Cell protective substances - the fifth line of defense...

Cell protective substances - the fifth line of defense

Plant Cell Protection System

A plant cell is a system of bubbles - compartments covered with membranes. Larger vesicles - nuclei, mitochondria and chloroplasts - are covered with double membranes and contain DNA, t.p. can synthesize their own proteins. Most other vesicles - vacuole, lysosomes, neroxisomes and others - are covered with single membranes. The cytoplasm and various compartments contain chemicals that do not come into contact with each other due to membrane barriers. But if there are damages and ruptures of membranes, the enzymes stored in lysosomes and their substrates, for example in vacuoles, begin to interact, resulting in the formation of new chemicals that are absent in the living cell and many of which are toxic both to the cell itself, and for parasites in it. For example, everyone knows that the root horseradish has a specific smell, but does not cause unpleasant sensations until it is started to rub on the grater. This procedure will cause a flow of tears, coughing, runny nose, since the volatile compounds - isorodanides - resulting from the destruction of membranes with the general formula

R - N = C = S

(where R is a radical, N is nitrogen, C is carbon, S is sulfur) affect the mucous membranes, being tear poisons. In a living cell, they are linked through a sulfur atom to glucose and are called or by thioglycosides. Thioglycosides are present in all plants from the family of cruciferous and are the cause of a specific cabbage-rooted odor, cabbage their concentration is low, and in horseradish and radish - high. Thioglycosides are in vacuoles and are not toxic, but when cells are destroyed, they interact with an enzyme that breaks the bond between glucose and the remaining aglycon that has volatility and high toxicity.

Glycosides in organic chemistry are substances in which a radical having a different nature and called is connected through oxygen with carbohydrates - glucose, galactose, etc. Glycosides are found in the cells of almost all plant species, only most of them aglycons are connected with glucose or with another sugar not through a sulfur atom, but through oxygen. As aglycons, phenolic compounds, terpenoids and even cyanogenic substances (forming hydrocyanic acid in the process of decomposition after breaking with sugar) can act. For example, pentacyclic tristeroid glycosides (containing 30 carbon atoms), which are formed in many plants, are called saponins (from lat. sapo - soap), since they form soap-like solutions in water.

Saponins have an acutely toxic effect on all eucaryotic organisms, from fungi to humans, since, when combined with sterols in membranes, they cause the formation of pores in the membranes and the cell's loss of its contents. Such are the heart's lily-of-the-valley glucosides, digitonin digitalis toxin and other plant poisons. In potato the steroidal aglycone of glucanide solanine has a nitrogen atom in its composition, therefore it belongs to the group of plant alkaloids. It is synthesized only in the light and makes leaves and berries of potatoes, as well as lying in the light (greened) tubers, not only bitter, but also poisonous (see Figure 2.2).

Fig. 2.2. Saponin oats avenacin (left) and potassium glyan alkaloid solanine (right)

The strategy to protect against many pathogens is based on the fact that, by destroying the cell membranes, parasites not only kill the cells of the infected plant, but also contribute to the formation of toxic compounds, causing fire on themselves. The toxicity of dead cells, of which covert tissues (scales of onions, tree bark) are composed, is caused by the same processes - with the death of cells, intracellular membranes that separate substrates from enzymes are destroyed, and aglycones toxic to microorganisms accumulate.

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