THE ROLE OF ABSCISIC ACID AND CALCIUM IN DETERMINING THE BEHAVIOUR OF ADAXIAL AND ABAXIAL STOMATA

Area of Science:

• Plant Physiology
• Plant Biology
• Plant Hormones

Background:

• Stomatal opening differences between adaxial and abaxial leaf epidermis are observed.
• Previous research suggested endogenous auxin levels as a potential cause.

Purpose of the Study:

• To investigate the reasons behind differential stomatal opening on adaxial and abaxial leaf surfaces.
• To explore the role of calcium ions and abscisic acid (ABA) sensitivity in stomatal responses.

Main Methods:

• Comparative analysis of stomatal sensitivity to externally supplied abscisic acid (ABA).
• Treatment with lanthanum ions to block calcium channels.
• Use of the chelating agent EGTA to assess calcium ion involvement.
• Experiments with EGTA and fusicoccin to determine additive or independent effects.

Main Results:

• Adaxial stomata exhibited higher sensitivity to ABA compared to abaxial stomata.
• Lanthanum ions significantly increased adaxial stomatal aperture but had minimal effect on abaxial stomata.
• EGTA treatment abolished the differential behavior between adaxial and abaxial stomata, indicating a dominant role for calcium ions.
• EGTA and fusicoccin showed independent and additive effects, suggesting distinct mechanisms of action.

Conclusions:

• Differential endogenous calcium ion concentrations in leaf epidermes likely contribute to varying ABA sensitivity.
• Isolated epidermis serves as a viable model for studying hormone response mechanisms.
• Calcium ions play a crucial, dominant role in regulating differential stomatal responses to ABA.