Optical Projection Tomography (OPT)

The movies and images in the Inner World of Plants and their Guests, Inner world of Carnivorous Plants and Inner World of Cereals are not models or computer generated images, but real plants and insects captured in 3D using a microscopy technique called Optical Projection Tomography (OPT). This imaging technique helps us explore how elaborate leaves of carnivorous plants and cereals make themselves. Getting a three dimensional (3D) view is vital to capture development. For anything other than a growing linear file of cells or a flat sheet of expanding tissue, development involves deformations in 3-dimensions. We use OPT to capture 3D shape and gene activity at a variety of developmental stages and scales from specimens between 1mm and 2cm in size. OPT can be applied to a wide variety of plant material including leaves, flowers, seedlings, roots, seeds, embryos and meristems. At the highest resolution large individual cells can be seen in the context of the surrounding plant structure. 3D domains of gene expression can also be viewed. For naturally semi-transparent structures, such as Utricularia bladder traps, live 3D imaging using OPT allows growing plants to be studied. 3D gene expression patterns in living transgenic plants expressing fluorescent green florescent protein markers can also be visualised. In a recent paper we describe a new Macro Optical Projection Tomography scanner which enables imaging of plant and insect specimens up to 6cm in size.

OPT was invented by James Sharpe at the Medical Research Council laboratory in Edinburgh to study gene expression in developing mouse embryos. The method is similar to medical Computed Tomography, but uses light rather than X-rays. OPT works by projecting light through a specimen and capturing a series of shadow projections as the specimen is rotated. The images are processed using computer software which allows a 3-dimensional representation to be reconstructed. Once a scan has been reconstructed we use VolViewer software to look at sectional and volume views, make measurements, use landmarks to quantify growth in 3D, and collect images for animations shown in the Inner World of Plants and their Guests, Inner world of Carnivorous Plants and Inner World of Cereals.