Induced Abscission Sites in Internodal Explants of Impatiens sultani: A New System for Studying Positional Control

Methyl jasmonate induces the formation of secondary abscission zone in stem of Bryophyllum calycinum Salisb

“…In addition, it was reported that the differentiation of abscission zones in abnormal positions on stems, petioles or branches can occur in vivo in response to tissue injury or infection. When stem, petiole or pedicels are excised from the whole plant, certain parts of them will also form secondary abscission zones in vitro (Addicott 1982, Pierik 1977, 1980, Warren Wilson et al 1986, Warren Wilson et al 1987. The important regulators to induce abscission zone were shown to be auxin and ethylene (Osborne •989).…”

Bean leaf abscission: Tissue-specific accumulation of a cellulase mRNA

“…It has been 'assumed that these cells are cryptically differentiated and preprogrammed to respond to the abscission signal (Osborne 1989;McManus and Osborne 1990). Although in most abscission layers, including bean, the cells that will be involved in the normal, natural abscission process are assumed to be genetically determined prior to the onset of abscission (Osborne et al 1985), adventitious abscission zones can be induced by exogenous hormone treatments (Addicott et al 1955;Wilson et al 1986;Osborne and McManus 1986;Osborne 1989). Osborne (1989) described an auxin and ethylene treatment which induced adventitious abscission in the petioles of bean that exhibited enzyme-production, cellenlargement, and cell-separation responses that were similar to those of normal abscission zones.…”

“…Osborne (1989) described an auxin and ethylene treatment which induced adventitious abscission in the petioles of bean that exhibited enzyme-production, cellenlargement, and cell-separation responses that were similar to those of normal abscission zones. Addicott et al (1955) and more recently Wilson et al (1986) and Osborne (1989) proposed that the formation of an auxin gradient regulated the position of adventitious abscission. Although the mechanism for abscission-cell differentiation in bean is unclear, it is informative that expression of cellulase genes in abscission is not limited to a particular cell type but instead is positionally-specific, involving many cell classes.…”

Shoot-tip abscission and adventitious abscission of internodes in mulberry (Morus alba)

“…In the short laterals, photoperiod is not an important determinant of shoot-tip abscission (Fig, 1), resulting primarily from the dominance of the upper, long sboots and intense competition among laterals along the stem (Suzuki andKobno 1987, Suzuki 1990a;cf, also Leakey and Longman 1986), The imposition of dominance and abscission are both delayed by enhancement of shoot growth in 1-year-oid saplings (rooted cuttings) potted in a light clay soii and supplied witb spring nitrogen fertilizer (Suzuki and Kitano 1990), suggesting that nitrogen availability may be important in shoot growth and shoot-tip abscission in mulberry (cf, also Millington 1963), Abscission is highly likely to be associated with stem ageing (senescence) because excision of the node of tbe last vigorous leaf during and after shoot-tip abortion and abscission had only a little effect on the adventitious abscission of the distal intemode (Tab, 1; cf, also Warren Wilson et al, 1986Wilson et al, , 1987b, After apex abscission of the short shoots, the termitial btids are predormant (summer) to dormant (autumn) unless tbe upper, long shoots are removed (Suzuki andKobno 1987, Stizuki 1990b), After release of bud dormancy in the following spring, they can grow out again. However, the growth of most short sboots is very limited; they often bear flower buds with no developing leaf, or only one or more leaves and therefore lose branch vigour a year or more after the first year of growth, they then die and are shed by natural pruning (as defined by Kramer and Koziowsiii 1979), Decapitation-induced, adventitious abscission of the distal internode of the upper, long sboots (Tabs 2 and 3, Fig.…”

“…Abscission normally occurs at certain well-defined sites, for instance, at the base of petioles and in fruit stalks, where a transverse separation layer, often only two or three cells thick, differentiates by degeneration of the middle lamellae (Addicott 1982, Sexton andWoolhouse 1984), Very little is known about the processes that define the position of separation layers with such precision, although the subsequent activation of separation layers has been much studied and characterized. Recently, with stem explants of Impatiens sultani, Warren Wilson et al, (1986Wilson et al, ( , 1987aWilson et al, ( ,b, 1988 developed a hypothesis about the positional control mechanism, suggesting that separation layers tend to arise when auxin concentration decreases in the apical direction.…”