Germination stimulants

The germination stimulants are active at extremely low concentrations 0.02 p.p.m. (19) and 0.001 p.p.m. (165). Sunderland (131) reported that the Orobanche minor stimulant from linseed promoted germination at concentrations of 10-8 or 10-9 M. 

The product (4) is a synthetic germination stimulant for parasitic plants. Normally these plants germinate only when the host is growing. Premature germination induced by (4) increases yields of sorghum (an African food crop) planted later. 

Matusova, R. et ah, The strigolactone germination stimulants of the plant-parasitic Striga and Orobanche spp. are derived from the carotenoid pathway, Plant Physiol. 139, 920, 2005. 

The compound (I) was given the trivial name strigol and it has been shown to be a very potent witchweed seed germination stimulant. 

Strigol (I), Isolated from cotton root exudates, Is a very effective germination stimulant for wltchweed [e.g. Strlga aslatlca (L.) Kuntze] seed (1). Structure I depicts the relative... 

Strigol is a natural product with unusually strong properties as a germination stimulant for parasitic weeds of the genera Striga (witchweed) and Orobanche (broomrape). 

The germination stimulant or stimulants from host plants have not yet been identified, but research on isolation and identification of these allelopathic compounds continues. Other nonhost plants, such as cotton, also release chemicals which stimulate the germination of witchweed seed and these crops can replace the cereal crops in witchweed-infected fields. If no acceptable host is present, the witchweed plant is unable to mature and produce seed. The importance of cereal crops as a staple food in underdeveloped countries makes growth of nonhost crops only partially acceptable, and there are numerous wild hosts that allow the witchweed to germinate, mature, and produce more seed (several thousand seeds can be produced by a single plant). Nevertheless, application of either natural or synthetic stimulants in the absence of a host plant is an effective way of reducing and eventually eliminating the witchweed problem. 

Many authors note that test conditions have a strong influence on results, and activity varies widely with a variation in concentration of the germination stimulant. A relatively high concentration of a stimulant often causes inhibition of germination. Preconditioning the seed in the presence of a germination stimulant can also cause inhibition of germination. 

Chang M, Netzly DH, Butler LG, LynnDG (1986) Chemical regulation of distance Characterization of the first natural host germination stimulant for Striga asiatica. J Am Chem Soc 108 7858-7860... 

A similar approach had been described for the synthesis of the mycotoxin patulin (2,3-pyranose-fused unsaturated lactone) from a 2-arabinopyranos-2-uloside derivative,16 and more recently, for the synthesis of a potent germination stimulant and some analogous compounds from D-xylose or commercially available D-glucuronic acid y-lactone.17... 

Pheromones are classified in at least ten different categories. The most conq)lex category involves enantiomers at a specific composition (Mori 2000), implying multiple receptors. Other complex networks of biological events involve terpenoids released by plants in response to grazing by herbivores. These metabolites can be used to attract parasitic wasps for pest control (Tumlinson 1993), or, like the strigolactones (Table 12.1), as useful germination stimulants of root parasites of plants in the families Scrophulariaceae and Orobanchaceae (Welzel 1999 Ryan 2001). 

Welzel, P. R6hrig, S. Milkova, Z. (1999) Strigol-type germination stimulants. Chem. Commun., 2017-8. 

Galindo, J.C.G., de Luque, A.P., Jorrin, J., Macias, F.A. SAR studies of sesquiterpene lactones as Orobanche cumana seed germination stimulants. J Agric Food Chem 2002 50 1911-1917. 

Reizelman, A. Zwanenburg, B. Synthesis of the germination stimulants ( )-orobanchol and ( )-strigol via an allylic rearrangement. Synthesis 2000, 1952-1955. 

The first germination stimulant isolated from a natural host was the hydroquinone SXSg (8), precursor of sorgoleone (9) (Fig. 6.3). This hydroquinone is exuded as oily droplets from the root hairs of Sorghum bicolor and readily oxidizes to the most stable quinone form (9).5 The quinone sorgoleone is a highly... 

Hauck, C., Muller, S., and Schildknecht, H. 1992. A germination stimulant for parasitic flowering plats from Sorghum bicolor, a genuine host plant. J. Plant Physiol. 139, 474-478... 

Hsiao, A. I., Warshem, A. D., and Moreland, D. E. 1988. Effect of chemicals often regarded as germination stimulants on seed conditioning and germination of witchweed (Striga asiatica). Ann. Bot. 62, 17-24... 

Johnson, A. W., Roseberry, G., and Parker, C. 1976. A novel approach to Striga and Orobanche control using synthetic germination stimulants. Weed Res. 16, 223-227... 

Matsui, J., Bando, M., Kido, M., Takeuchi, Y., and Mori, K. 1999. Plant Bioregulators, 3. Synthetic disproof of the structure proposed for Alectrol, the germination stimulant from Vigna unguiculata. Eur. J. Org. Chem. 9, 2195-2199... 

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