COTTON;(Bt cotton);-

Saying that “Cotton is an important cash crop for Pakistan” would be an understatement. It accounts for 8.2 per cent of the value added in the agriculture sector and about 2% to GDP, adds over $2.8 billion to the national economy.Bt Cotton first introduced in 1996 in the United States and Australia has since then proved to be an important tool to control chewing pests.Bacillus thuringiensis (or Bt) isGram-positive, soil-dwelling bacterium, commonly used as a pesticide. Additionally, B. thuringiensis also occurs naturally in the gut of caterpillars of various types of moths and butterflies, as well as on the dark surface of plants.

There are several advantages in expressing Bt toxins in transgenic Bt crops:
The level of toxin expression can be very high thus delivering sufficient dosage to the pest.
The toxin expression is contained within the plant system and hence only those insects that feed on the crop perish.
The toxin expression can be modulated by using tissue-specific promoters, and replaces the use of synthetic pesticides in the environment. The latter observation has been well documented world-wide.

Bt-modified crops appear to be safe for farmers and consumers. The proteins produced by Bt have been used in sprays in farming techniques for many years with seemingly no ill effects on environment or human health.

Bt toxins are considered environmentally friendly by many farmers[who?] and may be a potential alternative to broad spectrum insecticides. The toxicity of each Bt type is limited to one or two insect orders, and is nontoxic to vertebrates and many beneficial arthropods. The reason is that Bt works by binding to the appropriate receptor on the surface of midgut epithelial cells. Any organism that lacks the appropriate receptors in its gut cannot be affected by Bt.[20][21

Limitations of Bt crops;
Kenyans examining insect-resistant transgenic Bt corn.
Constant exposure to a toxin creates evolutionary pressure for pests resistant to that toxin. Already, a Diamondback moth population is known to have acquired resistance to Bt in spray form (i.e., not engineered) when used in organic agriculture.The same researcher has now reported the first documented case of pest resistance to biotech cotton.

One method of reducing resistance is the creation of non-Bt crop refuges to allow some non-resistant insects to survive and maintain a susceptible population. To reduce the chance that an insect would become resistant to a Bt crop.

BIOTECHNOLOGY IN BOTANY:,
It is the latest branch of branch of botany, in which we deals with the bioengineering in plant physiology , for the good yield of plants, get more benefits from plants, and bring good development of plants..Biotechnology, which allows the transfer of a gene for a specific trait from one plant variety or species to another, is one important piece of the puzzle of sustainable developmentPlant biotechnology offers the potential to produce crops that not only taste better but are also healthierPlant biotechnology is an extension of this traditional plant breeding with one very important difference -- plant biotechnology allows for the transfer of a greater variety of genetic information in a more precise, controlled manner.Modern techniques of genetic engineering are essentially a refinement of the kinds of genetic modification that have long been used to enhance plants, micro-organisms, and animals for food. The products of the newer techniques are even more predictable and safer than the genetically engineered foods that have long enriched.MicroRNA biogensis & fuction in higher plant;plant responses to environmental conditions has confirmed the versatile roles of miRNAs as a key component of plant molecular biology.
TISSUE CULTURE
Its gerenally the accepted the term ''TISSUE CULTURE'' refers to the in vitro cultivation of all plant part,wether a single cell or tissue or a organ, underr aseptic conditions. The principles involve in tissue culture are very simple