Auxins

AUXINS STIMULATE GROWTH OF MAIN, APICAL SHOOT

auxin molecules bind to recptors in cell surface membrane, pH5 optimum for enzymes that keep cell fall flexible- strech more easily.

mature, auxin decreases, pH decreases, rigid walls, cell no longer expands and grows

HIGH CONCENTRATIONS OF AUZIN SUPRESS GROWTH OF LATERAL SHOOTS

high levels, cause apical dominance, lateral shoots inhibited as hormones move down stem, further down stem hormone lower more shoots grow

EXPERIMENT: apical shoot removed, auxin producing cells removed, no auxin, lateral shoots freed so grow faster. If auxin applied, lateral shoots growth supressed

LOW CONCENTRATION OF AUXINS PROMOTES ROOT GROWTH, UP TO A GIVEN CONC

auxin produced in root tips and auxin also reaches roots in low concentrations

EXPERIMENT: apical shoot removed, suxin reaching roots greatly reduced, root growth slows. replaced artificially at cut, restores growth. High auxin conc inhibits.