which one of the following is basic nutrient medium which induces the differentiation of embryo and plantlets from various plant tissue?
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Answer:
During plant tissue culture growth sucrose acts as a fuel source for sustaining photomixotrophic metabolism (organisms can use different sources of energy and carbon), ensuring optimal development, although other important roles such as carbon precursor or signaling metabolite have more recently been highlighted. Sucrose is a very important part of nutrient medium as an energy source, since most plant cultures are unable to photosynthesize effectively owing to poorly developed cellular and tissue development, lack of chlorophyll, inadequate gas exchange and carbon dioxide in tissue culture vessels, etc. Hence, they lack auxotrophic ability and need external carbon for energy. Sugar uptake in plant tissue cultures appears to be partially through passive permeation and partially through active transport. Sucrose also supports the maintenance of osmotic potential (osmoticum) and the conservation of water in cells. Hence, in anther culture a higher concentration of sucrose (6–12%) is used. It has been also proven that plant tissue cultures do not fix enough CO2 to sustain growth in the absence of sucrose, mainly due to limited CO2 inside the vessel. However, high sucrose concentration in the media restricts the photosynthetic efficiency of cultured plants by reducing the key enzymes for photosynthesis, levels of chlorophyll, and epicuticular waxes promoting the formation of structurally and physiologically abnormal stomata. The most preferred carbon or energy source is sucrose at a concentration of 20–60 g/L. But the levels of sucrose that are normally used to support the growth of tissue cultures are often inhibitory to chlorophyll synthesis. During autoclaving the medium sucrose is hydrolyzed to glucose and fructose, which are then used by the plant material for their growth. Fructose, if autoclaved is toxic. It has been found that a plant tissue culture medium containing glucose or fructose sterilized by autoclaving inhibits the growth of carrot root tissue cultures. More growth inhibition occurs when sugar and culture medium is autoclaved together [237]. Other mono- or disaccharide and sugar alcohols like glucose, sorbitol, raffinose, etc., may be used depending upon plant species. Sucrose is still the best source of carbon followed by glucose, maltose, and raffinose; fructose was less effective and mannose and lactose were the least suitable. Carbohydrate sucrose is generally required to be present in addition to IAA before tracheid elements are differentiated in tissue cultures. Different types of sugars and their different roles in growth and development of plant cell are mentioned Table 2.12.
Explanation: