Write the post fertilization stages in rhodophyceae
Answers
The thallus color of Polysiphonia is varied from red to purple.
Ø The red coloration is due to the abundance of the pigment r-phycoerythrin.
Ø Other pigments such as chlorophyll-a, β-carotenes, Xanthophyll and r-phycocyanins are also present.
Learn more: Pigmentation in Algae
Ø The thallus of Polysiphonia consists of two systems:
(1). Prostrate system
(2). Erect system
(1). Prostrate System
Ø The prostrate system is creeping and basal.
Ø It is attached to a suitable substratum.
Ø The attachment is facilitated by well-developed rhizoids.
Ø Each rhizoid is single celled, thick-walled with swollen distal ends.
Ø These swollen distal ends of each rhizoids act as the attachment disc.
Thallus Structure of Polysiphonia
(2). Erect system
Ø The erect system is developed from the prostrate system.
Ø The erect system is vertical and profusely branched.
Ø The thallus of the erect system consists of several parallel filaments called siphons.
Ø The cells of each siphon are placed end to end and are connected by Plasmodesmata.
Ø Each cell of the siphon are genetically related.
Ø There are three types of siphons: (a) Central siphons, (b) Pericentral siphons and (c) Cortical siphons.
(a). Central siphons:
$. The central siphon is located in the center of the thallus.
$. Cells of the central siphon are elongated and comparatively larger.
(b). Pericentral siphon:
$. Peripheral siphon surrounds the central siphon.
$. Cells of the pericentral siphon are developed by the longitudinal division of the central siphon cells.
$. There are 4 – 24 pericentral siphons are present.
$. The number of pericentral siphons varies in different species.
$. The cells of pericentral siphon are comparatively smaller and narrow.
(c). Cortical cells (cortical siphon):
$. The cortical siphon is formed only in the older branches.
$. The cells of the pericentral siphon divide periclinally to produce many cells.
$. These cells are smaller than the pericentral cells.
Ø Plasmodesmatal connections are also present between the cells of central, pericentral and cortical siphons.
Ø Only a single siphon (central siphon) will be present in the apical portion of the thallus.
Ø The thallus of Polysiphonia shows apical growth which is facilitated by an apical cell.
What are Trichoblasts?
Ø Trichoblasts are small mono-siphonous branches of the thallus with limited growth.
Ø Trichoblasts are developed from the apical initial cell.
Ø The apical initial cell undergoes an oblique division to form a trichoblast initial cell.
Ø The trichoblast initial undergoes many rounds of division to form the multicellular, uniseriate and dichotomously branched filaments called the Trichoblasts.
Cell structure
Ø The cells of Polysiphonia possess two-layered cell wall.
Ø The outer layer is pectic and the inner layer is cellulosic.
Ø Each cell is uninucleate with a viscous protoplast.