Effect of Zinc Sulfate and Boric Acid on the Hormonal Status of Potato Plants in Relation to Tuberization

Potato (Solanum tuberosum L.) plants were grown in a greenhouse using zinc- and boron-deficient soil. The effects of seed-tuber treatment with 3 mM zinc sulfate and 8 mM boric acid on the content and ratio of phytohormones in the leaves and mature tubers, the indices of photosynthetic activity, the rate and NaF-sensitivity of respiration, and the tuber growth were studied. Zinc-sulfate treatment shifted the hormonal balance toward a substantial increase in the cytokinin content and the cytokinin/ABA ratio, as well as a decrease in the IAA/cytokinin ratio. Boric-acid treatment resulted in an increase in the IAA content and IAA/cytokinin ratio. Zinc-sulfate treatment abolished the apical dominance and increased the tuber weight due to their increased number and the number of phellem (cork) cell layers. Boric-acid treatment increased cell diameter in the tuber perimedullary zone; an increase in tuber weight per plant was related to tuber growth. A relationship between changes in the plant hormonal status induced by zinc-sulfate and boric-acid treatments and the activity of physiological processes is discussed.