Low bundle sheath carbonic anhydrase is apparently essential for effective c(4) pathway operation
1CSIRO, Division of Plant Industry, GPO Box 1600, Canberra City A.C.T. 2601, Australia.
Plant Physiology
|April 1, 1988
Summary
Bundle sheath cells in C(4) plants have very low carbonic anhydrase activity, crucial for efficient photosynthesis. This low level helps maintain high carbon dioxide concentrations, suppressing photorespiration.
Area of Science:
- Plant Physiology
- Biochemistry
- Photosynthesis Research
Background:
- Carbonic anhydrase (CA) plays a role in CO2 concentration mechanisms in plants.
- C(4) photosynthesis relies on efficient CO2 delivery to the bundle sheath cells.
- The precise role and localization of CA in C(4) photosynthesis remain areas of investigation.
Purpose of the Study:
- To quantify carbonic anhydrase activity in C(4) bundle sheath cells.
- To determine if CA levels in bundle sheath cells are compatible with efficient C(4) pathway function.
- To assess the importance of CA deficiency in bundle sheath cells for C(4) photosynthesis.
Main Methods:
- Enzyme assays were performed on extracts from C(4) plant leaves.
- Bundle sheath cell extracts were analyzed for carbonic anhydrase activity.
- Mesophyll cell contamination was assessed using marker enzymes like phosphoenolpyruvate carboxylase and pyruvate, Pi dikinase.
- Measured CA activity was compared to a calculated upper limit for efficient C(4) function.
Main Results:
- Bundle sheath cells exhibited minimal to no carbonic anhydrase activity.
- Estimated CA activity in bundle sheath cells was less than 1% of total leaf activity, even accounting for mesophyll contamination.
- The observed CA activity was significantly lower than the calculated upper limit required for efficient C(4) photosynthesis and photorespiration suppression.
Conclusions:
- A deficiency of carbonic anhydrase in bundle sheath cells is essential for the effective operation of the C(4) photosynthetic pathway.
- Low CA levels in bundle sheath cells facilitate high CO2 concentrations, thereby suppressing photorespiration.
- These findings support the hypothesis that specific enzyme localization and activity are critical for optimizing C(4) photosynthesis.
More Related Videos
08:04A New Approach for the Comparative Analysis of Multiprotein Complexes Based on 15N Metabolic Labeling and Quantitative Mass Spectrometry
Published on: March 13, 2014
10:46Evaluation of Photosynthetic Efficiency in Photorespiratory Mutants by Chlorophyll Fluorescence Analysis
Published on: December 9, 2022
Related Concept Videos
01:27C4 Pathway and CAM
Most plants use the C3 pathway for carbon fixation. However, some plants, such as sugar cane, corn, and cacti that grow in hot conditions, use alternative pathways to fix carbon and conserve energy loss due to photorespiration. Photorespiration is the process that occurs when the oxygen concentration is high. Under such conditions, the rubisco enzyme in the Calvin cycle binds O2 instead of CO2, which halts photosynthesis and consumes energy.
C4 Pathway
The C4 pathway is used by plants such as...
C4 Pathway
The C4 pathway is used by plants such as...
01:46The Calvin Benson Cycle
Ribulose 1,5- bisphosphate carboxylase/oxygenase (RuBisCo) is a critical enzyme that catalyzes carbon dioxide assimilation during photosynthesis. However, it is an inefficient enzyme, having an extremely slow catalytic rate. A typical enzyme can process about a thousand molecules per second; however, RuBisCo fixes only around three-carbon dioxides per second. Photosynthetic cells compensate for this slow rate by synthesizing very high amounts of RuBisCo, making it the most abundant single...
01:28Carbon-dioxide Fixation
Carbon dioxide fixation in prokaryotes enables the assimilation of inorganic carbon into organic molecules, supporting biosynthetic pathways, sustaining ecosystems, and contributing to the global carbon cycle. It also has industrial applications in carbon capture and bioproduct synthesis. Autotrophic organisms rely on this process to utilize CO₂ as a carbon source in diverse environments.The Calvin CycleThe Calvin cycle is the most widespread carbon fixation mechanism, primarily used by...
01:40The Calvin Cycle
OverviewOxygenic photosynthesis plays a central role in the global carbon and oxygen cycles. The carbohydrates produced support nearly all food webs, while the oxygen by‑product enables aerobic life.Light‑dependent and light‑independent reactionsPhotosynthesis occurs in two main stages, each in a different part of the chloroplast: light‑dependent reactions and light‑independent reactions, also called the Calvin‑Benson cycle or simply the Calvin cycle.Light‑dependent reactions take place in the...
01:57Adaptations that Reduce Water Loss
Though evaporation from plant leaves drives transpiration, it also results in loss of water. Because water is critical for photosynthetic reactions and other cellular processes, evolutionary pressures on plants in different environments have driven the acquisition of adaptations that reduce water loss.
01:19Allosteric Proteins-ATCase
Binding sites linkages can regulate a protein's function. For example, enzyme activity is often regulated through a feedback mechanism where the end product of the biochemical process serves as an inhibitor.
Aspartate transcarbamoylase (ATCase) is a cytosolic enzyme that catalyzes the condensation of L-aspartate and carbamoyl phosphate to N-carbamoyl-L-aspartate. This reaction is the first step in pyrimidine biosynthesis. UTP and CTP, the end products of the pyrimidine synthesis pathway,...
Aspartate transcarbamoylase (ATCase) is a cytosolic enzyme that catalyzes the condensation of L-aspartate and carbamoyl phosphate to N-carbamoyl-L-aspartate. This reaction is the first step in pyrimidine biosynthesis. UTP and CTP, the end products of the pyrimidine synthesis pathway,...