Some Effects of Zinc Deficiency on the Anatomy of the Tomato

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Abstract
1. Tomato seedlings of the Rutgers variety were grown with drip-culture solutions in which the concentration of zinc was varied: 0.05 (controls), 0.005, 0.0005 p.p.m., and no zinc at all. At harvest, 1 month from the beginning of the experiment, their growth was proportional to the amount of zinc received. The low-zinc and minus-zinc plants showed definite symptoms of zinc deficiency. One plant from each series was selected for histological study. 2. Extreme zinc deficiency resulted in a reduction or, in the total absence of zinc, a complete cessation of meristematic activity in the root tips and cambium, in necrosis of leaf tissue, and in the precocious maturation of tissues. This was particularly apparent in the root tips, where both xylem and endodermis matured just a short distance from the promeristem. In the roots of minus-zinc plants small but definite tumors, similar to those formed on roots exposed to low concentrations of certain growth-regulating substances, developed a short distance behind the growing tips. 3. Zinc deficiency appeared to have less effect on the primary tissues than on the secondary development of the tomato plant. The fundamental structure of cortex, stele, and pith was quite similar in older stem tissues of the several series, though the higher levels of zinc brought about cell divisions in the cortex that were rare or lacking in those plants receiving little or no zinc. There was relatively little difference in these tissues in the younger parts of the stem. Secondary growth was noticeably retarded in low-zinc plants.