Plants are essential organisms as they provide oxygen for the biosphere and food for the herbivories as well as subsequent food chains. When the importance of plant kingdom was recognized soon many experimental efforts followed, especially on plants relevant due to economic reasons (maize, tomato, rice, pea) striving to understand how plants function. It quite soon become clear that since land plants are multicellular organisms the commutation between individual cells has to be coordinated. Already Charles Darwin recognized that fact analyzing the directional growth of grass coleoptiles towards light noticing that places as photo-sensing (apex) and differential growth (cells of hypocotyl below the apex) are spatially separated yet there has to be a communication between those tissues to enable the phototropic response. It was later discovered that auxin is responsible for the cellular differential growth during bending and that the hormone is naturally occurring in the plant body as indol-3-acetic acid (IAA) that resembles tryptophan in chemical structure. Latter it became clear that the differential relocation of auxin that coordinates the tropic differential growth is facilitated by auxin translocators and that PIN auxin efflux carriers were critically important in formation of the developmentally crucial IAA accumulation patterns. Both aspects of the scientific area outlined above deserve a more intensive investigation: the biochemical details of PIN facilitated auxin transport are not well known nor is the integration of signals that enables the tropic response of plants a process in which auxin transport plays an important role.