Related Experiment Video
Updated: Aug 8, 2026
10:18
Analysis of Protein Import into Chloroplasts Isolated from Stressed Plants
Published on: November 1, 2016
Ochromonas mitochondria contain a specific chloroplast protein
1Department of Biology, McGill University, Montreal, Quebec H3A 1B1, Canada.
Summary
Antibodies targeting the small subunit of ribulose-1,5-bisphosphate carboxylase were found in both mitochondria and chloroplasts of Ochromonas danica. This suggests the small subunit gene may have migrated to mitochondria.
Area of Science:
- Plant Biology
- Cell Biology
- Biochemistry
Background:
- Ribulose-1,5-bisphosphate carboxylase (RuBisCO) is a key enzyme in photosynthesis.
- The enzyme's subunits can be encoded by nuclear, chloroplast, or mitochondrial genomes.
- Previous research indicated homologous DNA sequences in mitochondrial and chloroplast genomes of higher plants.
Purpose of the Study:
- To investigate the localization of RuBisCO subunits in Ochromonas danica and Chlamydomonas reinhardtii.
- To explore the potential origin and expression of the RuBisCO small subunit in mitochondria.
Main Methods:
- Immunoelectron microscopy using protein A-gold technique.
- Antibody labeling against small and large subunits of RuBisCO.
- Quantitative analysis of antibody staining in O. danica cells under different light conditions.
Main Results:
- Antibody against the small subunit labeled both mitochondria and chloroplasts in O. danica.
- The same antibody labeled only chloroplasts in C. reinhardtii.
- Mitochondrial staining for the small subunit increased with light exposure in O. danica.
- Antibody against the large subunit did not label mitochondria in either species.
Conclusions:
- The small subunit of RuBisCO is present in both chloroplasts and mitochondria of O. danica.
- Mitochondrial expression of the small subunit appears to be light-regulated.
- The findings support the hypothesis of gene migration for the RuBisCO small subunit from the nucleus or chloroplast to the mitochondria.
Related Concept Videos
01:07Anatomy of Chloroplasts
Green algae and plants, including green stems and unripe fruit, harbor chloroplasts—the vital organelles where photosynthesis takes place. In plants, the highest density of chloroplasts is found in the mesophyll cells of leaves.
01:08The Anatomy of Chloroplasts
Green algae and plants, including green stems and unripe fruit, harbor specialized organelles called chloroplasts to carry out photosynthesis. They coordinate both stages of photosynthesis — the light-dependent reactions and the light-independent reactions. The light-dependent reactions use sunlight to release oxygen and produce chemical energy in the form of ATP and NADPH, and the light-independent reactions capture CO2 and use ATP and NADPH to produce sugar.
Structure of Chloroplasts
A...
Structure of Chloroplasts
A...
01:39Mitochondrial Protein Sorting
Mitochondria are double-membrane organelles of the eukaryotes involved in cellular metabolism, signaling, ATP synthesis, and programmed cell death. Each of these processes requires specific proteins and enzymes that must be correctly sorted to the right mitochondrial subcompartment for the proper functioning of the organelle.
Most of these mitochondrial proteins are encoded by the nucleus and imported to the mitochondria as unfolded or loosely folded precursors. Mitochondrial precursors...
Most of these mitochondrial proteins are encoded by the nucleus and imported to the mitochondria as unfolded or loosely folded precursors. Mitochondrial precursors...
01:24Protein Transport to the Stroma
Chloroplasts are triple membrane structures with an outer membrane, an inner membrane, and a thylakoid membrane, each containing distinct metabolite transporters, membrane translocons, and enzymes. Appropriate sorting and translocating these proteins to their correct membrane systems is essential for chloroplast function.
Protein complexes called the translocon of the outer chloroplast membrane or TOC complex, and the translocon of the inner chloroplast membrane or TIC complex mediate the...
Protein complexes called the translocon of the outer chloroplast membrane or TOC complex, and the translocon of the inner chloroplast membrane or TIC complex mediate the...
01:11Protein Transport to the Outer Chloroplast Membrane
Chloroplast outer membrane proteins encoded by the nucleus are synthesized in the cytosol. Soon after synthesis, they bind cytosolic factors such as 14-3-3 protein and the Hsp70 chaperones that keep these precursors in an unfolded state until their translocation.
Two models describe the mechanism of precursor recognition and entry across the outer membrane through the TOC complex. Model 1 suggests the newly synthesized precursor binds to the TOC receptor 159 and forms a complex.
Two models describe the mechanism of precursor recognition and entry across the outer membrane through the TOC complex. Model 1 suggests the newly synthesized precursor binds to the TOC receptor 159 and forms a complex.
01:18Protein Transport to the Inner Chloroplast Membrane
Proteins targeted to the inner chloroplast membrane, or plastid proteins, are transported by two general pathways: the stop-transfer and the re-insertion or post-import pathways. Most plastid proteins carry N-terminal transit sequences and internal import sequences targeting it to the specific chloroplast subcompartment. Proteins targeted by the stop-transfer pathway have internal hydrophobic sequences that inhibit their translocation into the stroma. As a result, these precursors are arrested...