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MICRO-STRUCTURE ANALYSIS OF PLANT TISSUES - Lublin

MICRO-STRUCTURE ANALYSIS OF PLANT TISSUES - Lublin

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The thickness of the focal layer is also related to the lens used (its numeric<br />

aperture, NA). For example, M. Petran (1995) reports, for the Tandem Scanning<br />

Reflected Light Microscope (TSRLM), that for an immersion lens of 40X 0.74<br />

NA the image changes totally with every 5 µm focusing step in the Z axis, while<br />

for a 40X 1.3 NA lens – with every 1µm. Nevertheless, the difference in<br />

comparison to the image generated by the conventional optical microscope is<br />

notable. James B. Powley (1989) enumerates, among others the following<br />

advantages of the confocal microscope:<br />

1. Reduction in the loss of image resolution resulting from light diffusion<br />

(improved contrast).<br />

2. Increase in effective resolution.<br />

3. Improvement in the signal-to-noise ratio.<br />

4. Possibility of studying thick objects and light diffusing objects.<br />

5. Possibility of theoretically unlimited extent scanning in the X-Y plane.<br />

6. Scanning in the Z axis.<br />

7. Possibility of electronic change of magnification rate.<br />

8. Possibility of quantitative evaluation of the optical properties of the<br />

sample tested.<br />

An example of the micro-structure of potato tuber tissue, obtained with the<br />

TSRLM confocal microscope (described below) is shown in Fig. 2.22. Comparing<br />

the image with that in Fig. 2.18, one can observe a distinct improvement in the<br />

contrast; the cell walls are visible as bright lines, while the interior of the cells<br />

is almost black. The image originates from a very thin layer of the tissue, hence<br />

such an optical section may also include cell membranes oriented in parallel<br />

or almost-parallel to the scan plane, visible as bright areas in the image. Such an<br />

image, due to its high contrast, is suitable for e.g. analysis of the geometric<br />

features of the mechanical skeleton of plant tissue.<br />

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