Effect of boron on cell elongation and division in squash roots.

This work establishes that cessation of root elongation of intact squash (Cucurbita pepo L.) plants is an early result of boron deficiency. Root elongation is slowed by 6 hours and is virtually stopped as early as 24 hours after boron is first withheld from the nutrient solution. As root elongation ceased, cell elongation progressed distally into the region normally occupied by the apical meristem and eventually the meristem became indistinguishable. Differentiation was determined by use of an elongation index in which cell length was compared to cell width. This index ranged from a low of 0.8 in boron-sufficient root meristems to a high of 3 in root meristems grown in a boron-deficient nutrient solution for 98 hours. It is concluded that a continuous supply of boron is not essential for cell elongation but is required for maintenance of meristematic activity. Boron may act as a regulator of cell division in this tissue.