https://emsenn.net/tags/growthregulation/ Recent content in GrowthRegulation on emsenn.net Hugo en-us Thu, 02 Apr 2026 00:00:00 +0000 https://emsenn.net/library/domains/science/domains/biology/domains/botany/terms/auxin/ Thu, 02 Apr 2026 00:00:00 +0000 https://emsenn.net/library/domains/science/domains/biology/domains/botany/terms/auxin/ <p>Auxin: the primary plant growth hormone, regulating cell elongation, apical dominance, phototropism, gravitropism, root initiation, fruit development, and vascular differentiation. The main natural auxin is indole-3-acetic acid (IAA), first isolated by the botanist Went in 1926 following Darwin&rsquo;s classical observations of phototropic bending in grass seedlings.</p> <h2 id="biosynthesis-and-transport">Biosynthesis and transport</h2> <p>Auxin is synthesized primarily in the shoot apex through the TAA/YUC (tryptophan aminotransferase / YUCCA) pathway: tryptophan → indole-3-pyruvic acid (IPA) → IAA. The enzyme TAA1 catalyzes the first step; the YUCCA family of flavin monooxygenases catalyzes the second. Once produced, IAA moves through tissues via polar transport — a directional basipetal (downward) movement mediated by PIN-FORMED (PIN) efflux carriers and AUX1/LAX influx carriers on the plasma membrane. This polar transport is unique among plant hormones: auxin cannot move acropetally (upward) against the PIN gradient. The directionality of PIN localization determines the direction of auxin flow and thus the spatial pattern of growth.</p>