<P> The regulation of PIN protein localisation in a cell determines the direction of auxin transport from cell, and concentrated effort of many cells creates peaks of auxin, or auxin maxima (regions having cells with higher auxin--a maximum). Proper and timely auxin maxima within developing roots and shoots are necessary to organise the development of the organ . Surrounding auxin maxima are cells with low auxin troughs, or auxin minima . For example, in the Arabidopsis fruit, auxin minima have been shown to be important for its tissue development . </P> <P> As auxins contribute to organ shaping, they are also fundamentally required for proper development of the plant itself . Without hormonal regulation and organization, plants would be merely proliferating heaps of similar cells . Auxin employment begins in the embryo of the plant, where directional distribution of auxin ushers in subsequent growth and development of primary growth poles, then forms buds of future organs . Next, it helps to coordinate proper development of the arising organs, such as roots, cotyledons and leaves and mediates long distance signals between them, contributing so to the overall architecture of the plant . Throughout the plant's life, auxin helps the plant maintain the polarity of growth, and actually "recognize" where it has its branches (or any organ) connected . </P> <P> An important principle of plant organization based upon auxin distribution is apical dominance, which means the auxin produced by the apical bud (or growing tip) diffuses (and is transported) downwards and inhibits the development of ulterior lateral bud growth, which would otherwise compete with the apical tip for light and nutrients . Removing the apical tip and its suppressively acting auxin allows the lower dormant lateral buds to develop, and the buds between the leaf stalk and stem produce new shoots which compete to become the lead growth . The process is actually quite complex, because auxin transported downwards from the lead shoot tip has to interact with several other plant hormones (such as strigolactones or cytokinins) in the process on various positions along the growth axis in plant body to achieve this phenomenon . This plant behavior is used in pruning by horticulturists . </P> <P> Finally, the sum of auxin arriving from stems to roots influences the degree of root growth . If shoot tips are removed, the plant does not react just by outgrowth of lateral buds--which are supposed to replace to original lead . It also follows that smaller amount of auxin arriving to the roots results in slower growth of roots and the nutrients are subsequently in higher degree invested in the upper part of the plant, which hence starts to grow faster . </P>

Where is the auxin hormone made in a plant stem