Relationship of Boron Nutrition to Radiosensitivity of Sunflower Plants.

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Abstract
Seven-day-old Mammoth Russian sunflower seedlings (Hellanthus annuus) were grown in nutrient solutions with or without B, for 2 to 5 days, after which they were X-irradiated and again supplied with B. Withholding B for short intervals prior to X-irradiation with doses that normally produce pronounced radiation symptoms, had a marked alleviating effect on the development of radiation injury. The absence of B resulted in retardation of some phase of cellular activity and rendered the plants more radioresistant. This normally radiosensitive phase of cellular activity which may be rendered relatively radioresistant by withholding B is, then B-dependent. A series of germinating seedlings were irradiated at different growth stages, to identify this growth phase. It appeared to be the phase of cellular maturation rather than cell division. Experiments in which applications of Cl4 sugar were made to leaves of B-deficient and B-sufficient plants with or without excised terminal buds indicated that the apparent effect of B on sugar translocation is related to the effect of B on cellular activity rather than to a direct enhancement of diffusion through membrane through formation of a sugar-borate complex.