Original - "Heterocyst"
The mechanism of controlling heterocysts is thought to involve the diffusion of an inhibitor of differentiation called patS. Heterocyst formation is inhibited in the presence of a fixed nitrogen source, such as ammonium or nitrate. Heterocyst maintenance is dependent on an enzyme called hetN. The bacteria may also enter a symbiotic relationship with certain plants. In such a relationship, the bacteria do not respond to the availability of nitrogen, but to signals produced by the plant. Up to 60% of the cells can become heterocysts, providing fixed nitrogen to the plant in return for fixed carbon[1].
Edits - "Heterocyst"
Symbiotic Relationships
editAnabaena-Azolla
editA notable symbiotic relationship is that of Anabaena cyanobacteria with Azolla plants. Anabaena reside on the stems and within leaves of Azolla plants[2]. The Azolla plant undergoes photosynthesis and provides fixed carbon for the Anabaena to use as an energy source for dinitrogenases in the heterocyst cells.[2]. In return, the heterocysts are able to provide the vegetative cells and the Azolla plant with fixed nitrogen in the form of ammonia which supports growth of both organisms[2][3].
This symbiotic relationship is exploited by humans in agriculture. In Asia, Azolla plants containing Anabaena species are used as biofertilizer where nitrogen is limiting[2] as well as in animal feed[3]. Different strains of Azolla-Anabaena are suited for different environments and may lead to differences in crop production[4]. Rice crops grown with Azolla-Anabaena as biofertilizer have been shown to result in a much greater quantity and quality of produce compared to crops without the cyanobacteria[3][5]. Azolla-Anabaena plants are grown before and after rice crops are planted[3]. As the Azolla-Anabaena plants grow, they accumulate fixed nitrogen due to the actions of the nitrogenase enzymes and organic carbon from photosynthesis by the Azolla plants and Anabaena vegetative cells[3]. When the Azolla-Anabaena plants die and decompose, they release high amounts of fixed nitrogen, phosphorus, organic carbon, and many other nutrients into the soil, providing a rich environment ideal for the growth of rice crops[3].
The Anabaena-Azolla relationship has also been explored as a possible method of removing pollutants from the environment, a process known as phytoremediation[6]. Anabaena sp. together with Azolla caroliniana has been shown to be successful in removing uranium, a toxic pollutant caused by mining, as well as the heavy metals mercury (II), chromium(III), and chromium(VI) from contaminated waste water[6][7].
References
editMabelz97 (talk) 07:58, 20 November 2017 (UTC)
- ^ Lee, Robert Edward (1999). Phycology (3rd ed ed.). Cambridge, UK ; New York: Cambridge University Press. ISBN 0521630908.
{{cite book}}:|edition=has extra text (help) - ^ a b c d van Hove, C.; Lejeune, A. (2002). "The Azolla: Anabaena Symbiosis". Biology and Environment: Proceedings of the Royal Irish Academy. 102B (1): 23–26. doi:10.2307/20500136.
- ^ a b c d e f Vaishampayan, A.; Sinha, R. P.; Häder, D.-P.; Dey, T.; Gupta, A. K.; Bhan, U.; Rao, A. L. (2001). "Cyanobacterial Biofertilizers in Rice Agriculture". Botanical Review. 67 (4): 453–516. doi:10.2307/4354403.
- ^ Bocchi, Stefano; Malgioglio, Antonino (2010). "Azolla-Anabaenaas a Biofertilizer for Rice Paddy Fields in the Po Valley, a Temperate Rice Area in Northern Italy". International Journal of Agronomy. 2010: 1–5. doi:10.1155/2010/152158. ISSN 1687-8159.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ Singh, S.; Prasad, R.; Singh, B. V.; Goyal, S. K.; Sharma, S. N. (1990-06-01). "Effect of green manuring, blue-green algae and neem-cake-coated urea on wetland rice (Oryza sativa L.)". Biology and Fertility of Soils. 9 (3): 235–238. doi:10.1007/bf00336232. ISSN 0178-2762.
- ^ a b Bennicelli, R.; Stępniewska, Z.; Banach, A.; Szajnocha, K.; Ostrowski, J. (2004-04-01). "The ability of Azolla caroliniana to remove heavy metals (Hg(II), Cr(III), Cr(VI)) from municipal waste water". Chemosphere. 55 (1): 141–146. doi:10.1016/j.chemosphere.2003.11.015.
- ^ Pan, Changchun; Hu, Nan; Ding, Dexin; Hu, Jinsong; Li, Guangyue; Wang, Yongdong (2016-01-01). "An experimental study on the synergistic effects between Azolla and Anabaena in removal of uranium from solutions by Azolla–anabaena symbiotic system". Journal of Radioanalytical and Nuclear Chemistry. 307 (1): 385–394. doi:10.1007/s10967-015-4161-y. ISSN 0236-5731.