The antagonistic effects of kinetin and spermine on stress imposed by seawater on leaf area,
pigment, Hill reaction, 14CO2 fixation and chloroplast ultrastructure of wheat flag leaf were
investigated. Irrigation of wheat plants by seawater at 25% caused marked decrease in leaf
area, pigment content, Hill activity and photosynthetic efficiency of wheat flag leaf at ear
emergence. Grain priming with kinetin, spermine or their interaction alleviated the adverse
effect of seawater stress by stimulating leaf area expansion, pigment production as well as
photosynthetic activity. From transmission electron microscopy micrographs, a continuous
“end-to-end” distribution of regular (oval or elliptical) chloroplasts around the cell’s periphery
was observed in flag leaf mesophyll cells of control wheat plants. Conversely for
seawater-stressed plants, the irregular spherical chloroplasts appeared “bulbous” and
discrete, the cells also displayed extensive but thin peripheral cytoplasmic regions devoid of
chloroplasts. Grain presoaking in 0.1 mM kinetin caused the chloroplast of stressed wheat
plants to be more regular, with organized membrane system, large starch grains and projections
in the form of tails. Furthermore, ultrastructure analysis cleared that grain priming
with spermine, either alone or incombination with kinetin, caused the chloroplast in flag leaf
mesophyll cells of stressed wheat plants to be more regular in shape with more starch grains.
The changes in pigment content and photosynthetic activity of flag leaf appeared to depend
mainly on chloroplast ultrastructure and its numbers, showing a positive correlation between
chloroplasts number and pigment content.