Halogenation of IAA by touch stimulus for rapid and differential growths of the Madeira vine

Abstract

Abstract Background The thigmotropic response triggers two actions of faster growth and differential growth. Madeira vine (MV) grows 30 times faster after encountering a support. The question as to “how the vine can provide sufficient amounts of active auxin and effectively transport it into the cells for fast growth in such a short time” has not yet been answered.Results In vivo x-ray diffraction made on live MV stems revel the appearance of crystallized IAA (C10H9NO2), 4-Cl-IAA (C10H8ClNO2) and 6-Cl-IAA (C10H8ClNO2) in the stems. Small angle neutron scattering spectra of the IAA extracted from MVs stem reveal a progressive increase in the size of crystallized IAA transported downward from the apex of the shoots. High resolution X-ray diffractions made on the extracted IAA reveal significantly larger amounts of 4-Cl-IAA and 6-Cl-IAA in the climbing MVs than in the swaying around MVs. The gas chromatography-mass spectrometry spectra reveal the production of 9% more IAA and 90% more 4-Cl-IAA + 6-Cl-IAA at the apexes of climbing MVs than swaying MVs. More 4-Cl-IAA + 6-Cl-IAA were transported to the contact-free side than to the contact side of the vine. In vivo neutron tomography of naturally climbing MVs reveals a substantially higher H+ concentration in the contact-free parts than in the contact parts.Conclusions Enhanced expressions of auxin 4-Cl-IAA (C10H8ClNO2) and 6-Cl-IAA (C10H8ClNO2) through halogenation of IAA (C10H9NO2) triggered by the physical touch, rather than accumulation of auxin IAA, are the main sources to drive faster growth of Madeira vine. The IAA, 4-Cl-IAA and 6-Cl-IAA molecules produced in apex link into crystallized form, rather than stay in the molecular form, upon transporting downward to the stem.