Abstract
We have recently discovered that brassinosteroids (BRs) can inhibit the growth of etiolated pea seedlings dose-dependently in a similar manner to the ‘triple response’ induced by ethylene. We demonstrate here that the growth inhibition of etiolated pea shoots strongly correlates with increases in ethylene production, which also responds dose-dependently to applied BRs. We assessed the biological activities of two natural BRs on pea seedlings, which are excellent material as they grow rapidly, and respond both linearly and uni-phasically to applied BRs. We then compared the BRs’ inhibitory effects on growth, and induction of ethylene and ACC (1-aminocyclopropane-1-carboxylic acid) production, to those of representatives of other phytohormone classes (cytokinins, auxins, and gibberellins). Auxin induced ca. 50-fold weaker responses in etiolated pea seedlings than brassinolide, and the other phytohormones induced much weaker (or opposite) responses. Following the optimization of conditions for determining ethylene production after BR treatment, we found a positive correlation between BR bioactivity and ethylene production. Finally, we optimized conditions for pea growth responses and developed a new, highly sensitive, and convenient bioassay for BR activity.
Highlights
Brassinosteroids (BRs) are a group of naturally occurring phytohormones with characteristic steroidal structure
Since BRs are present in plants in extremely low concentrations and have potent biological activities, their identification requires highly sensitive bioassays, based on responses to BRs that are not influenced by other endogenous plant hormones
We recently discovered that brassinolide (BL) application has strong effects on etiolated pea seedlings, including all three phenotypic elements of the classical ‘triple response’ to ethylene
Summary
Brassinosteroids (BRs) are a group of naturally occurring phytohormones with characteristic steroidal structure. BRs are essential for plenty of developmental and physiological processes such as cell elongation, cell division, leaf senescence, vascular differentiation, flowering time control, male reproduction, photomorphogenesis, and responses to both biotic and abiotic stresses [1,2,3]. Since BRs are present in plants in extremely low concentrations and have potent biological activities, their identification requires highly sensitive bioassays, based on responses to BRs that are not influenced by other endogenous plant hormones. The gaseous plant hormone with a very simple structure consisting of two carbon and four hydrogen atoms, is produced in most plant tissues and cell types. Crucial processes in plants, such as seed germination, growth, apical hook formation, organ senescence, fruit ripening, abscission, gravitropism, and stress responses, are affected by this hormone [5,6]. The most known effect of ethylene on etiolated seedlings is called a ‘triple response’, which consists of inhibition of stem elongation, radial swelling of the stem, and impairment of the normal geotropic response
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