Abscission

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Abscission referred to in the Herblore shedding of leaves, fruits and other plant parts such as leaves and flower buds, twigs, spines, thorns or inflorescences. It is therefore also called leaf drop, fruit drop, leaf fall, bud drop or flower case. It is an aspect of senescence in plants.

With the abscission can be linked by removing old, damaged or diseased parts of the plant self-cleaning. Furthermore, an excretory function possible by organs are shed in which metabolic waste products are accumulated. Another is the role of abscission in the spread of fruits and asexual reproduction bodies.

The shedding of plant parts is preceded by characteristic morphological and anatomical changes in the separation zones. Frequently creates a distinct separation fabric. This is located at the base of the leaf or fruit stalk and consists of very small parenchyma cells with dense cytoplasm. Here, the separation process is prepared by different in a two to three cell layers wide separation layer of plant species to plant species, dissolve the middle lamella and / or primary walls or whole cells. Atmospheric oxygen and respiratory substrate are required for this correlative controlled active process. Respiratory poisons inhibit abscission. Needed are further ribonucleic acid and protein synthesis, especially the synthesis of cellulase and pectinase.

Pectinase, which makes protopectin water, is actively secreted by the protoplasm in the cell wall. At the correlative control of abscission auxin, Seneszenzfaktoren and ethylene are involved including abscisic acid.

The plant hormone auxin, which is formed in intact, not yet aged leaves and fruits and migrates through the petiole, prevents abscission. Accordingly, in the horticultural practice of premature fruit drop is often suppressed by the plants are sprayed with Auxinlösungen. Seneszenzfaktoren moving from senescent leaves and flowers, they stimulate other hand. With many fruits and some sheets, such as lupine, there is a correlation in time between the Abscisinsäureproduktion and abscission. After Seneszenzhypothese abscission the Abszissionsbereitschaft the separation tissue is regulated by the ratio of auxin to Seneszenzfaktoren.

Factors that delay the leaf and Fruchtseneszenz such as cytokinins delay accordingly abscission. Ethylene is the direct regulator which induces when the separator is in Abszissionsbereitschaft tissue, including through the formation of RNA, cellulase and / or pectinase. Differential gene activation is considered to be the primary effect of ethylene action. In addition, ethylene inhibits auxin synthesis and transport, so it stimulates abscission in two ways. Ethylene -releasing preparations are often used to speed up or synchronization of fruit ripening. This is for the mechanization of harvesting operations of importance.

Deciduous woody plants

Deciduous trees and shrubs shed their leaves in autumn before or during the first frosts or in the dry season ( " leaf fall " ), which reduces the risk of desiccation in winter with frost areas or in the dry season. The coloring concluded as follows: The production of chlorophyll (green ) is set, and other dyes are visible (yellow and orange carotenoids and xanthophylls ). In addition, anthocyanins can be formed, which turn the leaves red.