Growth cessation, plant

The composition of the waters, and the movement, and the growth, and the removal and restitution of bodily nature, and the splitting off of the spirit from the body, and the fixation of the spirit on the body are not operations with natures alien one from the other, but, like the hard bodies of metals and the moist fluids of plants, are One Thing, of One Nature, acting upon itself. And in this system, of one kind but many colours, is preserved a research of all things, multiple and various, subject to lunar influence and measure of time, which regulates the cessation and growth by which the One Nature transforms itself. 

The first symptom after application is the cessation of growth (2-3 days). Then chlorosis begins and the plants die in 2 to 4 weeks depending on climatic conditions. 

There are several ways to alter effective levels of putative hormones. The first is to excise a plant tissue that is incapable of synthesizing the hormone itself, and allow the tissue to become depleted of the hormone. If this causes cessation of a particular response, and upon readdition of the compound the response is restored, there is reason to believe that the compound is a hormone controlling that process. For example, excision of sections of coleoptiles results in a marked decline in growth rate [13]. Since auxin can restore the growth rate, while none of the other hormones can substitute for auxin, the evidence that coleoptile cell elongation is regulated by auxin is strong. 

The failure to chemically define, lAA biosynthesis, has been a source of confusion in research on the auxins. This failure resulted logically from the manner in which auxins were defined, discovered, and studied. Hormones were defined by Starling [7] as organic compounds synthesized in one place, then, transported to a second place where they would exert their effect. This definition is an operational one and the manner of discovery of animal hormones by Berthold [8] and plant hormones, first by Ciesielski [9] and then Darwin [10] served to emphasize this definition. The first studies of plant hormones involved removal of the tip of a plant root or shoot, which resulted in the cessation of growth (see review by Went and Thimann [11]). Replacement of the tip, or placement of... 

Nonetheless unanswered questions remain. What are the relative contributions of branched chain amino acid deficiency and AKB overabundance to the cytotoxic effects of the sulfonylurea and Imldazollnone herbicides Will the delineation of the cytotoxicity of AKB towards typhimurium, the only system in which it has been approached, provide relevant information towards the roles of this molecule in the Inhibition of plant growth Can herbicide-resistant alleles of ALS structural genes be used as dominant selectable markers In the transformation of a wide variety of sensitive cell lines What are the structural details of the interaction of ALS with the sulfonylurea and imldazollnone herbicides Are eukaryotic ALS Isozymes composed of nonldentlcal subunits How does SM cause cessation of DNA synthesis in plants In the next few years answers to some of these questions may emerge. 

Herbicidal sulfonylureas have a unique mode of action they interfere with a key enzyme required for plant cell growth - acetohydroxyacid synthase (AHAS, EC 2.2.1.6) [1, 2, 3] (see also Mark E. Thompson in this volume, Chapter 2.1 Biochemistry of the Target and Resistance ). AHAS is the enzyme responsible for the synthesis of the branched-chain amino acids valine, leucine and isoleucine. Inhibition of this enzyme disrupts the plant s ability to manufacture proteins, and this disruption subsequently leads to the cessation of all cell division and eventual death of the plant. 

The imidazolinone herbicides (Table 2.3.1) are a family of six compounds that were discovered and developed by American Cyanamid Corporation. Readers may obtain comprehensive and detailed information in The Imidazolinone Herbicides [1], a book authored by the researchers who discovered and developed the herbicides. The herbicides as a class are broad spectrum and are active both pre-and postemergence. Imidazolinones are absorbed and moved through both xylem and phloem, eventually accumulating in the meristematic tissue. Activity is characterized by rapid cessation of growth followed by plant death days or weeks after treatment. Selectivity is based most often on metabolic inactivation except for selection-developed target site based resistance. 

Oxyacetamides and tetrazolinones taken up via the soil provide a strong effect on meristem bearing cell division in the root and shoot tips. Complete arrest of cell division results in cessation of growth and distortion of elongated tissue, leading to plant death. 

Inhibition of protein, RNA, and DNA synthesis by herbicides has been the subject of numerous reports and reviews (see, e.g.. Refs. 3, 4, and 137-139). Inhibition of the biosynthesis of any of these macromolecules would lead to an effective and abrupt cessation of plant growth. However, with very few exceptions, the reports on herbicidal interference with protein and nucleic acid synthesis reflect secondary effects resulting from an effect at a target site elsewhere in the cell. For example, any interruption of the production of metabolic energy, as a result of respiratory uncoupling and/or inhibition, would lead to a rapid cessation of macromolecular synthesis. In several surveys of herbicide effects on C-labeled precursor incorporation into protein and RNA in excised plant tissues and isolated mesophyll cells, dinitrophenols and hydroxybenzonitriles were the most potent inhibitors (Section 5.1 see, e.g.. Refs. 138 and 140). 

Kadota, A., Wada, M., and Furuya, M., Apical growth of protonemata in Adiantum capillus-veneris 3. Action spectra for the light effect on dark cessation of apical growth and the intracellular photoreceptive site. Plant ScL Lett., 15, 193, 1979. 

HjS, like SO2, is a gaseous environmental pollutant which is taken up by plants and affects plant growth. Gaseous HjS results in enhanced levels of sulfur in plants, mostly as sulfate but also as thiols, especially cysteine and utathione (de Kok et al.. 1983, 1985 Maas et al., 1985, 1987a,b). Interestingly, the concentration of glutathione decreases after cessation of H2S treatment, suggesting that this product is subsequently metabolized. 

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