TENTATIVE DETERMINATION OF THE MOLECULAR-WEIGHT OF SUBSTANCES STIMULATING THE FLOWERING OF WINTER-WHEAT

Murashige & Skoog nutrient was supplemented with substances of molecul ar weight (Mw) less than 5 kDa, which were separated from extract of w inter wheat ears by means of Sephadex G-25 ultrafiltration. Isolated e mbryos of the same wheat cultivar (Grana) were vernalized in the nutri ent for 0 and 7 days at 2 degrees C for 2 weeks and planted in a glass -house. After 150 days of growth (20/17 degrees C day/night) the devel opment of the shoot apices was observed. It was found that substances of Mw<5 kDa strongly stimulated the generative development of the plan ts, enabling the caring of 30 % of non-vernalized plants (control = 0 %) and 100 % plants vernalized for 7 days (control = 29 %). The substa nces present in the extract of both spring (cv. Jam) and winter (cv. G rana) varieties were fractionated by means of Sephadex chromatography into 300 fractions of Mw = 1 to 5 kDa and each of them was added to th e isolated embryos of cv. Grana. The embryos were vernalized at 2 degr ees C for 7 days and then cultured as previously described. It was fou nd that the differentiation of the shoot apices was stimulated by over 34 % by fractions of winter wheat extract and more than 50 % by fract ions of the spring wheat extract. However, only a few of identical fra ctions of the extracts of both wheat varieties were able to induce the earing of the plants. These fractions were grouped in 4 continuous in tervals of Mw equal to about 4.5-4.9, 3.2-5.3, 2.1-2.6 and 1.00-1.03 k Da. Within the three intervals was identified a small group of identic al fractions, which affected the growth of the seedlings in similar mo de i.e. inhibiting or stimulating. Thus it can be assumed that these i ntervals contained identical or similar substances capable of stimulat ing strongly the earing of winter wheat.