THE EFFECTS OF SALT STRESS ON THE SHOOT APICAL MERISTEM AND LEAF GENIERATION IN SUNFLOWER (HELIANTNUS ANNUUS L.)

Sunflower (Helictnthur annuus L. cvs Mehr Shafagh) seedlings were grown in nutrient solutions containing 20.5 to 70.4 mM NaCl and 0 as the control. The effects of salinity on developmental changes occurring in the shoot apices of plants were studied. At 20.5 mM NaCI concentration, the leaf emergence rate and plastochron index of Shafagh increased significantly, but this phenomenon was not observed in Mehr. These parameters decreased in 41 mM and higher salt concentrations. In Shafagh plants, anatomical changes in shoot apical meristem at 20.5 mM NaC1 consisted of the meristem and increased density and chromophilly in rneristem cells, which are indicators of stimulated mitosis, pitrticularly in the peripheral zone. No changes were observed in Mehr. In both cultivars, 41 mM and greater NaCl concentrations led to an increase in the width of meristems, uniform chromophilly of cells and dispersed mitotic activity. These phenomena are assumed to be signs of the transformation of a vegetative apical meristem into a reproductive one. The leaf segments shortened and xylem differentiation was seen nearer to the apex. The shoot apical meristem of Shafagh cultivar plants at 20.5 mM NaCl appeared to be activated for leaf generation. The effect of high salt concentrations on precocious flower formation of sunflower is also discussed