Ribonucleic Acid Content, Boron Deficiency Symptoms, and Elongation of Tomato Root Tips.

Boron is recognize(d as an essential micronutrient for higher plants, but the precise role of this element in plant growth and development is not clear. In Gaugh and Dugger's (3) comprehensive review they presented and discussed a wide spectrum of proposed roles and effects of boron on higher plants. From their own work and their interpretative review of the literature they concluded that "boron may be essential for sugar transport in higher green plants," and "boron deficiency symptoms are an expression of sugar deficiency in the cambia, stem tips, root tips, and flowers and fruits." From reports that have appeared since their review was published in late 1954, it appears that the role of boron in sugar translocation per se must be indirect (5, 8, 9. 13, 17). that sucrose does not readily alleviate the svmptoms of boron deficiency (1, 6, 7, 15), and that as much or more carbohydrate was found in boron-deficient root tips as in boron sufficient tips (5, 16). Although the exact functioni of boron in planit irietabolism is unknown, a common feature on which mlan-y investigators agree is that boron is essential for the normal growth and functioning of apical meristems (1, 7). WVhittington (14) reported that a deficiency of boron caused a cessation of cell divisioln and later suggested (15) that in the absence of boron, cell division ceases because abnormalities in the formation of the cell wall prevent the cell from becoming organized for mitosis. However, Skok (13) concluded from radiosensitivity studies with sunflower plants that boron is required "for some process or processes concerned with cellular maturation or differentiation rather than with cell division." Albert and Wilson (1) found that external symptoms of boron deficiency of roots of intact tomato plants were detected within 24 hours after boron was withheld from the nutrient solution. These svmptoms consisted of the cessation of root elongation as early as 6 hours after boron was withheld and the subsequent development of a brown color and loss of fluorescence in the terminal portion (2mm) of the root tips. Brown root tips did not resume elongation when again supplied with an adequate amount of boron. However, roots that ceased