Life Cycle Of Pithium BSc 1st Year Botany Notes
Life Cycle Of Pithium BSc 1st Year Botany Notes :- This post will provide immense help to all the students of BSc Botany 1st Year All PDF Free Download All Notes Study Material Previous Question Answer . You will get full information Related to BSc Botany in over site. In this post I have given all the information related to BSc Botany Completely.
प्रश्न 15 – पिथियम के जीवन–चक्र का रेखांकित चित्र बनाओ।
Hyphal Structure of Pythium:
Generally it is held that the hyphal wall contains cellulose. According to Mitchell and Sabar (1966) and Bartnicki – Garcia (1966), cellulose is a minority component or even lacking altogether Monocha and Colvin (1968) also could not detect the presence of cellulose in the Phythium hyphal wall.
B glucans is the predominant material. Mature hyphal wall is differentiated into two distinct layers which differ in the arrangement of microfibrils.
The outer layer contains randomly dispersed micro-fibrils and the inner has longitudinal arrangement. The microfibrils give reflections different from cellulose I or chitin.
Within the hyphal wall is the plasma membrane which forms lomasomes. The plasma membrane encloses the hyaline cytoplasm which becomes vacuolate in the older plants. The hyphal cytoplasm contains numerous small randomly dispersed nuclei, mitochondria and dictyosomes.
The endoplasmic reticulum, and cytoplasm ribosome are abundant and in the young hyphae. The reserve food is in the form the glycogen and there oil globules in addition. In the presence of lomasomes and dictyosomes, Pythium resembles green algae more than any other member of Mycota.The hyphal growth is by apical extension.
Reproductive Phase in Pythium:
The reproductive phase sets in much before the death of the host seedling. Reproduction is both asexual and sexual.
Asexual Reproduction (Fig. 6.18 B-H):
It takes place by means of zoospores which are produced in small, globular or oval, sac-like sporangia. The sporangia are formed singly and terminally at the ends of somatic hyphae which project into the damp atmosphere from the mycelium within the host tissue (B). There are no specialized sporangiophores.
The sporangia measure 15- 26 microns in diameter. Sometimes the sporangia are intercalary (I) The high humidity in the air promotes the growth of the fungal mycelium and the production of zoospores. Each sporangium is a multinucleate structure.
It is separated from the rest of the hypha, which still retains the power of elongation, by means of a transverse septum. The sporangiam is pushed aside and the hyphal tip grows to form the second sporangium. The sporangium is filled with hyaline cytoplasm containing numerous nuclei. It is slightly denser than that of young somatic hyphae.
(a) Indirect Germination of Sporangia (Fig. 6.18):
Under wet conditions sporangia remain attached to the hyphae bearing them. They function as zoosporangia. The mature zoosporangium puts out from its side or at its apex a narrow, papilla-like outgrowth (C).
It is tubular at first and called the exit tube. The apex of the exit tube swells up into a thin-walled, tiny, balloon-like vesicle (D) The contents of the zoosporangium by now have divided into a small number of uninucleate, daughter protoplasts.
These migrate into the vesicle through the exit tube and become metamorphosed into zoospores. According to some, the undifferentiated protoplast of the zoosporangium migrates through the exit tube into the vesicle where differentiation of zoospores takes place.
The zoospores when mature, exhibit rocking motion and bounce on the vesicle wall. Consequently the vesicle suddenly bursts. The exit tube may often persist after the rupture of the vesicle.
The released zoospores swim and scatter in all directions (E). The tinsel flagellum is directed forward and the longer whiplash trails behind when the zoospore is in motion in the thin film of water on the host surface or in the soil.