Other Plant Growth Regulators

When the American Chemical Society was founded in 1876, no more than half a dozen weed-killers were in use (43). In 1936, 60 years later, that number still remained almost unchanged. There now are over 200 herbicides and other plant growth regulators in common use, but the world requirements for food, fiber, and forest products—the principal beneficiaries of herbicides—never were greater. Still, the public is saying clearly that it must know what happens to all these chemicals and what some of the consequences will be. 

Brassinosteroids are active at extremely low concentration, generally 0.1-0.001 ppm solution, which is one hundred time lower range than for other plant growth regulators. 

In most cases, a detectable induction of mRNA levels is observed within 15-30 min following auxin exposure. The levels of three soybean mRNAs (detected by the cDNA clones 6, lOA and 15) are induced by 2.5 min of treatment of excised elongating soybean hypocotyl sections with the synthetic auxin 2,4-D [8]. These mRNAs and others identified in soybean [5, 16], pea [13] and tobacco [14] are specifically induced by auxins such as lAA and NAA, and not induced by nonauxin analogs. With some exceptions, these auxin-induced sequences do not accumulate in response to other plant growth regulators such as GA, ABA, cytokinins and ethylene, or to environmental stresses such as heat shock or cold... 

Until other gibbereUins (- 80) can be either fermented or synthesized in bulk, their future is uncertain for use as industrial plant growth regulators except in very special circumstances. 

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). 

Before leaving the subject of polarity and in relation to uptake and distribution, mention should be made of weak acids and bases. The complicating factor here is that they exist in solution in different forms, the balance between which is dependent on pH. The different forms have different polarities, and thus different values. In other words, the values measured are pH-dependent. Take, for example, the plant growth regulator herbicide 2,4-D. This is often formulated as the sodium or potassium salt, which has high water solubility. When dissolved in water, however, the following equilibrium is established ... 

Trinexapac-ethyl is a plant growth regulator used to prevent lodging in cereals and oilseed rape. Other uses... 

Tables VIII and IX show responses of hydrilla explants to various plant growth regulators and to solstitialin. GA3, BA and solstitialin enhanced elongation at 10-4 or 10 5 M. Zeatin, on the other hand, dramatically increased new shoot initiation in apical explants but had little effect on 2-node explants.

Other products represent only a small share of the crop protection market with plant growth regulators being the largest of this sector and other product types including rodenticides, molluscicides, avicides and nematicides. 

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