Photosynthesis by carrot tissue cultures.

Area of Science:

• Plant Physiology
• Biochemistry

Background:

• Carrot callus cultures offer a model system for studying plant cell metabolism.
• Understanding CO2 fixation pathways is crucial for plant productivity.

Purpose of the Study:

• To quantify carbon dioxide fixation rates in carrot callus under varying light and CO2 conditions.
• To identify the main products of light-dependent and dark CO2 fixation.
• To investigate the influence of oxygen and chlorophyll on CO2 fixation.

Main Methods:

• Determination of (14)CO2 fixation rates in gaseous and liquid media.
• Measurement of net oxygen evolution using polarography.
• Assay of Ribulose-1,5-bisphosphate carboxylase and phosphoenolpyruvate carboxylase activities.
• Analysis of dry weight and chlorophyll content changes.

Main Results:

• Light-dependent CO2 fixation rates were approximately ten times higher than dark fixation, reaching 50-90 μmol/mg chlorophyll/h.
• Main products of light fixation included sucrose, alanine, glutamine, serine/glycine, and malic acid; dark fixation yielded glutamine and malic acid.
• Light fixation rates correlated linearly with chlorophyll levels, while dark fixation was independent of chlorophyll.
• Reduced oxygen partial pressure enhanced CO2 fixation rates.
• Carrot callus cultures showed dry weight increases even without external carbohydrates under optimal light and CO2.

Conclusions:

• Carrot callus cultures demonstrate significant photosynthetic CO2 fixation capabilities.
• Light intensity, CO2 concentration, and oxygen levels are critical factors influencing CO2 fixation efficiency.
• The study provides insights into the biochemical pathways and enzymatic activities involved in carbon assimilation in plant cell cultures.