Biology subjects

Kamachi, H.

Publications and source records attributed to Kamachi, H..

2 recordsLinked to original sources

bioRxiv2023

Prolonged exposure to hypergravity increases number and size of cells and enhances lignin deposition in the stem of Arabidopsis thaliana (L.) Heynh.

We have performed a lab-based hypergravity cultivation experiment using a centrifuge equipped with a lighting system and examined long-term effects of hypergravity on the development of the main axis (stem) of the Arabidopsis (Arabidopsis thaliana (L.) Heynh.) primary inflorescence. Plants grown under 1 x g (gravitational acceleration on Earth) conditions for 20-23 days and having the first visible flower bud were exposed to hypergravity at 8 x g for 10 days. We analyzed the effect of prolonged hypergravity conditions on growth, lignin deposition, and tissue anatomy of the main axis. As a result, the length of the main axis decreased and cross-sectional area, dry mass per unit length, cell number, lignin content of the main axis significantly increased under hypergravity. Lignin content in the rosette leaves also increased when they were exposed to hypergravity during their development. Except for interfascicular fibers, cross-sectional areas of the tissues composing the internode significantly increased under hypergravity in most type of the tissues in the basal part than the apical part of the main axis, indicating that the effect of hypergravity is more pronounced in the basal part than the apical part. The number of cells in fascicular cambium and xylem significantly increased under hypergravity both in the apical and basal internodes of the main axis, indicating a possibility that hypergravity stimulates procambium activity to produce xylem element more than phloem element. The main axis was suggested to be strengthened through changes in its morphological characteristics as well as lignin deposition under prolonged hypergravity conditions.

plant biology↗

bioRxiv2022

Three-dimensional visualization of moss rhizoid system by refraction-contrast X-ray micro-computed tomography

Land plants have two types of shoot-supporting systems, root system and rhizoid system, in vascular plants and bryophytes. However, since the evolutionary origin of the systems are different, how much they exploit common systems or distinct systems to architect their structures are largely unknown. To understand the regulatory mechanism how bryophytes architect rhizoid system responding to an environmental factor, such as gravity, and compare it with the root system of vascular plants, we have developed the methodology to visualize and quantitatively analyze the rhizoid system of the moss, Physcomitrium patens in 3D. The rhizoids having the diameter of 21.3 m on the average were visualized by refraction-contrast X-ray micro-CT using coherent X-ray optics available at synchrotron radiation facility SPring-8. Three types of shape (ring-shape, line, black circle) observed in tomographic slices of specimens embedded in paraffin were confirmed to be the rhizoids by optical and electron microscopy. Comprehensive automatic segmentation of the rhizoids which appeared in different three form types in tomograms was tested by a method using Canny edge detector or machine learning. Accuracy of output images was evaluated by comparing with the manually-segmented ground truth images using measures such as F1 score and IoU, revealing that the automatic segmentation using the machine learning was more effective than that using Canny edge detector. Thus, machine learning-based skeletonized 3D model revealed quite dense distribution of rhizoids, which was similar to root system architecture in vascular plants. We successfully visualized the moss rhizoid system in 3D for the first time.

plant biology↗