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