The antifungal activity of commercial Thymus vulgaris oils on the development of mycelium of the the phytopathogenic fungi Fusarium solani (Mart.) Sacc., Rhizoctonia solani Kühn and Colletotrichum lindemuthianum (Sacc. et Magn.) Briosi et Cav. was studied. The gas chromatography data showed that the essential oils were rich in thymol (22-38%) and its biogenetic precursors γ-terpinene and p-cymene. The carvacrol content was relatively low in all the oils tested, ranging between 1% and 2%. The fungicidal activity of the oils was correlated with their thymol content.The principal chemical components of thyme oils were then tested using the same concentrations as in the thyme oils. Only the fungicidal activity of thymol was high and close to that of the oils with the same thymol content. The effects of the thyme oils and thymol on the hyphae cytomorphology of the studied fungi was an increased vacuolization of the cytoplasm and accumulation of lipid bodies, undulations of the plasmalemma, and alterations of the mitochondria and endoplasmic reticulum.

The aquatic plant Lemna minor L. was treated with sodium selenite or sodium selenate to test the toxicity of these salts in relation to high or low levels of sulfate in the culture medium. Several morphophysiological aspects, such as multiplication rate (MR), ratio of the number of fronds to number of colonies (Nfr/Ncol), frond size, cell ultrastructure, pigment content and guaiacol peroxidase (EC 1.11.1.7) activity were evaluated. Their variations might be an indirect means of evaluating the degree of susceptibility or tolerance of this plant to selenium (Se). Sodium selenite or sodium selenate treatments at concentrations ranging from 1 to 256 μM generally decreased the investigated parameters. Moreover, the sulfate concentration influenced the toxicity of both Se salts. In general, with treatments in a medium containing a high sulfate (HS) content, sodium selenite appeared more toxic than sodium selenate, whereas in a low sulfate (LS) medium, sodium selenate seemed more toxic. MR was significantly increased at 1–4 μM selenite and LS or 8 μM selenate and HS levels, suggesting that Se may be an essential nutrient for this plant.

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SUMMARY -Morphological, anatomical and ultrastructural differences have been observed in fronds of two months old cultures of Lemna minor L. These fronds are reduced in area and in thickness and never form colonies. They have been compared with normal and ABA treated fronds in order to determine if the above mentioned differences could be caused by ABA, which might have been released in the culture medium.

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