Anatomical responses of root tips to boron deficiency

Abstract

Abstract Ultrastructural changes induced in young tomato root tip cells by the absence of boron from the nutrient solution were investigated with an electron microscope. Detailed observations of cortical cells revealed lome ultrastructural effects of boron deficiency as follows: 1) Lack of boron disordered the shape and arrangement of cortical cells. The abnormal accumulation of a “lipid-like substance” was observed. 2) In boron-deficient root tips, cell walls suffered an irregular thickening followed by a rugged or serrated structure. Occasionally, the disorganization of middle lamellae occurred and an accumulation of numerous vesicles was observed in the disorganized area. These cell wall alterations appeared most distinctly in the longitudinal walls. 3) Baron deficiency also caused an abnormal development of the Golgi apparatus. The number and size of secretory vesicles particularly increased in boron-deticient root tip cells. This abnormal development of the Golgi apparatus seemed to be related with the irregular thickening of cell walls. 4) The effect of boron deficiency on cell walls and on the Golgi apparatus appeared primarily in the cells in the extension region and extended into the merilltematic region as boron deficiency advanced. 5) The irreversible damage on root elongation in the advanced stage of boron deficiency was not associated with any necrotlc symptom at sub-cellular level such as a degradation of the membranous system or a decrease in the integrity of the ground substance.