Boron deprivation induced inhibition of root elongation is provoked by oxidative damage, root injuries and changes in cell wall structure

Boron (B) is one of the essential micronutrients for the growth and development of higher plants and its deprivation inhibits root elongation. However, little is known about the mechanisms underlying inhibition of root elongation under B deficiency. The present study was carried out with three B levels (0, 5 and 10 μM B) to investigate the effect of B deprivation on the growth of trifoliate orange seedlings and to explore the possible mechanisms involved in the B deprivation induced root growth inhibition. The results indicated that B deprivation severely hampered primary and lateral root elongation with visible symptoms of leaf chlorosis. The B deprivation led to the accumulation of reactive oxygen species, membrane peroxidation and root cell injuries. Boron deprivation not only exhibited reduced concentrations of glutathione but also inhibited the activities of major antioxidant enzymes. Moreover, an elevated accumulation of Ca2+ ion and altered subcellular cell wall structure and disorganized homogalacturonan epitopes were observed in B deficient plants. Taken together, it is concluded that B deprivation leads to root cell injuries, changes in the cell wall structure and accumulates oxidative damage that could be possible causes of root growth inhibition of trifoliate orange under B deprivation.