Stomata

• Stomata facilitate carbon capture and photosynthesis
• Low stomatal density in early plants. This is due to the high CO2 concentration in the atmosphere.
• More co2 = less stomata
• Guard cell walls have thickenings called casparian strips which prevent water from entering the cell via plasmodesmata.
• High stomatal density in modern plants. Due to low atmospheric CO2 levels, more stomata are needed to absorb enough CO2 for photosynthesis.
• non vascular plants have a pore which is permanently open
• hornworts have stomata on the underside of the leaf and are found in freshwater lakes and ponds
• Abscisic acid (ABA) is the primary hormone that regulates stress. Upregulation in stomata for reduction of turgor
• Increasing of ABA = stomata closing
• In hornworts ABA does not appear to have an effect.
• The aba experiments show there is not functional consistency within stomata across groups
• Conservation of function unlikely due to location change (sporophyte to gametophyte)
• megaphylls = leaves
• 85mya between land plants and plants with leaves
• The telome theory= evolutionary framework for leaf evolution.
• the telome hypothesis suggests that leaves evolved from modified shoot apices
• Planation= more lateral branches with lateral branches of the same size as the main branches
• Telome theory relies on the fossil record
• Rare devonian plant fossils with large leaves ( 390mya )
• Leaf energy balance = the energy supplied to the leaf by the light energy received by the leaf - the energy lost by the leaf. Facilitated by the stomata
• Low leaf areas due to temperature and light intensity affects photosynthesis and growth
• Diversification of leaf size and shape in late Devonian
• Positive feedback between roots and leaves/canopy cover