Walking under zero-gravity conditions.

In higher plants, some organs such as roots, hypocotyls, and stems, can sense the direction of gravity to regulate their orientation. Gravitropic response is composed of four steps; 1. gravity sensing and conversion of physical stimuli to biochemical signals, 2. intracellular signal transduction in gravity sensing cells, 3. signal transmitting to responding tissues, 4. differential growth of organs. Here we focus on the former two steps. Recent studies using modern technique have gradually unveiled early events and mechanism of gravitropic response. Genetic approach provided evidences that strongly support the classical theory for gravity sensing (step 1). Computational analysis suggested the existence of another gravity sensing mechanism in roots. Spatial and temporal ion imaging in living organs in real time provided information on step 2. In addition, reverse genetic approach suggested asymmetrical intracellular distribution of auxin transporter [correction of transpoter] is a possible link between step 2 and 3. However, molecular basis of the signaling mechanism remains unknown. We believe extensive molecular genetic approach combined with recent techniques cited here shed the light to this ambiguous area of research.

Gravitation↗

PubMed2003

[Control of morphogenesis of woody plant by gravity on earth].

Using the weeping branch of Japanese flowering cherry tree and its woody stem of the seedling grown under simulated microgravity condition by three dimensional clinostat, it was elucidated that the morphogenesis of its secondary xylem supporting the plant itself to grow upward is seriously controlled by gravity on earth with a sedimentable amyloplast as its sensor. Space experiment of woody plant is expected to elucidate such problem.

Gravitation↗