Plant growth bioassays

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). 

The results presented here demonstrate that these approaches can be applied to Potamogeton sp. and Hydrilla verticillata. In both assay systems, typical responses to known plant growth regulators were observed in most cases. The unique response of P.nodosus to ABA however, clearly shows the importance of not relying solely on "classical" bioassays. 

Several authors have obtained circumstantial evidence that allelopathic compounds reduce mycorrhizae formation (20-23). Kovacic and associates ( ) have shown that understory plants in a live ponderosa pine stand are largely nonmycorrhiza-forming species. They hypothesized that this was due to inhibition of the vesicular-arbuscular mycorrhiza necessary for the growth of herbaceous mycorrhizal plants, under living pines. They demonstrated that more mycorrhizal plants occurred under dead pines, bioassay plants formed mycorrhizae in soils beneath dead pines but not in soil beneath live pines, and mycorrhizal inoculum appeared to be absent from the live pine stand. 

Although the bioassay of racemic parasorbic acid showed good activity (wheat seed root growth was 50% inhibited with 0.25 mg/mL), the conclusion that little of the growth-retardant activity in cranberry leaves can be accounted for by parasorbic acid was confirmed by examination of Devlin s extract. In this case neither parasorbic acid nor its glucoside was present. Subsequent work by Hussain (12) has resulted in the isolation of two plant growth inhibitors identified as cinnamyl alcohol and 3-pheny1-1-propanol (hydrocinnamyl alcohol). 

Several lines of evidence support the conclusion that allelopathic inhibition of germination and plant growth typically occurs from the joint action of several allelochemicals. Additive or synergistic effects have been shown in bioassays with combinations of monoterpenes, organic acids, and several classes of phenolic compounds. These experiments demonstrate that a specific compound may be present below its threshold for inhibition and still be active in allelopathic interference by its effect in concert with other allelochemicals. 

The canaline-pyridoxal phosphate complex lacks discernible toxicity as evaluated by the J.. minor bioassay, even at a concentration of 10 M where canaline virtually stops plant growth. 

The studies on the inhibitory effects of podolactones A (29) and E (51) and nagilactone E (36) were extended to a range of bioassays [73]. In some of these assays, the effects of the podolactones were compared to those of lycoricidinol and harringtonolide, plant growth inhibitors (Table... 

Conn, K.L., Nowak, J., Lazarovits, G. A gnotobiotic bioassay for studying interactions between potatoes and plant growth-promoting rhizobacteria. Can J Microbiol 1997 43 801-808. 

One of the metabolites of the trichothecene family of mycotoxins, termed "neosolanoil" (246) was isolated from Florunner peanuts and identified as 3a-hydroxy-4B, 8a-15-triacetoxy-12,13-epoxy trichothec-9-ene. This toxin was shown to be a potent plant growth inhibitor active to 10 % in the wheat coleoptile bioassay. 

In a search for safer biodegradable plant growth substances that may have potential uses in agriculture, particularly for crop production, our laboratory has developed some new bioassay systems to screen various plants for growth-regulating activity. Our screening efforts resulted in the discovery of both growth promoters and inhibitors. 

Since many of the plant growth substances now have been structurally characterized, it is no longer necessary to rely on bioassays for PGS identification. In fact, physico-chemical techniques have become the methods of choice. There have been a number of reviews discussing some of the aspects of PGS analysis by physico-chemical procedures (1, 2, A, 5). This report will... 

Cutler, H. G. 1984. A fresh look at the wheat coleoptile bioassay. Proceedings of the 11th Annual Meeting of the Plant Growth Regulator Society of America, pp. 1-9... 

The first plant bioassay [Avena sativa L (oat) coleoptile test] was employed by F.W. Went in the 1920 s to demonstrate the existence of and to quantitatively assess the first growth-modifying substance [indole-3-acetic acid (IAA)] isolated from plants.122 Plant bioassays have been extremely useful and intimately linked to the discovery and characterization of the major classes of plant hormones. In fact, many of the bioassays used now were developed for PGRs. Bioassays have been used to screen, evaluate phytotoxicity or plant growth promotion, study mode... 

Since the use of techniques to measure IAA, bioassays have been important to discover PGR activity of many other compounds. Several bioassays for the PGR gibberellic acid (GA3) have been developed. One bioassay was based on reduction of amaranthin levels in Amaranthus caudatus (tassel flower) seedlings.63 This method was sensitive to GA3 from 0.01 to 1 mg L"1. GA3 was also bioassayed, based on anthocyanin reduction in tomato (Lycopersicon esculentum L.).62 Reduction of anthocyanin in tomato seedlings was linear from 10"5 to 10 mg L 1, and thus, this latter plant bioassay method was more sensitive. A multitude of bioassays for nonvolatile and volatile plant growth regulator compounds have been developed and their uses and limitations have been discussed.129 Since many allelochemicals have been shown to have relatively weak phytotoxicity (especially compared to herbicides), some of these bioassays that have been developed for detecting and quantitatively measuring PGR activity may be useful in allelopathy. 

Elakovich, S. D. 1995. Bioassay methods applied to allelopathic herbaceous vascular hydrophytes. Proc. Plant Growth Regul. Soc. Amer. pp 39-43... 

Mangnus, E. M., Stommen, P. L. A., and Zwanenburg, B. 1992. A standardized bioassay for evaluation of potential germination stimulants for seeds of parasitic weeds. J. Plant Growth Regul. 11, 91-98... 

Yopp, J. H., Aung, L. H., and Stefens, G. L. 1986. Bioassays and other special techniques for plant hormones and plant growth regulators. Plant Growth Regulat. Soc. Amer. 208 p. 

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