Abscission agents

Abscisic acid (ABA), 13 305 Abscission agent, ascorbic acid as, 25 761 ABS (acrylonitrile-butadiene-styrene) materials, producers and trademarks of, 10 207t. See also ABS polymers ABS resins Acrylonitrile-butadiene-styrene entries ... 

Several materials have commercial use as abscission agents (6). In cotton, the products Accelerate (endothall), Folex (merphos) and DEF (oxidized form of merphos) have been identified as defoliants. Amid-thin continues to be used to thin fruit set. 3-CPA and Peach-thin 322, formerly used as peach thinners, serve as reminders of the disadvantages of highly specialized markets. RELEASE and PIK-OFF are under development as citrus abscission agents. 

Over the past several years, we have included within the scope of agricultural R and D efforts the search for abscission agents with prime emphasis on citrus abscission. My comments in part will be drawn from factors which have effected the development of the potential abscission agent RELEASE by Abbott Laboratories. Examples relative to the general concerns and obstacles in the development of a plant growth regulator will also be discussed. 

Factors Affecting Abscission Agents Such as RELEASE. ... 

With such cooperation, mutual support and obviously some "luck" (23), plant growth regulators, including abscission agents, may still be expected to be developed (24, 25) not only to enhance quality and yields of major crops e.g., cotton, corn, tobacco, but also important fruit crops e.g., apples, oranges (citrus), grapes, cherries, etc. 

To date, use of L-ascorbic acid as an abscission agent on any crop is not carried out on a commercial scale on a regular basis. 

One of the most interesting papers on ascorbic acid-Cu reactions showed that ascorbic acid-Cu catalyzes the formation of ethylene from several precursors. The interest in ethylene was as an abscission agent in plants. All alcohols, aldehydes, acids, ethers, and epoxides formed ethylene when mixed with Cu and ascorbic acid in 5-mL closed bottles at 30 °C for 1 h. Methional was the most active, followed by propanal, propanol, propyl ether, ethyl ether, and ethanol. This reaction may be part of the oxygen scavenging system because Cu increases ascorbic acid s ability to scavenge oxygen. The authors claim this reaction cannot be attributed to copper in its lower valence state. 

Chemical aids to harvest and fruit abscission agents are reviewed and discussed in relation to structure, mode of action, and predictability of response. Also, an attempt is made to assess the physiological basis for different responses among fruits of differing physiological age and among various organs on the same plant. 

Separately, and in combination with ethephon, succinic acid, 2,2 -dimethylhydrazide (SADH), has been tested as an ejffective coloring, and sometimes abscission, agent in cherries 84, 94), peaches (89, 95-99), apricots (99), and apples (93, 100, 101, 102). Combinations such as... 

Chloro-3-methyl-4-nitro-lH-pyrazole (Release) has no auxin-, gib-berellin-, or cytokinin-like activity, yet it is an ejffective abscission agent. At the present, there is no evidence to indicate that Release retards auxin, gibberellin, or cytokinin activity. It does stimulate and enhance the tissue production of ethylene (105). Release is fairly stable, and there is no indication that it is degraded by the tissue to ethylene per se (106). 

Ethylene is produced in measurable amounts in a number of fruits, leaves, and shoots under normal conditions (7, 46, 59, 72) and in large amounts after treatment with certain chemicals 14, 43, 44, 46), mechanical stresses (72), and adverse environmental factors (73). Thus, acceleration of abscission by many agents seems to occur via ethylene production—a fact that is being used to assay chemicals as potential accelerating agents for abscission 74). Apparently, this is the basis for the induction of abscission by placement of abscission chemicals on the surface of an organ such as an orange 41). 

Toxic to aquatic organisms for example, there was an inhibiting effect of 20-40 ppm aniline on the pigmentation of Xenopus laevis embryos, and of a concentration as low as 1 ppm on the body size of the young toads. Investigation of the death of pine trees in the United States found air pollution from aniline as the most likely causal agent for the needle necrosis and needle abscission. 

Use Nutrition, color fixing, flavoring and preservative in meats and other foods, oxidant in bread doughs, abscission of citrus fruit in harvesting, reducing agent in analytical chemistry. The iron, calcium, and sodium salts are available for biochemical research. 

---