High NaHCO3 stress causes direct injury to Nicotiana tabacum roots

In order to localize the main organic site of alkaline toxicity to plants, the injury of NaCl or NaHCO3 to tobacco (Nicotiana tabacum L.) seedlings was compared. The results showed that the injury effect of alkaline stress on tobacco were much stronger than salt stress, with respect to growth retardation, photosynthetic inhibition, and ionic unbalance. The root/shoot ratio, transpiration rate, and Na+ accumulation in the leaves were lower than other. Further investigation of the root ultrastructure showed that the endoplasmic reticulum and nuclear membrane were not visible or absent, while more small vacuoles and mitochondria with dilated or absent cristae were observed under the 100 mM NaHCO3 stress. These results indicate that under alkaline conditions, the endomembrane system of root cells is directly and seriously damaged. This possibly causes the failure of water absorption and ion compartmentalization.