Abscission

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. 

Naphthalene Acetic Acid and Naphthalene Acetamide. Naphthalene acetic acid [26445-01-2] (38) is historicaHy one of the first plant growth regulators. Reports concerning its activity in crops and plants have been a subject in much of the eady Hterature (57). Consequently, it has been used as a starting matedal for other compounds, eg, vide infra Sevin. Naphthaleneacetamide [31093-43-3] (39) has been used as a standard matedal to evaluate abscission pnor to 1953 and its effect on apple drop was reported in 1953 (58). The substance is used as an internal standard in the abscission bioassay (59). 

Hydrogen fluoride Tip and margin bums, dwarfing, leaf abscission narrow brown-red band separafes necrotic from Youngest leaves most sensitive Epidermis and mesophyll cells 0.1 (ppb) 0.08 wi. i... 

Bleaching between veins, tip and margin burn, leaf abscission marking often similar to that of ozone... 

Chlorosis and abscission brown spotting yellowing of veins... 

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 location along the abscissal axis for this curve yields the ICS0 for the 50% inhibition of the response ([B] =ICSo)... 

When an experimental value is obtained numerous times, the individual values will symmetrically cluster around the mean value with a scatter that depends on the number of replications made. If a very large number of replications are made (i.e., >2,000), the distribution of the values will take on the form of a Gaussian curve. It is useful to examine some of the features of this curve since it forms the basis of a large portion of the statistical tools used in this chapter. The Gaussian curve for a particular population of N values (denoted x ) will be centered along the abscissal axis on the mean value where the mean (r ) is given by... 

Sigmoid, the characteristic S-shaped curves defined by functions such as the Langmuir isotherm and logistic function (when plotted on a logarithmic abscissal scale). 

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... 

Chemistry and Physiology of Abscisin II, an Abscission-Accelerating Hormone... 

Abscisin II is a plant hormone which accelerates (in interaction with other factors) the abscission of young fruit of cotton. It can accelerate leaf senescence and abscission, inhibit flowering, and induce dormancy. It has no activity as an auxin or a gibberellin but counteracts the action of these hormones. Abscisin II was isolated from the acid fraction of an acetone extract by chromatographic procedures guided by an abscission bioassay. Its structure was determined from elemental analysis, mass spectrum, and infrared, ultraviolet, and nuclear magnetic resonance spectra. Comparisons of these with relevant spectra of isophorone and sorbic acid derivatives confirmed that abscisin II is 3-methyl-5-(1-hydroxy-4-oxo-2, 6, 6-trimethyl-2-cyclohexen-l-yl)-c s, trans-2, 4-pen-tadienoic acid. This carbon skeleton is shown to be unique among the known sesquiterpenes. 

The extraction and purification, leading to the crystallization of abscisin II, were guided by an abscission bioassay (1). Seedlings of... 

Fig. 32. Streamlines in abrupt contraction flow computed at a midtravel distance of the piston at x = — 40 mm (the origin of the abscisse is taken at the orifice entrance). Due to axial symmetry, only half of the flow tube is shown. The dimensionless stream function

Taylor,J.E., Tucker,G.A., Lasslett,Y., Smith,C.J.S., Amold,C.M., Watson,C.F., Schuch,W., Grierson,D and Roberts,J.A (1990) Polygalacturonase expression during leaf abscission of normal and transgenic tomato plants. Planta. 183.133-138. 

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