Development, ethylene stimulator

The ripening of nonclimacteric fruits is usually considered as a process that as a whole does not require ethylene. Nevertheless, endogenous ethylene is involved at some steps of development of these fruits. In general, chlorophyll degradation in nonclimacteric fruits is believed to be ethylene stimulated, whereas the synthesis of pigments can depend on ethylene action or not. ... 

Ethylene as a stimulator of growth and development. The most observed actions of ethylene on growing plants involves growth inhibition, or acceleration of senescence. These actions are especially evident in the antagonism or opposition of ethylene to auxins, gibberellins and cytokinins (27), as already outlined above. Actually ethylene stimulates growth in many types of cells, especially in water plants (Table II). When ethylene acts to stimulate cell elongation, as in water plants, auxins and CC>2 enhance the ethylene effect (38,39). This interaction is the reverse of that observed on land plants wherein ethylene opposes the effects of auxin, GA3 and cytokinins. 

Finally, two case studies were presented briefly to give a better feel for what research and development activities are all about. Vinyl chloride monomer production showed how the availability of cheap raw materials (e.g. ethylene) stimulated the development of processes to utilize these, and how continuing research and development led to new, even better processes. It also emphasized the importance of reading the chemical literature. Development and production of CFC replacements demonstrated what an enormous R D effort can achieve in such a short time. Great emphasis on research and development is a key characteristic of high technology industries like the chemical industry. 

Olefin copolymerization and reactor blend formation are important processes to tailor polyolefins. Copolymer properties depend upon the sequence distribution of the comonomers, which is controlled by means of catalyst as well as process technology. Today most copolymers are produced either in solution processes or in solvent-free gas phase polymerization. Recent breakthroughs in catalyst development are stimulating production of a novel range of copolymers, especially of ethylene copolymers. In the past, special catalysts were designed to produce three classes of ethylene copolymers with different comonomer content ... 

None of these compounds has been reported in natural stimulant preparations. Similarly, Riopel 2) in a more recent review noted that many compounds promote or inhibit seed germination. Ethylene is an effective germinator, but its use in under developed countries is minimal. 

The dramatic increase in 6-MM content--90 to 270 fold in two samples--was unexpected. 6-MM is a potent antifungal agent (4) and one of the most important carrot phytoalexins. Usually 6-MM, one of the components that contributes to the bitterness of stored carrots ( O), is not detected in fresh carrots, but develops during storage. Biosynthetic studies indicate that 6-MM is synthesized via the acetate pathway and its production is stimulated by ethylene (. Thus, UV light may trigger ethylene production in carrots which in turn leads to 6-MM accumulation. 

In 1996, Brookhart and co-workers developed a remarkable class of Pd complexes with sterically encumbered diimine ligands (Scheme 4, S4-1, S4-2, S4-4, and S4-5). These examples are capable of mediating the co-polymerization of ethylene with methyl acrylate (MA) to furnish highly branched PE with ester groups on the polymer chain ends by a chain-walking mechanism (Scheme 10). " This represents the first example of transition metal-catalyzed ethylene/MA co-polymerization via an insertion mechanism. The mechanism for co-polymerization is by 2,1-insertion of MA and subsequent chelate-ring expansion, followed by the insertion of ethylene units. The discovery of these diimine Pd catalysts has stimulated a resurgence of activity in the area of late transition metal-based molecular catalysis. Recently, the random incorporation of MA into linear PE by Pd-catalyzed insertion polymeriza-... 

Development of ethylene [64] starts about 40-60 min after mechanical perturbation, much earlier than generation of salicylic acid [53]. This perturbation is induced, for instance, just by wind [30], explaining the observation that the rice blast disease (induced by pathogens) is suppressed in seasons of strong wind (apparently the perturbation induces expression of ethylene, this stimulates generation of phytoalexins which prevent attack by fungi). 

Defoliation. Interest in defoliation has been low in recent years. One relatively new development is the "wiltant which is applied only shortly before harvest (51). As an outgrowth of some basic studies, several auxin transport inhibitors, TIBA, DPX-1840, Alanap (N-l-naph-thylphthalamate), and morphactins (2-chloro-9-hydroxyfluorene-9-car-boxylic acid), were shown to promote ethylene- and ethephon-mediated leaf abscission (52, 53). Subsequently, CA3 was found to be even more active in promotion of ethylene-induced abscission (54). It now appears that the CA3 counteracts the inhibitory effect of auxin on ethylene-induced leaf abscission (55) thus, CA3 might improve the performance of any defoliant that achieves part of its action by stimulating stress-induced ethylene production and lowering the natural auxin content of the dam-... 

Ethylene physiology of the plant can be manipulated in a variety of ways. In the past, the use of ethylene was limited to exposure of plants to the gas in containers thus, fleld applications were impractical. This limitation was removed by the discovery and commercial development of ethephon in which the liquid active ingredient, 2-chloroethyl phos-phonic acid, is converted to ethylene by the plant (59). Other means of modifying ethylene physiology have been recognized and discussed (4, 5). It is possible to stimulate ethylene synthesis with auxins (60, 61, 62, 63), abscisic acid (64), defoliants (65), ascorbic acid (66), cyclohexi-mide (66), and iron salts (66), among other compounds. A number of physical, environmental, microbial, and insect stresses increase ethylene synthesis, including moisture stress (67) and air pollutants (68). 

Brassinosteroids are reported to stimulate overall plant growth and development, especially under stress conditions, to enhance auxin-induced growth as well as auxin-induced ethylene production (5, 6). Brassinosteroids interact with most of the phytohormones, such as cytokinins and gibberellins, and in particular with auxin. 

---