Plant cell elongation growth is an integral process involved in different plant movements (tropisms); it provides the possibility to reach different resources of energy, water and nutrition and is therefore important for metabolism and development. Cell multiple enlargement along the longitudinal axis is commonly accepted to be under the control of the phytohormone auxin. One of the key enzymes involved in elongation is the plasma membrane H ⁺ -ATPase, which is known to acidify the cell wall. Investigation of the role of the proton pump at the plasma membrane was initiated by Prof. Vsevolod V. Polevoi and still is in progress in the group of Prof. Maria F. Shishova at the Department of Plant Physiology and Biochemistry, St. Petersburg State University. Different mechanisms of post-translation regulation of H ⁺ -pump activity are discussed in this review. We also suggest a possible scheme of elongation growth based on the shift in plant cell sensitivity to auxin and on its facility to elongate.