The Role of Boron in Plant Growth

Estimates of cell number, cell volume, respiratory rate, nitrogen, sugar, and nucleic acid content were made on 1 mm. sections of the radicles of field bean at frequent intervals during the first 96 hours of growth in nutrient solutions with and without boron. The primary effects of deficiency were cessation of cell division and enlargement of the apical cells. The increased volume of the apical cells may have been due to either a longer period being available for development as the rate of mitosis decreased, or to an unusually rapid rate of cell extension. The results indicated that cell division did not cease for lack of available sugar nor as a result of failure to synthesize protein or nucleic acids. It is suggested that in the absence of boron division ceases because abnormalities in the formation of the cell wall prevent the cell from becoming organized for mitosis. In particular the hypothesis that boron is concerned with the formation of ‘pectin’ from uridinediphosphate-D-glucose is examined in the light of published evidence.