The effect of brassinolide on cotton fiber development

Brassinosteroids may represent a sixth class of endogenous plant hormones whose general effect is the stimulation of cell division and elongation in young vegetative tissues. These steroidal lactone compounds act synergistically with auxins in many cases and cooperatively with gibberellic acid (GA3). The requirements for auxins and GA3 in cotton fiber development are well known. Since brassins generally stimulate cell elongation, it may also play a role in cotton fiber development.

Brassinolide (BR), which is the most biologically active of the Brassinosteroids, was used to examine the potential effect of the hormone on cotton fiber development in vitro. Cotton ovules were removed from fiowers post anthesis and floated on liquid media containing various sub-micromolar concentrations of BR. Differential growth rates due to BR treatment were observed. Elongation of fiber was stimulated at 10' M, which was statistically significant. High concentrations of BR (10"^ M) stimulated ovule and callus growth and inhibited fiber development. Subsequently, the ribonucleic acid (RNA) population was isolated and used for northern hybridization with putative BRresponsive and fiber-specific complementary deoxyribonucleic acid (cDNAs) to determine the hormone's effect on the expression of these transcripts. Northern analysis demonstrated the expression of putative BR responsive transcripts in cultured and plant fiber RNA. Brassinolide responsive transcripts illustrated increased expression upon exposure to exogenous BR. Two fiber-specific cDNAs illustrated a partial repression of complementary transcripts upon BR treatment. It is clear that BR plays a role in the stimulation of ovule cell growth, and possesses the ability to regulate gene expression. As a recently recognized endogenous growth regulator with the potential to affect cotton development, BR may be usable to improve commercial cotton production.