Plant Physiology

Plant Physiology (Biology 327) - Dr. Stephen G. Saupe; College of St. Benedict/ St. John's University; Biology Department; Collegeville, MN 56321; (320) 363 - 2782; (320) 363 - 3202, fax; ssaupe@csbsju.edu

Direct Measurement of the Stomatal Aperture by the Oil Immersion Technique

Stomatal aperture is sensitive to a variety of internal and external parameters. The plant requires this tight control of stomatal aperture in order to regulate the rates of photosynthesis/ transpiration; that is, the entry and exit of water and gases from a leaf. Since the stomata are so sensitive, they provide good indication of a plant's physiological state. To measure the aperture:

Protocol:

Place a drop of immersion oil on a microscope slide.
Prepare an epidermal strip and immediately place it cuticle side up in the drop of oil.
With the forceps, carefully distribute some of the oil on top of the strip.
Gently smooth out the strip if necessary and over with a cover glass.
Examine the slide with the high power objective (430X) and measure the aperture with a calibrated ocular micrometer. Measure the stomata at the widest point from the inside wall of one guard cell to the inside wall of the other.
Measure 10 stomata in 5 fields per strip. Repeat with 4 other strips.
Record your data in a table and then calculate the mean aperture.

Notes:

The oil serves to fix the stoma. Alternate techniques are available for fixing (i.e. immersion in alcohol; preparation of silicon rubber replicas)
Apertures should be measured within an hour of strip preparation.
Do not measure stomata in areas that were crushed by the forceps during stripping.