Morphological Changes in Woody Stem of Prunus jamasakura under Simulated Microgravity

Abstract

When the four-week-old woody stem of Prunus jamasakura was grown under simulated microgravity condition on a three-dimensional clinostat, it bent at growth, and width of its secondary xylem decreased due to the reduction of fiber cell numbers and a smaller microfibril angle in the secondary cell wall, as reported in our previous paper. Gravity induces the development of the secondary xylem that supports the stem upward against the action of gravity. In this study, morphological changes of the tissues and cells were microscopically observed. Disorder was found in the concentric structure of tissues that organize the stem. The radial arrangement of the cells was also disturbed in the secondary xylem, and in the secondary phloem secondary cell walls of the bast fiber cells were undeveloped. These findings suggest that differentiation and development of the secondary xylem and the bast fiber cells are strongly controlled by terrestrial gravity. These tissue and cells functions to support the stem under the action of gravity. Furthermore, clinorotation induced disorder in the straight joint of vessel elements and the lattice-like structure of radial parenchyma cells, which is responsible for water transportation and storage, respectively. Gravity is an essential factor for keeping the division and differentiation normal in woody stem.

Changes in gravitational forces induce the modification of Arabidopsis thaliana silique pedicel positioning

“…In this study, the number of xylem vessel cells of the two lateral vascular bundles in the basal region of the pedicel was not significantly affected by the 3-D clinorotation, whereas the xylem vessel cells in the middle vascular bundles, especially in the adaxial vascular bundle of the 3-D clinorotated plants, appeared earlier than those of the 1  g control plants. This result is in agreement with the effect of the 3-D clinorotation on vessel development in woody stems of Prunus jamasakura (Yoneyama et al , 2004). Pedicel ontogeny in control plants revealed that the abaxial side vessel element was developmentally more advanced than the corresponding elements on the adaxial side of 3–5 DAF stage pedicels, and at this stage became sensitive to both 3-D and 2-D clinorotation.…”

Hypergravity Stimulus Enhances Primary Xylem Development and Decreases Mechanical Properties of Secondary Cell Walls in Inflorescence Stems of Arabidopsis thaliana

“…Gravitational force has been suggested to promote xylem formation in poplar (Populus tremula), when tension woods are formed (Andersson-Gunneras et al, 2003). Threedimensional clinorotation has been demonstrated to reduce both the number of fibre cells in secondary xylem and the angle of cellulose microfibrils in the secondary cell wall in Prunus spachiana (Nakamura et al, 1999), and to change the morphology of fibre cells and vessel elements as well (Yoneyama et al, 2004). These observations lead to the suggestion that changes in gravitational conditions affect morphology and mechanical properties of xylem vessels.…”

Effects of hypergravity conditions on elongation growth and lignin formation in the inflorescence stem of Arabidopsis thaliana

“…There are several reports indicating that the formation of lignin is suppressed under microgravity conditions in space (Cowles et al 1984;Nedukha 1996). Clinorotation suppresses the formation of the xylem (Nakamura et al 1999;Yoneyama et al 2004), a tissue with intensively lignified secondary cell walls. These facts suggest that hypergravity conditions should stimulate lignin formation in secondary cell walls.…”