The emergence of molecular oxygen changed the Earth and the life on it irreversibly and is responsible for the current global environment and ecosystem. Oxygen was produced as a byproduct of the oxygenic photosynthesis that appeared in cyanobacteria (blue-green algae), which may date back 3.5 billion years. Since then, oxygen has been oxidizing the atmosphere and oceans. There were two great oxygenation events, GOE-I and GOE-II, that occurred around 2.5 and 8 billion years ago. After the first“ snowball Earth” event, GOE-I triggered the evolution of eukaryotes. Oxygenic photosynthesis was transferred to eukaryotes and generated eukaryotic algae possessing plastids, called primary plants, via primary endosymbiosis. Plastids spread to various eukaryotic lineages via the endosymbiosis of red and green algae (secondary endosymbiosis). These new algal lineages are known as secondary plants. GOE-II drove the evolution of multicellular organisms. Green algae evolved into land plants and contributed to the development of the terrestrial ecosystem. The secondary plants dominated the ocean at the boundary between the Paleozoic and Mesozoic eras. They helped to form today's marine ecosystem and continue to play important roles in driving the carbon cycle and circulation of water and sulfur. However, the diversity of algae is not well understood even today. Research is needed to understand the true contribution made by algae to the global ecosystem.

To obtain the relation between cellular polyamine distribution profiles and multicellular evolution in green algae, we acid-extracted polyamines from 59 additional unicellular, colonial and multicellular green-algal samples (52 species), newly analyzed them with HPLC and HPGC, and compared them with 124 previously analyzed green algal polyamine profiles. Tetra-amines, norspermine and/or spermine, which are distributed as major polyamines predominantly in multicellular, macro green algae, were found also in unicellular photobiontic Trebouxia species and endosymbiotic Chlorella variabilis (Trebouxiophyceae), respectively. In the class Chlorophyceae, colonial freshwater Volvox, Pleodorina, Eudorina, Yamagishiella, Pandorina, Tetrabaena and Gonium (Volvocales) always contain putrescine, norspermidine and spermidine as major polyamines, similar to unicellular Chlamydomonas and Haematococcus, indicating that there is no correlation between their colony-forming and polyamine profiles. A novel triamine, aminobutylcadaverine, homospermidine and homospermine were all detected as minor polyamines in another colonial alga, Westella (Sphaeropleales). Furthermore, the aminobutylcadaverine level increased, and novel tetra-amines N¹-aminopentylspermidine and N ⁸-aminopentylspermidine appeared in a culture supplemented with 1 mM cadaverine. The occurrence of thermospermine was limited in multicellular thallic freshwater Prasiola (Trebouxiophyceae) and multicellular thallic marine Ulva (Ulvophyceae). Caldopentamine, homocaldopentamine and/or thermopentamine were distributed as minor polyamines in unicellular coenocytic Codium, multicellular branched-filamentous Aegagropila, thallic Monostroma (Ulvophyceae) and filamentous Spirogyra (Zygnematophyceae) in addition to Prasiola and Ulva, suggesting that the occurrence of penta-amines is related to multicellular and macro green-algal evolution.

To consider the phylogenetic significance of cellular polyamine distribution profiles in multicellular red-algal evolution, polyamines procured through acid extraction from 27 additional red algae species (29 strains) including 18 species (19 strains) of marine multicellular species (seaweeds) were newly analyzed by HPLC and HPGC-MS, and compared with 21 previously analyzed red-algal polyamine profiles. In the unicellular thermoacidophilic order Cyanidiales, Cyanidium and Cyanidioschyzon contained putrescine, spermidine and spermine, and Galdieria contained norspermidine and norspermine in addition to the three polyamines. Freshwater/marine unicellular Porphyridium contained putrescine and spermidine, furthermore, spermine was found in some Porphyridium species. In the marine unicellular orders Dixoniellales, Rhodellales and Stylonematales, the presence of putrescine, spermidine, norspermidine, spermine and norspermine was detected. Of the five polyamines, Bulboplastis containing thermospermine instead of spermine, has a novel algal polyamine profile. In the freshwater macroalgal orders Thorelales, Batrachospermales and Compsopongonales, the presence of putrescine, spermidine, homospermidine and spermine was abundant. In red seaweeds belonging to seven orders of the class Bangiophyceae or Florideophyceae, 1,3-diaminopropane, putrescine, cadaverine, spermidine, norspermidine, homospermidine, spermine, norspermine and thermospermine were widely distributed. 1,6-Diaminohexane was distributed within 12 species, aminobutylcadaverine was found in Gelidium and Hypnea, and canavalmine and aminopropylcanavalmine were detected in Meristotheca, as unusual algal polyamines. The distribution of norspermidine and norspermine was particular in marine unicellular species. Homospermidine was a special polyamine member for freshwater multicellular species. 1,6-Diaminohexane and penta-amines were found in seaweeds in addition to common red-algal polyamines. The polyamine profiles of red seaweeds distinguished them from those of green seaweeds (ulvophytes) and brown seaweeds.