A cutting-edge finding has been unveiled by researchers in the rapidly rising field of cellular biology: the unknown organelle “nitroplasts”, which are located within algal cells and are essential to nitrogen metabolism. Algae, known to many as the “green engines” of the planet, drive a substantial portion of the Earth’s oxygen supply and form the foundation of countless aquatic feed chains. Nevertheless, the intricate puzzle of algal cells has kept most cellular processes concealed from the eye of which far-reaching issues of cellular metabolism and the health of aquatic ecosystems remain to be solved.
Recently, a group of scientists from the University of Cambridge has identified something called nitroplast – a specialized organelle responsible for storing and processing nitrate, which is essential for algal nourishment and metabolism. How did this discovery happen? It all started with observation and microscopy. During the process of visual examination of different algal species such as green algae and diatoms using contemporary imaging techniques, the researchers observed structures with clearly defined membranes.
A light micrograph of B. bigelowii. Marked arrow shows the nitroplast. (Credit: Tyler Coale/UCSC)
Originally, these “vacuoles” were believed to be nutrient storage organelles. Nevertheless, later work on the phenotypes of nitrate uptake and storage mutants would essentially show that these organelles were involved in the active uptake, storage, and metabolism of nitrate, which is the critical nitrogen source for algal growth and development. Nitrogen is an essential macronutrient for all living organisms. Therefore, its availability dictates the productivity and distribution of algal blooms in any aquatic ecosystem. Most literature suggests that nitrate assimilation occurs in the cytoplasm of algal cells. However, the discovery of nitroplasts seems to challenge the argument. These newly identified organelles act as specialized compartments that concentrate and store nitrate, protecting the cell from potential toxicity. Moreover, nitroplasts harbor a suite of enzymes responsible for converting nitrate into ammonium, a form readily usable by the cell’s metabolic processes.
Way to Nitroplast
It took a while for scientists to find their way to the nitroplast. In 1998, Zehr discovered a short DNA sequence from something akin to an unknown nitrogen-fixing cyanobacterium floating in the Pacific Ocean seawater. He and his colleagues have been laboring on the newly found shell, which they later dubbed UCYN-A through 2001 Additionally, Kyoko Hagino, at Kochi University in Japan, was putting in great effort into growing a marine alga in culture, which eventually happened to be the host of UCYN-A. After more than 300 sampling voyages and more than a decade of efforts, Hagino managed to cultivate the alga in culture. This enabled other researchers to bring the suspicious cyanobacterium UCYN-A and its marine-alga alpha in the lab to analyze together.
Crowning nitroplast as an organelle.
The Species of the marine haptophyte algae Braarudosphaera bigelowii harbor the N2-fixing endosymbiotic cyanobacteria UCYN-A, which might be evolving organelle-like characteristics. Initially, scientists considered UCYN-A as an endosymbiont closely associated with an alga. However, the two recent papers suggest that UCYN-A has co-evolved with its host beyond symbiosis and now meets the criteria for an organelle.
What’s next for nitroplast
Current scenario needs further research on the evolutionary roots of nitroplasts origins, factors of their distribution between different species of algae, and the hereditary pathways that regulate their development and performance. In addition, comparative research of plant species with and without nitroplasts will help establish what advantages these organelles give as a product of organic evolution. The study of nitroplasts will assist in understanding the complex scope of correlation between the sorts of metabolism conducted inside cells of algae and the configuration, performance of the cellular organelles.