Sensitivity of chickpea and faba bean to root-zone hypoxia, elevated ethylene, and carbon dioxide

During soil waterlogging, plants experience O-2 deficits, elevated ethylene, and high CO2 in the root-zone. The effects on chickpea (Cicer arietinum L.) and faba bean (Vicia faba L.) of ethylene (2 mu L L-1), CO2 (2-20% v/v) or deoxygenated stagnant solution were evaluated. Ethylene and high CO2 reduced root growth of both species, but O-2 deficiency had the most damaging effect and especially so for chickpea. Chickpea suffered root tip death when in deoxygenated stagnant solution. High CO2 inhibited root respiration and reduced growth, whereas sugars accumulated in root tips, of both species. Gas-filled porosity of the basal portion of the primary root of faba bean (23%, v/v) was greater than for chickpea (10%), and internal O-2 movement was more prominent in faba bean when in an O-2-free medium. Ethylene treatment increased the porosity of roots. The damaging effects of low O-2, such as death of root tips, resulted in poor recovery of root growth upon reaeration. In conclusion, ethylene and high CO2 partially inhibited root extension in both species, but low O-2 in deoxygenated stagnant solution had the most damaging effect, even causing death of root tips in chickpea, which was more sensitive to the low O-2 condition than faba bean.