Structural and biosynthetic relationships of BRs to sterols

Generally the most abundant sterol in higher plants is sitosterol which has a 24a-ethyl (Table 1), which accounts for about 50 to 80% of the total amount of plant sterols [16]. However, only seven species of 39 plants hitherto examined have been known to contain BRs with a 24a-ethyl and these are not major BRs except in the green alga Hydrodictyon reticulatum [18] (Tables 1 and 2). Furthermore, immature seed of Phaseolus vulgaris contains sitosterol as the major sterol (56% of the total sterol), however, corresponding BRs (28-homocastasterone and related BRs) were detected at very low levels [19]. On the other hand, campesterol and 24-methylene-25-methylenecholesterol each accounts for only about 3% of the total sterols. However, castasterone and 25-methyldolichosterone (and related BRs), which structurally correspond to these sterols, respectively, are major 

BRs in this tissue [20], Therefore, biosynthetic enzymes of BRs in P. vulgaris seeds can utilize preferentially campesterol and 24-methylene-25-methylenecholesterol rather than sitosterol. Although BRs related to 24-methylene-25-methylenecholesterol were only 

Structural correlation of brassinosleroids with sterols and distribution of brassinosteroids 

Ri Cholesterol (C27) pY k° 28-Nurcastasterone VsY Rs 28-Norbrassinolide Zea mays llen) [21] Omithopus sativus ( oot)f22] Lycopercicon esculentim (shoot) [23] (10 species) 

24-methylenecholesterol (C2g) Dolichosterone OH 1 Ra Uolicholide Dolictuis lahlab (seed) [26] Cryptomeria japonica pollen) [27] Phaseolus vulgaris (seed) [28,64] (5 species) 

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