Prochlorophyta is a sub-class of Chlorophyta that includes a group of photosynthetic algae. They mainly include picoplankton which are oligotrophic microscopic algae found in tropical waters with poor nutrient content. They were first discovered in the Great Barrier Reef in Mexico.
Characteristics of Prochlorophyta
Lewin erected the division in 1976 after the discovery of algae Prochloron in the oral cavity of Didemnid ascidians. The alga had prokaryotic properties coupled with the presence of chlorophyll b and thylakoids. He considered the alga as a missing link in the evolution of green alga from bacteria.
The discovery of Prochloron (P.didemnia 1986) and Prochlorococcus monicus were reported with similar characteristics. Now the division has three genera under Prochlorophyceae.
The characteristics of Prochlorophyta are the following.
- Prokaryotic nucleus
- Cellulose is absent in the cell wall. Muramic acid is acryl glucosamine that forms the cell wall (bacterial property)
- Thylakoids arranged in stacks (similar to Chlorophyta but differ from gametophyte)
- Photosynthetic pigments are divinyl-chlorophyll, chlorophyll a, b, beta-carotene, zeaxanthin, and cryptoxanthin
- They are widely seen in nutrient-poor waters and divinyl-chlorophyll helps them perform photosynthesis under these conditions.
- Lacks phycobiliproteins (differ from Cyanophyta)
- Growth of binary fission (bacterial property)
- Oxygenic photosynthesis
- Contains enzymes or chlorophyll a oxygenase (CAO) and the gene coding CAO and the gene sequence inhibit close similarities with that of Chlorophyceae CAO.
- Algae lead a symbiotic life with Didemnid ascidians (primochloris is a free-living marine form)
While Lewis claimed the algae to be the link between green algae and prokaryotes but Chadefaud opposed the proposal (because chlorophyll a and b have arisen several times during evolution).
Gibbs believed that prochloron-like ancestors might be given rise endosymbiotically to green algal chloroplasts (while that of red algae evolved from coccoid cyanobacteria).
Some believe that the characteristics of Prochlorophyta resembled that of Cyanophyceae and thus have evolved from Cyanobacteria by developing the ability to produce chlorophyll b.
Bacteriologists consider the algae as oxygenic photosynthesizing green algae and are included under the family Prochlorobacteriaceae.
