Abscission zone

Oxidimetbiin acts as a defoHant by eliciting the formation of an abscission layer at the middle lameUa, and examination with cotton explants indicates that ceUulase activity is increased at the abscission zone. 

McManus, M.T. Osborne, D.J. (1990). Identification of polypeptides specific to rachis abscission zone cells of Sambucus nigra. Physiologia Plant. 79,471-478. 

The preharvest drop of citrus fruit can be reduced or prevented with 2,4-dichlorophenoxyacetic acid, which delays development in the abscission zone of the fruit stem, thus allowing the fruit to remain on the tree longer. Because of 2,4-D s herbicidal properties, however, care must be taken in spraying to prevent the chemical from damaging other crops, as well as the target crop... 

Anatomy of the abscission zone at the base of mature fruits has been investigated in apples (10), cherries (11), citrus (12), and olives (13) and has been discussed as related to mechanical fruit removal (2, 14), The histochemistry of the separation layer of mature fruit is very similar to that of leaves of citrus (15) and bean (16,17), The actual separation occurs through one or more processes in the separation zone (a) a weakening of the cementing ability of the middle lamella between cells, and (b) a softening of the entire cells (17), In some plants, the abscission zone is structurally differentiated as a layer of compact cells or as a zone of localized cell division in other species, abscission may occur across a transect of cells which show little or no visible diflFerentiation (18). Thus, major components of the separation process involve the dissolution of middle lamella and lysis of cell walls or entire cells in the separation zone, but this is not necessarily associated with distinctive morphological characteristics (19). 

Secondly, in many fruits there are two abscission zones, one between the ovary and pedicel and the other at the pedicel-peduncle (rachis)... 

Ethylene also increases polygalacturonase activity in abscission zones, and this may also contribute to the abscission of some organs 31, 32). The polygalacturonases isolated from plants, however, have been the exo-types 31), and there have been some questions concerning separation of cellulases from polygalacturonase on the basis of a salting procedure (33). 

Cells of the abscission zone of a monocotyledon fruit, the oil palm Elaeis guineensis have been studied by solid state CPMAS NMR. ... 

Explants of Calamondin clearly showed a marked retardation of leaf and fruit abortion (6). Repeated application of brassinolide to intact plants of Calamondin failed to prevent either leaf or fruit abortion (private communication from Dr. Iwahori of Kagoshima University). This suggests that brassinosteroids hardly move into plant abscission zones. Thus, it would be necessary for practical use to find tissues to which brassinosteroids are easily translocated. In contrast it would be almost impossible to use brassinosteroids on young cereal ears to prevent fruit abortion, because they are covered with leaf sheaths. 

Fig. 8. S ed of Ctftntbit. At xtrome right, a seed still hooded by its bract is shown. (X6). At extreme left h the seed of a wild plant, and in the center, of a domesticated plant (both X9K Note that the wild seed is smaller, has an attenuated base, an obvious abscission zone at the base, and is covered with a marbled pepery material (perianth (Reprinted from Small, P/snt Sc/ence BuUbtin, vol. 35, 1975.1...

The earliest attempts to address the question of ethylene receptors did not in fact relate to the latter in the classical sense. In 1975, Beyer [3] showed that higher plants could metabolise ethylene, albeit at very low rates rates so low that a role for this mechanism in controlling ethylene concentration within the plant seemed improbable. However, it became clear that in a number of unrelated systems (cotton abscission zones [4], carnation flowers [5] morning glory flowers [6]) that rates of metabolism correlated with sensitivity... 

At anthesis, the sepals and petals are fully expanded. The petals are no longer postgenitally connected. Nectaries are situated between the androecium and gynoecium, where they form five depressions in the petal radii (Fig 8.2E). After anthesis, the sepals are persistent. The petals and stamens fall off. The long style dries up distally, but also persists for some time and no abscission zone can be seen at anthesis. 

Hu AS, Jiang BF, Guan YL, Mou H (1990) Effects of epi-brassinolide on abscissirai of young fruit explants and cellulose activity in abscission zone citrus. Plant Physiol Commun 5 24-26... 

Effects on Ethylene. Direct desiccation of detached leaves causes a rapid increase in ethylene production. Since the response is larger in leaves with an abscission zone, this stress-induced ethylene production may be related to stress-induced abscission (Aharoni 1977). 

Hall SM, Medlow GC (1974) Identification of lAA in phloem and root pressure saps of Ricinus communis L. by mass spectrometry. Planta 119 257-261 Halliday MBW, Wangermann E (1972 a) Leaf abscission in Coleus. I. Abscission zone formation and the effect of auxin on abscission. New Phytol 71 649-663 Halliday MBW, Wangermann E (1972b) Leaf abscission in Coleus. II. The distribution and fate of [ " C]-indolylacetic acid in the petiole. New Phytol 71 665-670 Hare RC (1964) Indoleacetic acid oxidase. Bot Rev 30 129-165... 

Jacobs WP, McCready CC, Osborne DJ (1966) Transport of the auxin 2,4-dichlorophen-oxyacetic acid through abscission zones, pulvini, and petioles of Phaseolus vulgaris. Plant Physiol 41 725-730... 

Rasmussen HP, Bukovac MJ (1966) Naphthaleneacetic acid localization in the abscission zone of the bean. Science 152 217-218... 

Extracts from citrus orange Citrus sinensis) pedicles contained cellulase activity. The effects of pH, ionic strength, and ethylene on the extraction of cellulase from the abscission zones of citrus-leaf Citrus sinensis) explants have been studied. Prior treatment of the explants with ethylene increased the solubility of the enzyme in phosphate buffers, regardless of pH,... 

Writtenbach VA, Bukavac MJ (1975) Cherry fruit abscission peroxidase activity in the abscission zone in relation to separation. J Amer Soc Hort Sci 100 387-391... 

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