Variation in photosynthetic efficiency among maize cultivars and its implications for breeding strategy

Area of Science:

• Plant Physiology
• Crop Science
• Molecular Biology

Background:

• Maize is a globally vital crop, yet factors influencing its photosynthetic efficiency and genetic variability remain underexplored.
• Limited knowledge exists on variations in steady-state and dynamic photosynthetic efficiency across different maize cultivars.

Purpose of the Study:

• Investigate anatomical and physiological mechanisms behind photosynthetic CO2 assimilation variability in maize cultivars.
• Compare steady-state and dynamic photosynthetic efficiency under fluctuating light conditions.

Main Methods:

• Assessed photosynthetic CO2 assimilation rates (Asat) under steady-state conditions.
• Measured cumulative CO2 fixation and loss of potential CO2 uptake (Closs) during light induction.
• Analyzed leaf anatomy (mesophyll to bundle sheath cell area ratio) and stomatal conductance (gs) kinetics.
• Correlated gs kinetics with the expression of ethylene synthesis genes (acs1, gad1) and stomatal density.

Main Results:

• Steady-state Asat varied significantly (50.2–63.1µmol CO2 m-2 s-1), linked to leaf anatomical ratios.
• Dynamic efficiency showed greater variation; Closs ranged from 23% to 47%.
• Closs variation was primarily driven by gs kinetics, correlating with acs1 and gad1 gene expression, not stomatal density.

Conclusions:

• Dynamic photosynthetic efficiency exhibits greater variability than steady-state efficiency in maize cultivars.
• Stomatal conductance (gs) kinetics and associated ethylene synthesis gene expression are key targets for improving maize photosynthetic efficiency and yield.