The electron microprobe X-ray analyzer (microprobe) has been used to determine the mode of entry of aluminum (Al) and its distribution and localization in the corn plant. Microprobe analysis is a non-destructive method allowing for multiple element analysis in the same tissues, cells or cell organelles.Al was found to be precipitated on the surface of the epidermal cells of the root with no penetration into the cortex as long as the root surface remained intact. The root cap was freely permeable and contained the highest concentration of Al. The epidermal layer behind the root cap prevented movement into the cortex and conductive tissue.The penetration of a lateral root through the endodermis, cortex and epidermis provided a channel of entry for Al into the cortex and conducting tissues of both the lateral and main root. Essentially no Al was found in the transition zone and only small quantities were present in the above-ground plant parts.The localization of phosphorus was exactly the same as that of Al. This suggested that there was a precipitation of P by Al. A similar analysis for calcium and phosphorus on control plants did not reveal such a precipitation.The method of sample preparation was critical in retaining and localizing the elements in question and is discussed in that light.

Abscission layer formation in the sour cherry (Prunus cerasus L.) during fruit maturation occurred in the transition zone between the fruit and the pedicel. The abscission layer, consisting of 5-8 rows of cells, was first identified by its low affinity for haematoxylin. The walls of cells in the abscission layer contained less total polysaccharides than adjacent cells. The pectins were degraded and the cellulose was partially broken down resulting in cell separation. The Ca level in the abscission zone decreased and Ca and Mg were lost from the walls of cells in the layer during abscission. After the abscission layer formed, cells associated with the layer had a lower capacity to bind (45)Ca than cells distal or proximal to the layer.

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The halophyte Salicornia pacifica var. utahensis grows in the desert saline playa. The fused leaves form succulent stems and have apparently isolated tracheids in the palisade region as observed by scanning electron microscopy. Frozen shoots were fractured under liquid nitrogen and scanned for Na+, K+, and Cl− with an electron microprobe X-ray analyzer. In young shoots, the palisade cells were low in salts, and the spongy cells had higher concentrations. The salt in the spongy cells provides a high osmotic pressure permitting the plant to absorb more water from the soil. As the shoots matured, the concentration of salts increased in the spongy cells, and the amount of salt in the palisades also increased. The salt ions in the palisades were excluded from the organelles and were mainly present in the vacuoles. Eventually, the leaf section collapsed because of the high salt in the palisade and spongy cells, but the vascular region in the shriveled section continued to function. The sections adjacent to the dead shriveled section remained green and succulent. The salt tolerance appeared to be based on the exclusion of the salt from the photosynthetic cells and on the ability of the succulent stem to function even though sections were dead owing to high salt concentration.