M2.2.1- Imaging Technologies

Question 1

MRI: Magnetic resonance imaging

Answer 1

Uses radio waves and magnetic field to generate a 3D image. Structure can be analysed in greater detail

Pro:
* 3D image allows greater detail for analysis
* Non-disruptive in-vivo analysis
* Allows imaging of water by adding spatial information

Con:
* Expensive
* Not portable → cannot be conducted on plants in-situ → physiological functioning of the plant may be altered from its natural state when it is removed from its environment

Question 2

PET: Positron Emission Tomography

Answer 2

Detects information about transportation and processes by detecting radioisotopes.
* A PET camera scans a patient and detects the radioisotopes which has accumulated in a target organ. The detected radioactivity is shown as an image on a computer
* Useful for detecting cancers in lymph nodes + bronchi + malignant melanomas
* Most commonly used active molecule is FDG, which is a marker for the tissue uptake of glucose.

Pro:
* Non-disruptive in-vivo analysis
* Highly sensitive
* Medical use + allow scientists to measure the changes of metabolic and transport mechanisms in plants

Con:
* Low spatial resolution in PET images → difficulties localising areas of activity in organs

Question 3

Micro-CT: X-Ray Computed Microtomography

Answer 3

• Like CT scans, X-rays rotate around the specimen.
• Thousands of images from different angles are compiled to reconstruct a 3D image in which any angle can be studied.
• The spatial arrangement of internal tissues of plants can be studied.

Pro:

• Non-destructive in-vivo analysis
• The spatial arrangement of internal tissues of plants can be studied because any angle can be studied

Con:
* High doses of X-ray can harm living tissue and break DNA
* Long scan times

Question 4

RRIS: Real Time Radioactive Imaging System

Answer 4

Using radioisotope emissions, the movement of substances are studied in real time.
Captures images of plant producing food, transporting food
* Uses radioistopes including Cesium-137, 137-Cs

Pro:
* Non-disruptive in-vivo analysis
* Real-time component allows ion transport to be analysed, as ions are continuously moving in plants
* Sequential images → coherence of transport process

Con:
* Light converted from radiation is very weak, so dark conditions is required to take images
* Camera in RRIS has a high sensitivity → detector can be damaged if exposed to strong light

Question 5

How has the use of radioisotopes enhanced modern understandings of plant processes?

Answer 5

Initially, it was thought that sunlight acted upon carbon dioxide in photosynthesis.

After Melvin Calvin used radioactive tracer carbon-14:

• Sunlight acts on chlorophyll, not carbon dioxide.
• CO2 is manufactured into organic compounds later.
• Water with radioactive O2 was supplied to plants, and radioactive O2 was released.
• This means that O2 is supplied from water, not carbon dioxide, and that water is important for photosynthesis.
• PET scanner tracks the movement of glucose through the plant using FDG