Comparative effects of allelochemical and water stress in roots of Lycopersicon esculentum Mill. (Solanaceae)

In the present study we compared the effects of allelochemical and water stress on roots of Lycopersicon esculentum. We evaluated the effects on root growth, morphology, H+-ATPase activity, and oxidative damage, to gain an understanding of the modes of action of allelochemicals from the noxious weed Sicyos deppei. Allelochemical stress was produced by 0.5% aqueous leachate of S. deppei and water stress by 12% PEG. Both stresses inhibited root growth by 75% and 76%. Scanning electron microscopy showed that all stressed roots exhibit a lateral swelling in the meristematic zone, but that only allelochemical stress caused an increase in root hairs development. Plasma membrane H+-ATPase activity was reduced by both stresses, allelochemical (50%) and water stress (56%). Water stress caused a higher reduction (42%) in tonoplast H+-ATPase activity than allelochemical stress (28%). Catalase activity was increased 137% by allelochemical stress, and only 47% by water stress. Levels of free radicals increased 44% (allelochemicals), and 32% (water stress), but levels of H2O2 decreased in both (27% by allelochemical, and 52% by water stress). However, water stress caused the highest lipid peroxidation (105%) compared to allelochemical stress (47%). Allelochemical modes of action are discussed.