Totipotency and Dedifferentiation

पूर्णशक्तता व विविभेदन (Totipotency and Dedifferentiation):-

पूर्णशक्तता (Totipotency):-

·  Gottlieb Haberlandt ने पूर्णशक्तता की खोज की थी। इन्हें पादप ऊत्तक संवर्धन का जनक भी कहा जाता है।

(Totipotency was discovered by Gottlieb Haberlandt. He is also called as father of plant tissue culture.)

·  ‘Totipotency’ शब्द T. H. Morgan के द्वारा दिया गया था।

(The term 'totipotency' was given by T. H. Morgan.)

·  परिभाषा (Definition):- 

“एकल पादप कोशिका की सम्पूर्ण पादप के निर्माण की क्षमता को पूर्णशक्तता कहते हैं।”

("The ability of a single plant cell to develop into an entire plant is called totipotency.")

अथवा (or)

“एकल पादप कोशिका की किसी भी प्रकार की कोशिका में विभेदित होने की क्षमता को पूर्णशक्तता कहते हैं”

("The ability of a single plant cell to differentiate into any type of cell is called totipotency.")

Ø  प्रथम परिभाषा के अनुसार जाइगोट में पूर्णशक्तता होती है।

(According to the first definition, the zygote has totipotency.)

Ø  द्वितीय परिभाषा के अनुसार अन्य कोशिकाओं में भी पूर्णशक्तता होती है।

(According to the second definition, other cells also have totipotency.)

·  जन्तु स्टेम कोशिकाएं (Animal Stem Cells):- ये कई प्रकार की कोशिकाएं उत्पन्न करती हैं परन्तु सभी प्रकार की कोशिकाओं को उत्पन्न नहीं कर सकती। इन्हें ‘Omnipotent’ कहा जाता है। अत: जन्तुओं के लिए कभी भी पूर्णशक्तता शब्द का उपयोग नहीं किया जाता है।

(They produce many types of cells but cannot produce all types of cells. These are called 'Omnipotent'. Therefore, the term totipotency is never used for animals.)

·  सभी या अधिकांश पादप कोशिकाएं पूर्णशक्त होती हैं। एकल पादप कोशिका या कर्तोतक से सम्पूर्ण पादप को विकसित किया जा सकता है।

(All or most of the plant cells are totipotent. The whole plant can be developed from a single plant cell or an explant.)

·  एकल पूर्णशक्त कोशिका से सम्पूर्ण पादप के पुनरुद्धभवन को 2 मुख्य मापदण्ड पूर्ण करने चाहिए –

(Regeneration of the whole plant from a single totipotent cell should fulfill 2 main criteria -)

i. यह एकल कोशिका से प्रारम्भ होना चाहिए क्योंकि पूर्णशक्तता एक कोशिकीय शब्द है।

(It must begin from a single cell because totipotency is a unicellular term.)

ii. यह एकल प्रक्रिया के रूप में पूर्णतया स्वायत होना चाहिए।

(It should be completely autonomous as a single process.)

विविभेदन (Dedifferentiation):-

·   परिभाषा (Definition):- इस प्रक्रिया में परिपक्व व विभेदित कोशिकाएं अपनी पहचान को खो देती हैं तथा आद्य या प्रारम्भिक कोशिकाएं बन जाती हैं और इनमें विभाजन की क्षमता विकसित हो जाती है।

(In this process, mature and differentiated cells lose their identity and become primordial or initial cells and develop the ability to divide.)

·   यह कोशिकाओं की विकासात्मक क्षमता को बढ़ाता है।

(It increases the developmental efficiency of cells.)

·   यह विभेदन का प्रत्यावर्तन (विपरीत प्रक्रिया) होता है इसलिए एक ही कोशिका वंशावली में हो सकता है।

(It is the reversion of differentiation so can occur in the same cell lineage.)

·  यह उन सभी प्रक्रियाओं के लिए उपयोग किया जा सकता है जो कोशिकीय क्षमता को बढ़ाती हैं।

(It can be used for all processes that increase cellular efficiency.)

·   सभी बहुकोशिकीय जीवों में जीनों की संख्या निश्चित होती है। परन्तु इनकी कोशिकाएं सभी जीनों को अभिव्यक्त नहीं करती हैं। बल्कि जीनों के एक भाग को ही अभिव्यक्त करती हैं। ऐसी कोशिकाओं को आनुवंशिक रूप से विभेदित कहते हैं।

(All multicellular organisms have a fixed number of genes. But their cells do not express all genes. Rather they expresses only a part of genes. Such cells are called genetically differentiated.)

·  आनुवंशिक रूप से पूर्णतया विभेदित कोशिका जीनोम में कोड किए सभी जीनों को अभिव्यक्त करेगी। ऐसी कोशिका का वास्तव में अस्तित्व नहीं होता है।

(A genetically fully differentiated cell will express all genes coded in the genome. Such a cell does not really exist.)

·  जाइगोट में 2 गुण होते हैं –

(Zygote has 2 properties -)

i. उच्च विकासात्मक क्षमता

(High developmental potential)

ii. अच्छी तरह से परिभाषित जीन अभिव्यक्ति पैटर्न

(Well defined gene expression pattern)

अत: जाइगोट को सबसे कम विभेदित या विविभेदित माना जाता है।

(Hence the zygote is considered to be the least differentiated or dedifferentiated.)

·  उसी प्रकार (Similarly):-

Ø  Stem cells कम विभेदित या विविभेदित होती हैं।

(Stem cells are less differentiated or dedifferentiated.)

Ø  कायिक कोशिकाएं अधिक विभेदित होती हैं।

(The somatic cells are more differentiated.)

Ø  इस प्रकार stem cells कायिक कोशिकाओं की तुलना में कम विभेदित होती हैं।

(Thus stem cells are less differentiated than somatic cells.)

·  उच्च विकासात्मक क्षमता होने के बावजूद भी Stem cells विभेदित भी होती हैं।

(Stem cells are differentiate too despite having a high developmental capacity.)

·  पादप की प्ररोह व मूल की विभज्योत्तक कोशिकाएं पूर्णशक्त होती हैं।

(The meristematic cells of the shoot and root of the plant are totipotent.)

·   जंतुओं की भ्रूणीय Stem cells बहुशक्त होती हैं।

(Embryonic Stem cells of animals are pluripotent.)

·   पादपों में विविभेदन कैलस निर्माण से संबन्धित होता है। वृद्धि कर रही विविभेदित कोशिकाओं के समूह को कैलस कहते हैं।

(Differentiation in plants is related to callus formation. A group of growing differentiated cells is called a callus.)