STUDIES ON SUBMICROSCOPIC ASPECTS OF MINERAL DEFICIENCIES. I. CALCIUM DEFICIENCY IN THE SHOOT APEX OF BARLEY

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Abstract
Marinos, Nicos G. (Waite Agric. Res. Inst., Adelaide, S.A., Australia.) Studies on submicroscopic aspects of mineral deficiencies. I. Calcium deficiency in the shoot apex of barley. Amer Jour. Bot. 49(8): 834–841. Illus. 1962.—The apical dome of the shoot apex of barley, or other cereals, is suitable for the study of submicroscopic cytological changes induced by specific mineral deficiencies because of the many uniform cells available. Also, the well‐defined stages of development of the entire apex make possible, in certain cases, the correlation between growth responses and changes in cell structure. The ultrastructure of shoot apex meristematic cells, after KMnO4 fixation, is fundamentally similar to that of root meristems. The effects of Ca deficiency on cell ultrastructure appear rather suddenly and it has not been possible to reveal unequivocably the initial sequence of events. The first indisputable signs of structural abnormalities appear when the nuclear envelope and the plasma and vacuolar membranes break up and “structureless areas” appear in the cells, followed by the disorganization of other structures like mitochondria and Golgi apparatus, while plastids are more persistent although eventually they also disintegrate. With the progress of Ca deficiency, the cell walls stain darker and gaps may appear, indicating a weakening of their structure. This evidence suggests that Ca is essential for the maintenance and probably for the formation of cell‐membrane systems on which the functional integrity of cell metabolism is dependent; Ca effects on cell walls are probably secondary to those changes already described.