Karenia Brevis
Uploaded by kutiekay on Apr 04, 2013
Karenia brevis usually reproduce by asexual process, dividing into two cells, then into four and so on. Firstly, cysts of the karenia brevis lay on the ocean floor and might stay in the ground for years, without being disturbed. Oxygen and other conditions, such as the right temperature and pressure are essential for the beginning of the germination process. When the temperature increases, as well as the light absorbsion, the cyst breaks open and a swimming cell appears to the ocean. After a few days time the cell reproduces by simple division and as a result hundred of cells will reproduced within weeks, having the same number of chromosomes in the nucleus.
However, is really important to mention that karenia brevis might have sexual reproduction and a new life change and that happens only when the organism cannot have access in available nutrients, thus growth stops and gametes are formed. During gametogenesis the chromosomes in the nucleous reassume a typical dinokaryotic appearance, the nuclear envelope appears in all mitotic stages and the mitotic spindle is extracellular. Spindle microtubules pass through furrows and tunnels that form in the nucleus at prophase (Dodge 1987). Some microtubules contact the nuclear envelope, lining the tunnels at points where the chromosomes also contact. The chromosomes usually have differentiated, dense regions inserted into the envelope. After that, the two cells (gametes) join together. Syngamy involves equal motile gametes and is called isogamy. Then, the formed cell develops into a zygote by homothallism, which is the gamete fusion in clonal strains. The product of gamete fusion is a planozygote, which may remain motile for hours or a few days. Eventually a non-motile thick-walled resting cyst (hypnozygote) is formed. Excystment occurs after a varying length of time of inactiveness. Meiosis is heralded by a peculiar churning and rotation of the nucleus, a process called nuclear cyclosis associated with the pairing of homologous chromosomes .Meiosis may occur before or after the encystment and is normally accomplished in two successive divisions. The mobile zygotes follow the long-term encystment (resting cysts). The inactive cysts fall into the bottom of the ocean until the time is appropriate for another germination (Mona Hoppenrath and Juan F. Saltarriaga, 2008).
Many scientists have done research about the life cycle of Karenia brevis in order to find out if is connected with the main effects of red tides in humans and animals. Karen...