抄録
Indole-3-acetic acid (IAA), a major native auxin, has been shown to be involved in many physiological events. Monocot coleoptiles have been used for investigation of IAA production and IAA transport. In previous our work, it has been suggested that IAA is produced in the coleoptile tips from tryptophan and the synthesized IAA moves toward basal parts in a polar manner by ZmPIN proteins. In gravitropic response, it has been postulated that re-distribution of IAA induces gravitropic bending. However, whether that the re-distribution of IAA or IAA molecules itself is necessity factor for gravitorpic bending or not is unclear. When NPA and BFA are treated into inside of the top 2mm of the coleoptile, the amount of free IAA diffused to agar receiver from the 3-mm section started immediately to decrease. NPA treatment did not affect the cellular ZmPIN localization, but BFA treatment caused the accumulation of ZmPIN in cellular vesicles which achieve perinuclear position. In addition, gravity bending was completely suppressed by the local tip treatment of the transport inhibitors. In fact, NPA caused the accumulation of IAA at the top region and at the lower parts there are quit low amounts of IAA, as well as no differential distribution of IAA between upper and lower half. The present results indicated that correct distribution of IAA in the coleoptiles after gravistimulus is absolutely necessary for gravitropic bending; the IAA is transported from IAA synthetic coleoptile tip.
