Plant growth coumarins

Tannins and lignins are also derived from these pathways but are not included in Table 1. To make the list as simple as possible, all compounds of aromatic nature, viz., simple phenols, benzoic and cinnamic acid derivates, coumarins, flavonoids and quinones are condensed into one group - aromatic compounds. Thus I will attempt to cover systematically the secondary plant growth substances that fall into 11 major groups as shown in Table 1. 

Curry leaf has been reported to contain plant growth inhibitors. Bhattacharya et al. (1989) described the isolation and characterization of two coumarins present in M. koenigii bark. The growth-inhibitory properties are comparable to those of other coumarins, such as psoralen and xanthotoxin. 

The mode of the germination-stimulatory action of coumarin on plant cells has been widely studied [106—110], and it is similar to the action of plant hormones which control different functions and processes of growth. The relationship between the effects of coumarins and auxins has been suggested [106, 107]. Coumarin in different concentrations stimulates stem and shoot elongation [108, 109] it also elicits a similar action [111] on substances which affect root initiation, cambial activity, and leaf expansion [108, 110]. The plant hormones and coumarin also stimulate the growth of roots. In low concentrations, coumarin exerts a synergistic action with plant growth substances, while with... 

This section will review some of the more notable advances of the past few years in elucidating the biological action of coumarins in two areas photobinding to DNA and plant growth regulation. 

Lactones. Physiologically active lactones such as parasorbic acid, coumarin, scopoletin, and protoanemonin occur in many plant families (Figure 2). The lactones may perform a regulatory function in the plant, and have been shown to inhibit germination and to repress root growth [reviewed in detail by Hemberg 61), Evenari 36,37), and Borner 12)]. 

Coumarin, the lactone of o-hydroxycinnamic acid, and some of its derivatives have been isolated from many plant species 31). Thimann and Bonner 141) attributed the growth-inhibiting effects of coumarin to its action on enzyme sulfhydryl groups. Inhibitory effects of coumarin on Avena coleoptiles and pea stem sections could be overcome by 2,3-dimercaptopropanol (BAL). Coumarin has also been reported to disrupt mitosis 29,30). 

Chelidonic acid has been found to exist in the free state in many plants (122). A concentration as high as 10 2 M, calculated on a fresh-weight basis, has been measured. Leopold et al. (89) found that chelidonic acid functioned as a growth inhibitor in the pea straight-growth test. Some inhibition was obtained at 10 5 M and 50% inhibition was measured at 10 4 M. Growth was promoted in the presence of IAA. This action is similar to that noted for coumarin and other unsaturated lactones. As with lactones, the inhibitory effect of chelidonic acid could be relieved by pretreatment of the tissue with BAL. 

Scopoletin is purported as the most widely distributed coumarin in higher plants, and scopoletin, umbelliferone, and esculetin are the ones most frequently linked to allelopathy. Given their phenylpropane origin, it is not surprising that these simple coumarins have many actions in common with the cinnamic acids. One variance is that coumarin and scopoletin have been reported to decrease mitosis,2 whereas at least at concentrations that correlate with growth inhibition, the phenolic acids do not appear to affect cell division. 

Coumarins and their glucosides are ubiquitous and widely distributed secondary metabolites in the plant kingdom. Among them, scopoletin (54), umbelliferone (55), and esculetin (56) are representative allelochemicals. They exhibit various biological activities. In general, these compounds inhibit growth of plants but some display growth promotion at lower concentrations.36... 

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