Effects of mixed saline and alkaline stress on the morphology and anatomy of Pisum sativum L.: The role of peroxidase and ascorbate oxidase in growth regulation

The effects of hyperalkaline, thermo-mineral water from Slatina on the morphology and anatomy of pea plants (Pisum sativum L.), were examined after eleven days of treatment with a mixture of tap water and Slatina water in 3:1 (T1) and 1:1 ratios (T2). Complete growth arrest of seedlings was observed in the Slatina water (T3). The alkalinity of external media was recovered to pH 8 within four days only in T1 and T2. Analysis of morphological parameters (the length of the main root, root application zone, number of lateral roots) indicated that the thermo-mineral water either promoted (T1) or inhibited (T2) the formation of lateral roots and plant growth. Comparative histological and anatomical analyses showed that inhibition of lateral roots was accompanied by an increase in the xylem and phloem. These changes in root morphology were accompanied by an increase in the activity of superoxide dismutase (SOD: E.C. 1.15.1.1) and peroxidase (POD: E.C 1.1.1.17) in the soluble fraction, whereas the activities of ascorbate oxidase (AAO: E.C. 1.10.3.3) bound to the cell wall and ionic POD decreased. The lower ratio of Slatina water in the hydroponic solution contributed to a more developed mesophyll with significantly higher AAO activity in the leaves and the induction of ionic POD isoforms. Besides alkalinity and excess NaCl, we suggest that a specific combination of metals (e.g. Ca and Mg) might be responsible for subtle changes in the cell area and xylem development, leading to dramatic changes in root anatomy.