Dwarf mutants

Some biochemical functions defined by the Arabidopsis dwarf mutants were later confirmed by heterologous expression of genes and by in vivo conversion of postulated substrates [17-20]. As part of these physiological and biochemical studies, tomato cell suspension cultures have also been established to investigate intermediates and enzymes of brassinosteroid biosynthesis and metabolism [21-23]. Enzyme activities from partially purified protein extracts were first detected in this model system [24]. 

Another dwarf mutant of Arabidopsis, sax], defines a step upstream of DWF1 in the brassinosteroid biosynthesis pathway [27]. Rescue experiments with intermediates showed that saxl is involved in the oxidation and isomerization of 3P-hydroxyl,A5 6 precursors to 3-oxo-A4 5 steroids (Fig. (4)). 

Approximately 2 liters of viscous endosperm extracted from immature seed was adjusted to pH 3 by the addition of sulfuric acid. This suspension was extracted directly several times with ethyl acetate. Most of the biologically active material was removed to the ethyl acetate phase, as determined by bioassay with dwarf mutants of maize (8). The combined extracts were concentrated and extracted in turn with 5% aqueous sodium carbonate solution to remove acidic substances. All the biologically active material was removed to the aqueous phase. After this fraction had been acidified to pH 3, it was again extracted with ethyl acetate, which removed the biologically active substances to the ethyl acetate phase. The residue from the ethyl acetate layer (2.5 grams) was then chromatographed on a charcoal-Celite (1 2) column developed with increasing concentrations of acetone in water. 

The dwarf mutant corn (d-1) plants were germinated in soil-vermiculite, transferred when they were nearly ready for bioassay treatment (14), and grown in a growth chamber at about 25° to 30° C. with continuous white fluorescent light of about 450 foot-candles. The roots of the com were supported on filter paper wetted with Hoagland s solution and affixed to slanting glass plates, sup-... 

Seeds of the dwarf mutant com (d-1) were obtained from B. O. Phinney, University of California, Los Angeles. 

Phinney, B.O. (1957). Growth response of a single-gene dwarf mutants in maize to gibberellic acid. Proc. Natl. Acad. Sci. USA 42,185-189. 

Boother, G.M., Gale, M.D., Gaskin, P., MacMillan, J. Sponsel, V.M. (1991). Gibberellins in shoots of Hordeum vulgare. A comparison between cv. Triumph and two dwarf mutants which differ in their response to gibberellin. Physiologia Plantarum 81, 385-92. 

The dwarf mutants of Arabidopsis show, when grown in the dark, many of the characteristics of light-grown plants, including cotyledon expansion, primary leaf initiation, anthocyanin accumulation, and depression of light-regulated gene expression. Involvement of BR in de-etiolation has been discussed.816... 

The partial synthesis from epicandicandiol of some C- and H-labelled kaurene derivatives has been described.These have possible application in the study of the biosynthesis of the Isodon diterpenoids. The syntheses of [17- C]kaur-16-en-20-ol from enmein and of 3-oxygenated derivatives of [17- C]kaur-16-ene from ent-3jS,19-dihydroxy-kaur-16-ene have also been described. The synthesis of radioactive aphidicolin has also been reported. It has been shown ° that ent-kaur-15-ene is formed by the dwarf mutant (ds) of maize in place of ent-kaur-16-ene. 

Ephritikhine, G., Fellner, M., Vannini, C., Lapous, D. and Barbier-Brygoo, H. (1999) The saxl dwarf mutant of Arabidosis thaliana shows altered sensitivity of growth responses to abscisic acid, auxin, gibberellins and ethylene and is partially rescued by exogenous brassinosteroid. Plant., 18,303-14. 

The dramatic stimulation of shoot elongation that occurs in certain dwarf mutants when they are treated with GAs is one of the clearest demonstrations of the importance of these hormones in plant development. This restoration of growth by GA treatment gave the first... 

The dwarf mutants of pea (Ikb) [34] and Arabidopsis dim) [35,36] accumulate 24-methylenecholesterol and isofucosterol and are deficient in campesterol and sitosterol. In the Ikb mutant, the levels of endogenous BRs are significantly reduced. Thus, blocked synthesis of campesterol causes dwarfism by reducing the level of endogenous BRs (Eig. 2). 

As with auxin, both GAs and BRs are involved in cell elongation. One semi dominant GA insensitive mutant gai was identified from a collection of X-ray treated seeds as a leaky dwarf mutant that did not show height increase upon application of bioactive GAs... 

Figure 7. The five mature dwarf mutants and normal maize (Zea mays). The height of the mutants varies from 1/4 to 1/5 that of the normals.

MORI, M., NOMURA, T., OOKA, H., ISHIZAKA, M., YOKOTA, T., SUGIMOTO, K., OKABE, K., KAJIWARA, H., SATOH, K., YAMAMOTO, K., HIROCHIKA, H., KIKUCHI, S., Isolation and characterization of a rice dwarf mutant with a defect in brassinosteroid biosynthesis, Plant Physiol., 2002, 130, 1152-1161. 

---