished concentration of combined Ca. Accompanying proteolysis and increase in uncombined Ca there was rapid formation of new stem tissue and absorption of nitrates, even though there was no external supply of Ca available. Darkness treatment of Ca-deficient plants, and shift from minus- to plus-Ca nutrient, are apparently in certain respects similar in principle and effect. In both cases there is made available uncombined Ca for combination with newly formed proteins or other materials. A supply of amino acids for formation of new proteins of meristems is likewise available in both instances; in the Ca-deficient plants in darkness, through proteolysis, and in the plants newly supplied with Ca, through nitrate assimilation.