Page 147 - phytochemistry general program

b. Micronutrient elements These elements are added in relatively minor
concentrations (micromolar concentration) as Fe, Zn, Mn, B, Co and Cu.

2- Organic components

Added to PTC media Organic compounds are also added to plant culture media.
Some of these compounds, such as sugars, are absolutely needed for growth,
while others, such as vitamin and organic acids may not be essential but may

enhance growth.

a. Carbohydrates Most plant tissue cultures are not capable of fixing carbon
through photosynthesis, due to limitation in culture CO2 availability. Therefore,
sugar is added to the medium as an energy source. Sucrose is the most common
sugar added, although glucose, fructose, and sorbitol are also used in certain
instances. The concentration of sugars in nutrient media generally ranges from 20-
40 g/L. Sucrose is somewhat heat-labile, and these autoclaved media actually
consists of a combination of sucrose, D- glucose and D- fructose and this results in
an increase in osomotic potential of the medium. Therefore an autoclaved medium
may give somehow different results compared to a medium containing filter-

sterilized sucrose.

b. Vitamins Vitamin concentrations are generally low as they have catalytic
functions in enzyme systems. Only thiamine (vitamin B1), which is required for
carbohydrate metabolism and the biosynthesis of some amino acids, has been
shown be essential for most plant cultures. Other vitamins are sometimes added to
media formulations. Some of the vitamins are heat-labile, therefore it is always
advisable to filter sterilize vitamin preparations and add them by pipette to the

warm autoclaved medium.

Plant growth regulators (PGRs-phytohormones or plant hormones) .2

A plant hormone can be defined as a small organic molecule that elicits a
physiological response at very low concentrations (<1µm). The correct scientific
description for these molecules is plant growth regulators (PGRs), which have the

following characteristics:

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