Spirogyra is a filamentous type of algae found in freshwater habitats. Two of the most interesting spirogyra facts are presence of spiral shape chloroplasts and reproduction by conjugation method.
Spirogyra is a green algae having a filamentous structure, which measures about 10-100 micrometer in width. The length of the filament is long and may stretch up to several centimeters. Believe it or not, more than 400 species of spirogyra algae are identified from freshwater habitats. One of the distinctive facts is the presence of spiral or helical shaped chloroplast visible under microscope, hence the name. This characteristic feature is used as an identifying attribute for spirogyra genus.
Spirogyra Algae Facts
A stretch of spirogyra filament contains cylindrical or sub-cylindrical cells, that are arranged in a linear fashion. You can spot green masses of spirogyra in eutrophic (nutrient rich) freshwater bodies. Under heavy growth, they form large, slimy, stingy green mats that float on the surface of water. At times, air bubbles are trapped between the masses, which reveals increased rate of photosynthesis and higher production of oxygen. Such cases are observed under favorable environmental conditions.
As per taxonomical classification, spirogyra kingdom is Protista, which is represented by diverse organisms having simple cellular organization. It belongs to phylum, Charophyta (a group of green algae) and class Zygnematophyceae. Having a filamentous, septate body, spirogyra family is Zygnemataceae and order is Zygnematales (or Conjugales) and the scientific name is Spirogyra sp., as species name vary according to the particular type.
Nearly all the cells of spirogyra are identical to each other. They are protected by two layers of cell wall; an outer cellulosic layer and inner pectin layer. A large vacuole occupies most of the cell space. The nucleus is located at the center, which is suspended in the cell with the help of protoplasmic strands. In the ribbon-like chloroplasts, pyrenoids are positioned at regular intervals.
Spirogyra can reproduce by both asexual and sexual means. In the former type, the filament undergoes fragmentation resulting in numerous filaments. With cell enlargement and subsequent mitosis, each fragment grows and develops into a mature filament. This is a typical method of reproduction in spirogyra. Another amazing thing about these creatures is their mode of sexual reproduction, called conjugation.
With reference to the process, spirogyra conjugation is of two types – scalariform and lateral. In the former type, two compatible filaments come together and align side by side. Following this bulges are created, which grow further till they touch each other. The middle cell wall is dissolved leading to formation of a conjugation tube. Consequently, a conjugation canal is formed through which protoplast of one cell (containing male gamete) is transferred to the other cell (containing female gamete) and a diploid zygote is formed.
Formation of conjugation tubes till development of zygotes happen at the same time in many cells of the adjacent filaments. Very often, one strand contains empty cells after fertilization, while the other strand encases zygotes. In contrary to scalariform conjugation, lateral type takes place by formation of a curved conjugation tube in the same filament. Over here, two cells in the same filament undergo fertilization to form zygote. The zygote then converts to zygospore by forming a thick, protective cell wall.
Coming to spirogyra life cycle, it comprises haploid adult cells. In fact, the cylindrical cells assembled in the form of filaments are haploid. After fertilization, zygospores are released into the surrounding environment, which remain dormant in harsh conditions. With the arrival of favorable conditions, a zygospore undergoes meiosis, resulting in four haploid cells. Out of these, a single cell grows into a new spirogyra filament.
So, this was a brief overview regarding spirogyra facts. You can observe conjugation tubes formed between two adjacent strands under a microscope. As mentioned already, increased growth of spirogyra is a warning sign for eutrophic condition of the water body. Hence, it is often considered as a weed for ponds and lakes.