Elementary plant Biochemistry and Biotechnology (2+1)

Brassinosteroids

• In 1979, a novel plant growth regulating steroidal substance called brassinolide was isolated from rape (Brassica napus) pollen. More than 24 compounds are known (designated as BR1, BR2). Pollen is the richest source. Brassinosterols are active at concentration much lower (nM to pM range) than those of other types of hormones. Brassinosterols elicit a pronounced stem elongation response in dwarf pea epicotyls, mung bean epicotyls that are sensitive also to gibberellic acids but not auxins. Brassinosteroids are thought by some to be a new class of plant hormones.

The evidences are

• They are widely distributed in the plant kingdom.
• They have an effect at extremely low concentration.
• They have a range of effects which are different from the other classes of planthormones
• They can be applied to one part of the plant and transported to another where in very low amounts elicit a biological response
• They are widely distributed including dicots, monocots, gymnosperms and algae, and in various plant parts such as pollen, leaves, flowers, seeds, shoots and stems


• Among the naturally occurring brassinosteroids, brassinolide and castasterone are considered to be the most important because of their wide distribution as well as their potent physiological activity.