Einfluß exogen veränderter „source-sink”︁-Beziehungen auf die Anzahl der Endospermzellen und die Kornentwicklung bei Sommerweizen

Influence of an exogenously changed source-sink relationship on the number of endosperm cells and grain development in spring wheat In 2 years pot experiments with spring wheat the source-sink ratio was changed by shading the plants at different times after anthesis, by removal of flag leaf blades, and by phytohormone treatment of the ear. The effect of the different treatments was recorded by determining the number of endosperm cells per grain, the single grain weight and the grain yield. In grains of normally illuminated plants the maximum number of endosperm cells was reached 2 to 3 weeks after anthesis. The storage of assimilates within these cells depends on the intensity of illumination during the entire grain filling period. Shading the plants between anthesis and maturity led to a 23 to 34% decrease in grain yield, but only to a 7 to 16% decrease in the number of endosperm cells. The same drop in the endosperm cell number was observed in plants shaded for only 15 days from the start of anthesis. A subsequent period of normal illumination till maturity led to a marked increase in the single grain weight. No decrease in the endosperm cell number was seen in plants shaded from the 15^th day after anthesis till maturity. There was, however, a 12–13% reduction in the single grain weight and grain yield in these plants as compared with the control. Removal of the flag leaf at anthesis reduced the number of endosperm cells by 6 to 11%, the single grain weight by 10 to 29% and the grain yield by 15 to 25%. CCC and Ancymidol treated plants in the shading trials showed the same decrease in the endosperm cell number but a more pronounced reduction in the single grain weight compared with control plants. Their reactions to the various shading trials followed the same general pattern as the control plants. The results of the shading experiments confirm that the endosperm cell number is not the only determinating factor for the single grain weight. The application of kinetin and abscisic acid to the ear had no effect on the number of endosperm cells and single grain weight. Abscisic acid, however, reduced the number of graines per ear.