Absorption of Polyethylene Glycols by Plants and Their Effects on Plant Growth

S ummary A study was made of polyethylene glycols (PEG) as osmotica to decrease the water potential of culture solutions for studies of higher plant response to water stress. Analysis of possible inorganic impurities in commercial PEG and comparison of the growth of maize in solutions purified by gel filtration or unpurified, suggest that impurities are not responsible for the toxic effects reported. PEG in leaves was estimated by Hyden's method and with 14 C‐labelled PEG 4000. Over 90 % of the higher molecular weight PEG was recovered from maize and bean leaves but less from cotton and tulip tree. PEG of 1000 molecular weight or larger entered plants slowly, about 1 mg/g fresh weight of leaf per week, but mechanically damaged roots or those subjected to low water potentials permitted entry. PEG decreased transpiration and water potential and caused the leaves to die. PEG 200 and mannitol entered plants with undamaged roots but the effects on leaves were unlike the higher molecular weight PEGs. Low and high molecular weight PEG and mannitol affected respiration to the same extent and comparison with non‐ionic detergents showed that the detergent properties of PEG were not responsible for the toxicity. Autoradiography showed that PEG 4000 accumulated initially in the margins of leaves and became distributed in the mesophyll except along the veins. PEG of higher molecular weight is considered to cause blockage of the pathway of water movement, reducing water absorption and causing desiccation of the plant.