Controlling abscission

A major factor leading to abscission is the weakening of the middle lamella, cell walls, or cells in a separation zone across the petiole, pedicel, or stem. Although any of the known plant hormones can alter the progress of abscission, ethylene remains unique as the principal stimulus of the increased activity of wall-degrading enzymes in abscission, whereas auxin can be given a central role in the retardation of abscission. With the present level of understanding, it would seem that abscission control involves interactions between auxin and ethylene. 

The measured dose ratios are then used to calculate Log (DR-1) ordinates for the corresponding abscissal logarithm of the antagonist concentration that produced the shift in the control curve. A linear equation of the form... 

The phenomenon of leaf and fruit drop is known as abscission and has been suspected for some time to be under hormonal control. Dr. Addicott s description of the structure and properties of Abscisin II, the abscission hormone isolated from cotton, climaxes over 12 years of his own investigations on the subject and represents perhaps the greatest advance in plant hormone research in the past decade. It also provides an unusual and unsuspected structural model to guide... 

Abscisic acid, as the name suggests, has been implicated in the control of abscission of leaves, flowers and fruits, as well as with the function of stomata in response to water stress (Figure 5.4). Abscission involves the synthesis of cellulase in the ageing process and it is thought that abscisic acid influences the rate at which this proceeds. 

Fig. 1. Ethylene biosynthesis. The numbered enzymes are (1) methionine adenosyltransferase, (2) ACC (l-aminocyclopropane-l-carboxylic acid) synthase, (3) ethylene forming enzyme (EFE), (4) 5 -methylthio-adenosine nucleosidase, (5) 5 -methylthioribose kinase. Regulation of the synthesis of ACC synthase and EFE are important steps in the control of ethylene production. ACC synthase requires pyridoxal phosphate and is inhibited by aminoethoxy vinyl glycine EFE requires 02 and is inhibited under anaerobic conditions. Synthesis of both ACC synthase and EFE is stimulated during ripening, senescence, abscission, following mechanical wounding, and treatment with auxins.

Control of stem-end rots caused by A. citri, D. natalensis, and P. citri with postharvest applications of the growth regu-lators 2, 4-D and, occasionally, 2,4,5-T is attributed to preservation of the green button and prevention of abscission (106,... 

Henry, W. H., "Control of abscission in agricultural crops and its physiological basis", Plant Physiol. (1968)... 

Plate 6. Effects of SOj on red current brushes (Ribes rubrum L.) in the second year of exposure to fumes of an iron smelter. Sparse foJiage, small leaf size premature leaf abscission and little or no fruit could be seen at a distance of 600 m from the source (left). The damaging effects were less expressed at a distance of 750 m. Healthy looking brushes could be observed at the control site situated 6000 m from the source. Biersdorf, W. Germany. 1960 (right). Photograph by courtesy of H. van Haut. 

Touring the past two decades intensive research has been conducted on the phenomenon of organ abscission in plants. A basic knowledge of the processes gives insight into the metabolism of cell walls which has applicability in attempts to control the ripening process in many fruit production programs. 

Attention in this review is directed toward abscission of mature fruits. Since plants abscise organs naturally, we examine the nature of the abscission process from the standpoint of structural changes and enzymes involved how plants seemingly regulate a selective control over abscission natural and synthetic chemicals affecting abscission whether... 

A recent development in the field of chemical abscission formulations has been the use of mixtures of chemicals to induce and to control fruit loosening. CHI and Release have been shown to have a synergistic influence on fruit abscission (108). 

Use Fungicide, antibiotic, abscission of citrus fruit in harvesting, turf disease control. 

Phytohormones are those compounds that regulate and control the physiological phenomena of higher plants such as growth, maturation, abscission and dormancy. They are biosynthesized at a special part of a plant, then migrate to the places where they control the various physiological phenomena. Seven major phytohormones are shown in Figure 2.1. 

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