Cellular ultrastructure and net photosynthesis of apple seedlings under iron stress

Abstract

Iron deficiency was induced in apple seedlings (Malus domestica Borkh.) grown in solution culture. Severity of leaf chlorosis increased when seedlings were grown in nutrient solutions containing 0.13 ppm Fe at pH 6.5; no Fe at pH 5.5; no Fe at pH 6.5, and no Fe at pH 7.8. Seedlings grown in solutions containing 1.3 ppm Fe at pH 5.5 remained green. Iron deficiency reduced the amount of protoplasm present in the cells. Iron sufficient cells developed normal chloroplasts, containing numerous large starch granules. Leaf net photo synthetic (Pn) rate was 11.6 ug CO₂/hr/dm². Iron deficient plants grown in pH 5.5 solution developed abnormal chloroplasts with dispersed grana and osmosphilic bodies. The size and number of starch granules were reduced and leaf Pn rate was 3.7 mg CO₂/hr/dm². As the pH of the nutrient solution increased the degree of organization of the chloroplasts and the Pn rate decreased. No starch was found in chloroplasts from plants receiving no Fe and growing at pH 6.5 or 7.8. Iron deficiency at high pH usually has been assigned to both decreased Fe solubility and decreased uptake. In this experiment Fe deficiency has been shown to be aggrevated by increasing the nutrient solution pH even though Fe was not taken up.

Key words:

• chloroplast
• solution pH
• iron deficiency
• root Fe
• leaf Fe

Notes

Visiting Research Horticulturalist, Institute of Pomology, Chinese Academy of Agricultural Science, Beijing, Peoples Republic of China.

Supervisory Plant Physiologist, Plant Stress Laboratory, Agricultural Research Center, U. S. Department of Agriculture, Beltsville, MD.