• Bulletin of the Korean Chemical Society
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• v.24 no.10
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• pp.1541-1543
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• 2003

• Journal of Plant Biotechnology
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• v.30 no.4
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• pp.411-419
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• 2003

The potent biosynthetic precursors, 24$\alpha$-methylcholesterol and 24$\alpha$-methylcholestanol, and the endogenous brassinosteroids (BRs), castasterone (CS) and 6-deoxocastasterone (6-deoxoCS), were identified from shoots of maize seedlings. In addition, the presence for activities of several enzymes involved in the late C6-oxida-lion pathway from 24$\alpha$-methylcholestanol to CS was demonstrated in the plants. However, activity for brassinolide (BL) synthase which catalyze the conversion of CS to BL, the last step of the late C6-oxidation pathway, was not detected in the enzyme solution obtained from the maize shoots. Together with the fact that BL was not identified from the maize shoots, these results strongly suggested that BRs in the maize shoots are biosynthesized during seedling growth and the active BR in the shoots is not BL but CS.

• Journal of Plant Biotechnology
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• v.33 no.1
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• pp.65-73
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• 2006

Regulatory mechanism for endogenous levels of castasterone (CS) and its biosynthetic precursors in shoots of maize was investigated by the use of enzyme solution prepared from the plant tissue. When [$^2H_0$]- and [$^2H_6$]-CS was used as substrates, [$^2H_0$]-26-norCS and [$^2H_3$]-28-norCS were identified as products, indicating that [$^2H_0$]- and [$^2H_6$]-CS are differently metabolized into [$^2H_0$]-26-norCS and [$^2H_3$]-28-norCS by C-26 and C-28 demethylation, respectively. This suggests that both C-26 and C-28 demethylation can be involved in CS catabolism. In fact that C-28 demethylation only occurred when isotope labeled substrate was used, however, C-26 demethylation is thought be a natural reaction occurred in the maize shoots. When 6-deoxoteasterone (6-deoxoTE) was used, 6-deoxo-26-norTE and 3-dehydro-6-deoxo-26-norTE as well as 6-deoxo-3-dehydroTE and 6-deoxotyphasterol (6-deoxoTY) were identified as enzyme products. When 6-deoxoTY was added, 6-deoxo-26-norTY as well as 6-deoxo-3-dehydroTE and 6-deoxoTE was identified as products. These indicate that C-26 demethylation of 6-deoxoTE, 6-deoxo-3-dehydroTE and 6-deoxoTY as well as a reversible C-3 epimerization from 6-deoxoTE to 6-deoxoTY intermediated by 6-deoxo-3-dehydroTE are operative in the maize shoots, demonstrating that endogenous levels of biosynthetic precursors of CS are also controlled by C-26 demethylation. Therefore, it is thought that C-26 demethylation is an important and a common deactivation process which functions to maintain steady state levels of endogenous brassinosteroids in the maize shoots.