Morpho-physiological and ultrastructural changes of Arabidopsis seedlings treated with phloretin

Abstract

Phloretin is a phenolic compound unique for apple (Malus × domestica Borkh.) species. Our research group recently reported phytotoxic potential of phloretin towards other plant species such as model plant Arabidopsis. Since sugars in in vitro growth media could modulate plant metabolism, we analyzed phloretin effects on Arabidopsis seedlings grown on the medium with out sucrose and myoinositol (WSM) but enriched with different concentrations of phloretin (0 to 1500 µM). Phloretin treatment on WSM induced seedlings growth retardation at much lower concentrations compared to sucrose and myoinositol enriched medium. Inhibition of primary root and leaf growth, and lateral root emergence increased with both phloretin concentration and treatment duration (maximal 85.2%, 30.4% and 46.5% at 1500 µM phloretin at 15 days after germination - DAG, respectively). Prolonged cultivation (4 weeks) at phloretin concentrations over 500 µM induced complete growth stagnation and necrosis of the leaves. Transmission electron microscopy reviled relocation of chloroplasts within mesophyll cells, shape change into spherical form, as well as ultrastructural changes in thylakoid organization in leaves of 10 DAG-old seedlings treated with 250 or 500 µM phloretin. Significantly decreased number of starch grains in chloro plasts and chlorophyll a and b content in leaves reflected impaired function of chloroplasts due to ultrastructural changes. Phloretin also induced cell wall undulation and folds that resulted in irregularly shaped mesophyll cells. The presented study revealed that beside roots that had been previously emphasized as primary targets of phloretin action, leaves were also significantly affect ed by phloretin treatment, especially in the aspect of photosynthetic apparatus