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Cellular Defence Mechanisms in Plants

Production of toxic compounds Tannins: these acidic compounds are common in leaves (e.g. tea plant), unripe fruit (e.g. unripe plum), seed coats (e.g. broad beans) and tree bark. They protect against pathogens by acting as enzyme inhibitors.

Cyanide: Hydrogen cyanide is a poison which acts by blocking an organism’s cytochrome system. Toxic cyanide is made in plants from non-toxic glycoside: Enzyme Glycoside Cyanide (non-toxic) (toxic)

Not all plants are able to make glycoside and the enzyme as the ability is determined genetically. A plant which possesses both of the genes is known as cyanogenic (Plants unable to make cyanide are called acyanogenic)

Nicotine: is a toxic chemical produced by the root cells of the tobacco plant and transported to its leaves. Since it is poisonous it protects the leaves from attack by herbivourous insects. Nicotine can be extracted from tobacco plants and sprayed as an insecticide.

Phytoalexins: These are antifungal toxins made by plants in response to enzymes secreted by a fungal hypha.

Top Tip & Handy Hint Three Nasty Chemicals = Tannin Nicotine Cyanide

Isolation / barrier protection Insect galls: When a parasite such as an insect successfully penetrates the tissues of a host plant, the plant often produces a gall in response to chemical stimuli from the parasite. A gall is an abnormal swelling of plant tissue to due rapid cell division which serves to isolate the parasite. They are often filled with tannins which play a further protective role.

Resin: Resin is a sticky substance produced by many shrubs and trees, especially conifers which have many resin canals. Resin is produced in response to parasitic attack and flows into the affected area causing local blockage and isolation of the parasite

Higher Biology Slides 11