General characteristics of Chrysophyta
Division - Chrysophyta:-
General characteristics:-
1. Introduction:-
> Chrysophyta, or golden-brown algae, are common microscopic in fresh water.
> Some species are colorless, but the vast majority is photosynthetic.
> As such, they are particularly important in lakes, where they may be the primary source of food
for zooplankton.
> They are not considered truly autotrophic by some biologists because nearly all chrysophyta become facultatively heterotrophic in the absence of adequate light, or in the presence of plentiful dissolved food. When this occurs, the chrysoplast atrophies and the alga may turn predator, feeding on bacteria or
diatoms.
2. Cell wall:-
> Cellulose wall is lacking.
> The plasma membrane, cytoplasmic membrane show a marked tendency to become silicified.
> Chrysophyceae are characterised by cyst formation and statospore is formed.
> The silica is deposited on the whole surface thus the cell become static (lorica) rigid.
> The cell surface is covered by delicate scales. The scale in chrysophyceae is impregnated with silica and there structure of scale is variable.
> In haptophyceae no silica is formed on the scales. The scale is formed of organic matters.
> Scale may be round and oval the outer surface of which has lattice of cross striation and the inner face has radiating system region.
> Scales are holed and originate out of the secretion of the golgi body but there passes to the surface after its synthesis not exactly known.
3. Cell Membrane:-
> Periplast may be soft and permeable allowing considerable shape changing as in Chromulina verrucose or it may be form of cells having fixed shape.
> The periplast is variously modified in chrysophyceae member. The important modifications of periplast are seen in Coccolithphoridaceae in which the surface layer are gelatinous latter on many calcified disc called coccoliths are formed over the surface.
> The working hypothesis for coccolith formation is that carbon is taken by cell in carbonate form. The molecular CO2 are extracted from the bicarbonate during photosynthesis so that the carbonate remain and was precipitated as coccolith. This requires the supply of ATP which was made available from cyclic photophosphorylation.
> In Mallomonadaceae the surface layer is distinguished into two layers: - outer pectic and inner layer. The chemical nature of which is still in dispute (cellulosic?) The numerous scale with silicified needle are present which help in planktonic existence.
> In the Loricate or Encapsuled form of chryophyceae the protoplast surrounded by a rigid cell envelops and separated by the space. It is believed that such forms made within chrysophyceae and haptophyceae both.
4. Nucleus:- The nucleus status of the cell is simple there is only one nucleus with only one nucleolus. The flagella bases and nucleus are connected. The exact function of this connection is not known. Manton contribute the cytology and Leedale has proposed the connection between flagellum base and nucleus may be mechanical in nature but nothing can be said exact about the mode of division of the nucleus.
5. The contractile vacuole and stigma:-
> The presence of contractile vacuole in the cell is various.
> There may be two simple vacuole located at the anterior end of the cell as seen in Chromulina.
> In Microglena there is a single large vacuole which is surrounded by a number of smaller contractile vacuole. The large vacuole opens to exterior by two canals.
> In Chrysochromalina contractile vacuole is found in only fresh water species and not in marine species. The eyespot is not very wide spread and not detail of its structure is known.
6. Chromatophore:-
> The chromatophore may be single and lobed and two or more parietal chromatophore in cell.
> The form of chromatophore depends on the stage of the life history. For example – the motile stage show saucer shaped chromatophore but the non motile stage chromatophore as stellate.
> The chromatephore revealed the usual structure in which chlorophyll – a, c beta – carotene, Acetylanic carotenoid, Fucoxanthin, diatoxanthin, Diadinoxanthin.
7. Pyrenoids:- Pyrenoids are present in Chromulina and Malomonas and absent in Acromonas Chrysochromolina as a pyrenoid within the chloroplast or chromatophore.
8. Starch absent:- It is not synthesized in chrysophyceae it is not correctly known whether it is functioning equivalent to get in chloroplast or not.
9. Food reserve:- Have been found as glycosides includes:
i. Chrysose:- The food material stored between the wall of the chloroplast and sac of endoplasmic reticulum present around the plastid.
ii. Chrysolaminarin
iii. Leucocin
iv. Oil
10. Reproduction:- It takes place generally by mean of:
i. Fission but isogamous sexual reproduction has been infrequently recorded.
ii. Cyst formation which is characteristic feature of chrysophyceae follows sexual reproduction. Falt (1964) observed cyst can also be formed agamically (without sexual fusion)
Classification:-
Class:- Chrysophyceae
Orders:-
a. Chrysomonadales:-
Sub-orders:-
i. Cromulinae:- Eg.- Mallomonas
ii. Isochrysidineae:- Eg.- Synura
iii. Ochromonadineae:- Eg.- Dinobryon
b. Rhizochrysidales:- Eg.- Chrysamoeba
c. Chrysocapsales:- Eg.- Hydrurus
d. Chrysotrichales:- Eg.- Phaeothamnion
e. Chrysosphaerales:- Eg.- Epichrysis