abscission

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Abscission

The process whereby a plant sheds one of its parts. Leaves, flowers, seeds, and fruits are parts commonly abscised. Almost any plant part, from very small buds and bracts to branches several inches in diameter, may be abscised by some species. However, other species, including many annual plants, may show little abscission, especially of leaves.

Abscission may be of value to the plant in several ways. It can be a process of self-pruning, removing injured, diseased, or senescent parts. It permits the dispersal of seeds and other reproductive structures. It facilitates the recycling of mineral nutrients to the soil. It functions to maintain homeostasis in the plant, keeping in balance leaves and roots, and vegetative and reproductive parts.

In most plants the process of abscission is restricted to an abscission zone at the base of an organ (see illustration); here separation is brought about by the disintegration of the walls of a special layer of cells, the separation layer. The portion of the abscission zone which remains on the plant commonly develops into a corky protective layer that becomes continuous with the cork of the stem.

Diagrams of the abscission zone of a leafenlarge picture
Diagrams of the abscission zone of a leaf

Auxin applied experimentally to the distal (organ) side of an abscission zone retards abscission, while auxin applied to the proximal (stem) side accelerates abscission. The gibberellins are growth hormones which influence abscission. When applied to young fruits or to leaves, they tend to promote growth, delay maturation, and thereby indirectly prevent or delay abscission. Abscisic acid has the ability to promote abscission and senescence and to retard growth. Small amounts of ethylene have profound effects on the growth of plants and can distort and reduce growth and promote senescence and abscission.

abscission

[ab′sizh·ən]
(botany)
A physiological process promoted by abscisic acid whereby plants shed a part, such as a leaf, flower, seed, or fruit.
References in periodicals archive ?
1), suggesting that water stress and stress relief had minimal effects on starch levels in abscised leaf tissue at the end of seed filling.
- We collected all of the stigmas from focal plants after the corollas abscised. Collecting stigmas at this stage has no effect on pollen tube germination or fruit set (Waser and Fugate 1986).
Considering only fruits with filled seeds, larvae were present in 65.7% of the abscised fruits and 26.9% of the fruits still on trees.
In this case, the biomass of the leaves was not considered, as an infestation of spider mites (Family: Tetranychidae) destroyed some of the leaves, and other leaves had senesced and abscised by the end of the experiment.
Abscised peaches were collected at Byron, GA, in 2004 and placed on trays with mesh bottoms over a large aluminum funnel (0.3 m high with a slope of 30%).
After water-stress sampling, plants were rehydrated and allowed to recover for 1 wk, at which time each plant was mapped and the number and location of bolls, squares, incompletely abscised fruit, and aborted positions were recorded.
To estimate floral lifespan, flowers of Houstonia serpyllifolia were tagged as they opened and followed until the corolla abscised. Floral lifespan was followed in the greenhouse in December 1990 and in a natural population at Whiteside Mountain, near Highlands, in June 1991.
Damaged and infested lanterns are often abscised by the plant and heavily infested plants usually have a large number of lanterns on the ground.
Application of the latter equation (using height of the canopy surface as the source height) is likely to severely underestimate pollen deposition near a source; canopy obstacles do play a role in local pollen deposition on the forest floor, and pollen released in clusters (Andersen, 1970; Tonsor, 1985; DiGiovanni et al., 1995) or retained in abscised flowers or microstrobili will not travel far from the source.
(Only one leaf is produced per node.) The dry mass of abscised leaves was added to the dry mass of the stems.
For example, insect mines or galls are more likely to be abscised in young cottonwood or willow tissue than are more mature tissue, resulting in induced resistance (Williams and Whitham 1986, Preszler and Price 1993).