What is abcission layer in plants



Abscission refers to the shedding of leaves, fruits and other parts of plants such as leaf and flower buds, twigs, spines, thorns or inflorescences. One therefore speaks of leaf fall, fruit fall, leaf fall, bud fall, flower fall.

Abscission can be associated with self-cleaning for the plant by removing old, injured or diseased parts. Furthermore, an excretory function is possible in which organs in which metabolic waste products have accumulated are rejected. It also plays a role in the spread of fruits and asexual reproductive bodies.

The shedding of the plant parts is preceded by characteristic morphological and anatomical changes in the separation zones. There is often a pronounced separating fabric. This is located at the base of the leaf or fruit stalk and consists of particularly small parenchymal cells with dense protoplasm. Here the separation process is prepared in that the middle lamellae and / or primary walls or whole cells dissolve in a two to three cell layer wide separation layer, which differs from plant species to plant species. For this correlatively controlled active process, atmospheric oxygen and a respiratory substrate are required. Respiratory toxins inhibit abscission. Ribonucleic acid and protein synthesis are also necessary, especially the synthesis of cellulase and pectinase.

Pectinase, which makes protopectin water-soluble, is actively secreted from the protoplasm into the cell wall. Auxin, senescence factors and ethylene including abscisic acid are involved in the correlative control of abscission.

Auxin, which is formed in intact, not yet aged leaves and fruits and migrates through the petiole, prevents abscission. Accordingly, in horticultural practice, premature fruit fall is often suppressed by spraying the plants with auxin solutions. On the other hand, they stimulate senescence factors that migrate from aging leaves and flowers. With many fruits and some leaves, e.g. B. the lupine, there is a temporal correlation between abscisic acid production and abscission. According to the senescence hypothesis of abscission, the willingness of the separating tissue to abscission is regulated by the ratio of auxin to senescence factors.

Factors that delay leaf and fruit senescence, e.g. B. cytokinins, delay the abscission accordingly. Ethylene is the direct regulator that induces it when the separating tissue is ready to abscission, among other things through the formation of ribonucleic acid, cellulase and / or pectinase. Differential gene activation is considered to be the primary effect of this ethylene effect. In addition, ethylene inhibits auxin synthesis and transport, so it stimulates abscission in two ways. Ethylene-releasing preparations are often used to accelerate or synchronize fruit ripening. This is important for the mechanization of the harvesting processes.

The withering autumn leaves is an allegory for the necessity that renewal causes the negation of the traditional: the trees have to shed their leaves in order to be able to sprout fresh, new leaves in the next spring.

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Category: Plant Development