Studies on the physiology of dwafism in wheat (T.aestivum L.) VII. Endogenous and GA₃ induced IAA-like substances

V. KUMAR^* and B.D.BAIJAL

Agra College, Agra - 282002, India

Dwarf mutants of several plant species have often been regarded deficient in some aspect of growth hormones. Since the classical work of VAN OVERBEEK (1935) who observed that the dwarf maize mutants either destroyed more IAA or produced less of it, a number of workers have emphasised the importance of auxins in dwarf plants (NAKAYAMA 1941). Discovery of gibberellin proved to be a turning point and several workers proposed that GA₃ controls plants growth via auxin metabolism (PALEG 1965). In fact, increased auxin levels in GA treated tissues of tall as well as dwuf plants have been reported by KOGL & ELEMA (1960) and several others.

Auxin-like content have been found to be higher in tall cultivar of wheat in comparison to their dwarf counter parts (BHARDWAJ & DUA 1974). The authors reported higher gibberellin-like substances in certain dwarf varieties of wheat (KUMAR & BAIJAL 1986) and therefore it was imperative for us to examine endogenous IAA-like substances as also to understand whether the action of GA₃ is mediated through IAA: in these varieties. Further in view of the different GA responsiveness of these varieties to oxidative enzymes (KUMAR et al. 1981), plumule growth (KUMAR et al. 1982) and protein metabolism (KUMAR & BAIJAL 1985), GA₃ induced changes in IAA-like substances were investigated for their possible implication in the dwarfism.

Materials and Methods

Sterilized seeds of four wheat varieties viz C-306 (tall), Sonalika (single dwarf), Kalyansona (double dwarf) and Moti (Triple dwarf) were soaked in distilled water with or without GA₃ (1 mg/L) for 24 hours and grown according to the method of KUMAR et al. (1982). Random samples were collected at 0, 48, 96 hours and processed in duplicate for the estimation of auxin-like substances as follows.
Extraction and purification: Weighted samples were ground to a paste and extracted with 80% methanol at 0C for 24 hrs. The supernatent was decanted. Extraction was repeated twice for 5 hrs and 1 hr with fresh methanol. The supernatents were pooled and filtered through a double layer muscline cloth.

The methanol extract was evaporated at room temperature under infra-red light. The aqueous phase was utilized for further extraction and purification of auxins, adopting the technique of NITSCH (1956). The purified acidic and neutral fractions of auxin-like compounds were subjected to chromatography.

Chromatography: The two fractions were concentrated to a few drops and loaded on a Watman No. 1 filter paper strip (40 x 5 cm) and run ascendingly to a distance of about 25 cm at 20 + or - 2C using Isopropanol : Ammonia : water (10:1:1) as solvent. The chromatograms were air dried and cut into 10 equal parts each representing 0.1 RF and as such utilized for bioassy of auxin like substances.

Bioassay: Estimation of auxin activity were carried out adopting wheat coleoptile straight growth test as described by MER et al. (1962). Sections of coleoptile stumps were grown in sucrosephosphate buffer (pH 4.5) with or without the elute of chromatogram. The percent increase (+) or decrease (-) in the length of section with elute over that without it were expressed as promotors and inhibitors, respectively.