Triphasic life cycle of Gracilaria

Plants can be monoecious or dioecious in terms of having male and female gametangia. Gracilaria chilensis is a popular haploid-diploid red algae. It was studied for alterations in basic physiological and demographic parameters related to reproduction. The life cycle of Gracilaria chilensis is a Polysiphonia-type with two free isomorphic generations. Greville introduced the genus Gracilaria in 1830, and it is the third biggest genus in the red algae group, having over 150 species worldwide. Further, the Indian coast has documented around 28 species of Gracilaria.

Also, read: Difference Between Types of Cotton – My Biology Dictionary

Interesting Facts About Gracilaria 

• Gracilaria changii, a red seaweed found in Malaysia, was found to have hypolipidemic effects on high-cholesterol-fed male Sprague-Dawley rats. 5% freeze-dried G. changii powder significantly reduced plasma triglycerides (TC), LDL, and triglycerides (LDL) levels. 10% G. changii powder also reduced triglycerides.
• The treatment also enhances enzyme antioxidant activity. G. changii was found to be as effective as atorvastatin in lowering plasma cholesterol levels.
• Gracilaria can grow in a broad range of salinities, from 5 to 34 ppt. Thus, making it a common seaweed in brackish water, mangrove swamps, and at sea.
• Gracilaria is primarily farmed and collected for agar manufacture, accounting for more than half of the global agar supply.
• Some Gracilaria species contain prostaglandin A2 or E2. They appear to be responsible for a gastrointestinal illness known as “ogonori” poisoning in Japan. Therefore, some typical signs of this poisoning include low blood pressure (hypotension), vomiting, and nausea. Further, it can lead to death due to hypotensive shock.

Meaning of Triphasic Life Cycle of Gracilaria

The triphasic life cycle alternates between two diploid or sporophyte generations. There are two diploid stages and a haploid phase. Red algae have a triphasic life cycle.  They show a triphasic life cycle. Red algae, rhodophyta is one of the oldest groups of eukaryotic algae. The red algae’s peculiar triphasic life cycle is attributed to evolutionary compensation for gamete mobility during division. Further, the supposed occasional incidence of syngamy among their progenitors.

What’s so Wonderful About The Triphasic life cycle of Gracilaria?

• Gracilaria is found all over the world, however, the majority of the species are thought to originate from subtropical and tropical seas. The life cycle of Gracilaria chilensis‘ triphasic has been investigated. It reported the same pattern as P. yezoensis’ triphasic life cycle. which also includes gametophyte formation by apospory.
• The triphasic life history of Gracilaria chilensis has also been connected to the idea of reproductive cost. This means that the several stages of the life cycle developed to optimize resource allocation and survival strategies.
• Gracilaria’s thallus is cylindrical, compressed, or bladelike, with uneven branching that gives it a bushy look. Gracilaria has a typical Polysiphonia-type, or triphasic, life cycle.

Courtsey of Sahu, N., 2004. Studies on Gracilariods From Chilika Lake-Structure Development and Agar Quality (Ph.D. thesis). University of Delhi, Delhi, India.

Stage 1- Gametophyte

Meiosis occurs in tetrasporophytes, producing haploid spores. When liberated, tetraspores attach to the substratum and develop perennial holdfasts. They grow into haploid dioecious males and females. This is the first stage in the life cycle of Gracilaria.

Stage 2- Carposporophyte

After fertilization, a carposporophyte develops on the female haploid plant, and a gonimoblast forms thousands of identical diploid spores. Certainly, the carpospores attached to the substratum develop into perennial holdfasts and tetrasporophytes, completing the complex life cycle.

Stage 3- Tetrasporophyte

Following germination, the carpospores grow into diploid tetrasporophytic plants. Tetrasporophytic plants produce diploid tetrasporangia. Each tetrasporangia produces four tetraspores (n) by meiotic division. They are discharged by breaking the sporangial wall. Two of four tetraspores create male gametophytes while the other two produce female gametophytes. This is the third stage in the life cycle of Gracilaria.

Image source: Mikami, K., Li, C., Irie, R., & Hama, Y. (2019). A unique life cycle transition in the red seaweed Pyropia yezoensis depends on apospory. Communications biology, 2(1), 299.

Diploid spores (carpospores) outlive haploid spores (tetraspores), particularly in locales and periods associated with high biotic and abiotic stresses. Alternation of generations is a kind of life cycle found in plants and algae. Further, successive generations of individuals alternate between haploid and diploid organisms.
Thus it is comparable to sexual reproduction in animals, in which both haploid and diploid cells are found in every generation.

Check out: How to take care of and grow red Hayi gracilaria – YouTube

REFERENCES:

1. Vieira, V.M.N.C.S., Engelen, A.H., Huanel, O.R. et al. Differentiation of haploid and diploid fertilities in Gracilaria chilensis affect ploidy ratio. BMC Evol Biol 18, 183 (2018). https://doi.org/10.1186/s12862-018-1287-x
2. Bast, Felix. (2014). An Illustrated Review on Cultivation and Life History of Agronomically Important Seaplants.