Responses of stomata to changes in humidity

Area of Science:

• Plant Physiology
• Plant Anatomy
• Environmental Plant Science

Background:

• Polypodium vulgare and Valerianella locusta leaves possess a subepidermal airspace between the lower epidermis and mesophyll.
• This anatomical feature creates unique humidity conditions influencing epidermal cell behavior.

Purpose of the Study:

• To investigate stomatal reactions to varying humidity levels in a simulated subepidermal airspace environment.
• To understand the role of guard cells as humidity sensors in regulating plant transpiration.

Main Methods:

• Preparation of epidermal stripes from Polypodium vulgare leaves to mimic natural subepidermal airspaces.
• Exposure of the inner epidermal surface to high humidity and the outer surface to controlled varying humidity levels.
• Microscopic observation and photographic determination of stomatal aperture changes in response to humidity treatments.

Main Results:

• Stomata rapidly closed in response to dry air and opened in moist air on the outer epidermal surface.
• Stomatal opening and closing movements were reversible and repeatable up to 15 times with the same stoma.
• Stomatal aperture was dependent on both ambient air water potential and subepidermal airspace humidity.

Conclusions:

• Guard cells function as sensitive humidity sensors, measuring water potential differences across the epidermis.
• Peristomatal transpiration likely drives stomatal responses, allowing aperture control based on individual transpiration conditions.
• This mechanism is vital for plant water conservation, enabling reduced transpiration during decreasing ambient humidity.