The uptake of potassium rises. The consequences are an increased uptake of water, a bigger osmotic pressure, damage of the membrane, and finally the disintegration of the cell. Reactions of the Plant Cells on the Activities of the Fungi Plant cells produce a wide range of secondary plant substances, and many of them prevent the growth of fungi. Phytoalexines are lipophilic substances, whose chemical structure poses them among the secondary plant substances. The phytoalexines of the Solanaceae and the Malvaceae are usually sequestiterpenes , that of the Leguminosae are isoflavonoids or polyacetylenes, and the phytoalexines of orchids are dihydrophenanthrenes.
Some plant species like the potato produce several similar substances at the same time.
Little is known about their mode of action. Some results point at an effect that changes the membrane properties of the fungus cell. Other substances seem to block the oxidative phosphorylation, and still others can link up DNA molecules. Phytoalexines provide no absolute protection against fungus infections. They are mainly directed at non-pathogenic species.