Biological World

  Q.Distinguish between Pr and Pfr form.                   Pr form             Pfr form 1. It is an inactive form of phytochrome.   2.Being inactive, it does not show phytochrome mediated response.   3.Absorption maxima of it is in red wave region (about 680 nm).   4.It is found diffused throughout the cytosol.     5.It is converted to Pfr form in presence of    red light.   6.On centrifugation (2000Xg) it remains present    in the supernatant.   7.It shows less activity    in presence of urea, metal ions etc. 1. It is an active form of phytochrome.   2.Being inactive, it show phytochrome mediated response.   3.Absorption maxima of it is in far red wave region (about 730 nm).   4.It is usually found in discrete areas of cytosol.   5.It is converted to Pr form in presence...

WATER STRESS IN PLANT Water stress is known to be one of the major constraints of agricultural productivity as most of the cultivation of our country is based on rain fed irrigation. Just as water scarcity leads to stress in plants, excess water is also a potential cause of stress. Excess water or water logging is mainly caused due to improper drainage and cultivation in low lying areas. Cultivation of maize is often seriously hampered by water logging conditions and the plant responds to this stress by an alternation of its metabolic processes. Under water logging condition, the most common and immediate injury symptom was leaf yellowing that initiated from the base of the plants and proceeded towards the tip (Barnwal  et al ., 1999). With severity longevity of the stress condition, the yellow leaves get necrotic spots and finally the leaves along with leaf sheath get dried. Quantification of this response was undertaken in the present study, which clearly showed that the stress c...

ভাইরয়েডস (Viroids) 1970 খ্রিস্টাব্দের আগে পর্যন্ত ভাইরাসকেই সর্বাপেক্ষা ক্ষুদ্রতম সংক্রামক বস্তু (infection agent) হিসাবে চিহ্নিত করা হতাে। পরবর্তীকালে ভাইরয়েড (viroids)-এর আবিষ্কার পূর্বোক্ত ধারণার পরিবর্তন ঘটায়। দেখা যায় ভাইরাসের থেকেও ক্ষুদ্রতম কোনাে বস্তু জীবদেহে রােগের সৃষ্টি করতে পারে। ক্যাপসিড বিহীন, কেবলমাত্র একটি নগ্ন RNA দ্বারা গঠিত, ভাইরাসের থেকেও ক্ষুদ্র যে সংক্রামক বস্তু জীবদেহে রােগ সৃষ্টি করে, তাকে ভাইরয়েড বলে। থিওডর ওট্রো ডায়েনার (Theodor Orto Diener) এবং ডাবলিউ. বি. রেমার (WB Raymer) 1971 সর্বপ্রথম আলুর রােগসৃষ্টিকারী পটাটো স্পিন্ডিল টিউবার ভিরিওয়েড বা PSTV (Potato Spindle Tuber Vinoids) আবিষ্কার করেন।   ভাইরয়েডের বৈশিষ্ট্য   [i] ক্যাপসিডবিহীন এবং নগ্ন RNA (naked RNA) দ্বারা গঠিত। [i] সংক্রামক RNA খুবই কম আণবিক ভরসম্পন্ন (low molecular weight) হয়। [ii] রােগাক্রান্ত কোশের (susceptible cells) মধ্যে ভাইরয়েড নিজেই স্বয়ংক্রিয়ভাবে প্রতিলিপি গঠন করতে পারে (কোনাে সাহায্যকারী ভাইরাস ছাড়াই)। [iv] সংক্রামক RNA-তে কোনাে প্রােটিন কোডিং জিন (protein coding gene...

What is southern blotting? Schematically present the procedure of this technique. Discuss the importance of this technique in DNA finger printing.  Southern Blotting :-        Southern blotting is a method developed by a molecular biologist E.M. Southern 1975 for analysing the related genes in a DNA restriction fragment. This is a procedure for transfer of denature DNA from an agarose its hybridisation with a complementary radiolabelled  nucleic acid i .e. Probe. Procedure of southern blotting :-        Blotting is an effective and sensitive procedure to provide a physical map of restriction site within a gene located normally on a chromosomal and reveal the number of copies of gene in the genome and the degree of similarly of the gene when compared with other complementary genes. This is achieved by this method in which the following steps are performed. ( i ) 1 st  of all the sample DNA is subjected to mechanical shearing or restr...

  Polymerase Chain Reaction:                            PCR stands for the Polymerase Chain Reaction. It is a patented procedure developed by Kary Mullis in 1987, which can enzymatically amplify minute quantities of DNA to large number of copies. By this method, a single copy of a nucleic acid that is often difficult to detect by standard hybridization methods, is multiplied to ≥10 7 copies in a short period.        Mechanism of PCR:                              In 1985-86 a major development occurred at Cetus Corporation, USA where researchers develop an in vitro method for the amplification of DNA fragment. This method is known as polymerase chain reaction (PCR). The techni...