Stomatal and pavement cell density linked to leaf internal CO2 concentration.

Area of Science:

• Plant physiology
• Plant development
• Environmental stress response

Background:

• Stomatal density (SD) typically decreases with rising atmospheric CO2 (Ca), but other factors like light, humidity, and drought also influence it through systemic signaling.
• The precise mechanism by which CO2 concentration influences SD remains incompletely understood, particularly the role of internal leaf CO2 (Ci) versus external Ca.

Purpose of the Study:

• To test if internal CO2 concentration (Ci) or atmospheric CO2 (Ca) is the primary driver of stomatal density (SD).
• To investigate whether cotyledons, as early photosynthetic organs, are influenced by systemic signals in regulating SD.

Main Methods:

• Four plant species (sunflower, beech, arabidopsis, garden cress) were grown under varied conditions to manipulate Ci while keeping Ca constant.
• Stomatal density (SD), pavement cell density (PCD), and stomatal index (SI) were measured in cotyledons and first leaves.
• (13)C abundance was used to estimate the effective Ci during leaf development.

Main Results:

• A negative correlation between stomatal density (SD) and internal CO2 concentration (Ci) was observed in the leaves of all four species across different treatments.
• Pavement cell density (PCD) responded similarly to Ci, resulting in largely unaffected stomatal index (SI).
• Cotyledon SD and PCD were insensitive to Ci, suggesting a lack of systemic signaling in these early organs.

Conclusions:

• Internal CO2 concentration (Ci) or a related factor is proposed to be crucial in modulating SD and PCD during epidermis development and leaf expansion.
• The absence of a Ci-SD relationship in cotyledons underscores their importance in perceiving CO2 signals and long-distance transport.