Reactive oxygen species and antioxidant enzymes participate in the formation of aerenchyma in barley root under hypoxia

Molecular oxygen is an important factor in plant life. Its deficiency leads to hypoxia, which can occur with excessive moisture of the underground parts of plants. In response to hypoxia, many plants form lysigenous aerenchyma, which performs the functions of oxygen supply. The mechanisms of aerenchyma formation are not entirely clear. Our work describes the anatomical, morphological, physiological and biochemical changes in roots of barley (Hordeum vulgare L.) during the formation of aerenchyma under hypoxia in hydroponic conditions. Oxygen deficiency inhibited root growth and reduced the intensity of respiration rate in them, but did not affect the development of the aboveground organs. Under hypoxic conditions aerenchyma in roots was formed on the 8th day, which was associated with the 2.6-fold increase in the amount of H2O2 compared to the control. The low activity of antioxidant enzymes led to the high H2O2 level. By the 28th day under hypoxic conditions, the activity of benzidine, guaiacol and ascorbate peroxidases increased, which led to a decrease in the H2O2 concentration. We suppose, that the increase of H2O2 concentration in roots triggered the formation of aerenchyma at the early stages of their growth (day 8). Later, antioxidant enzymes utilized reactive oxygen species, ensuring the survival of the roots under hypoxic conditions.