Role of Ethylene in the Germination of the Hemiparasite Striga hermonthica

Abstract

Seed germination of the hemiparasitic angiosperm Striga hermonthica (Del.) Benth is elicited by compounds present in the root exudates of the host plant. Although a variety of compounds can substitute for the host-derived signal, the mechanism through which these act is unknown. In the present study, an inhibitor of ethylene biosynthesis, aminoethoxyvinyl glycine, was (2,7,12,13,19). In this study we examine the hypothesis that ethylene is the germination stimulant for Striga seeds and that host derived germination signals trigger germination by eliciting the biosynthesis of ethylene. MATERIALS AND METHODS Plant Materials, Growth Conditions, and ChemicalsSeeds of Striga hermonthica (Del.) Benth were collected from Wad Medani, Sudan, in 1989. Seeds were surfacesterilized by washing in a 5% v/v solution of sodium hypochlorite (10-14% w/v available chlorine). Conditioning of seed took place on two sterile circles of Whatman No. 1 filter paper, saturated with sterile double-distilled deionized water, in 9 cm perspex Petri dishes incubated at 33°C in the dark for 7 d. Unconditioned seeds were treated as above except incubation was for 24 h only. Throughout the conditioning period the filter papers were saturated with sterile double distilled deionised water. For host root exudate collection, seeds of Sorghum bicolor (L.) Moench cv CSH-1 were surface-sterilized as above and germinated on moist sterile Whatman No. 1 filter paper at 33°C, after 48 h the germinated seeds were placed on nylon grids suspended over 500 cm3 plastic beakers containing a 20% Long Ashton solution (11), so that the radicles were immersed in the solution. Plants were grown in a controlled environment (day temperature 35°C, night temperature 20°C, 16-h day length, light intensity at bench level of 103 Wm2). Four days later, three plants were transferred to 50 cm3 of sterile double-distilled deionized water and incubated at 20 to 25°C in the dark for 24 h; this solution was used as germination stimulant. All chemicals were of analytical grade or higher. AVG4 and ACC were purchased from Sigma while NDE was purchased from Aldrich.

GR24, a Synthetic Analog of Strigolactones, Stimulates the Mitosis and Growth of the Arbuscular Mycorrhizal FungusGigaspora roseaby Boosting Its Energy Metabolism

“…Thus, in seeds (as in climacteric fruits), ethylene enhances mitochondrial metabolism (Navet et al, 2003). These arguments support the hypothesis of Logan and Stewart (1991) who proposed that germination stimulants of seeds of Striga spp. and Orobanche spp.…”

“…seeds in the absence of the host plant (Parker, 1991). In addition, root exudates of the host plant, as well as strigol and GR24 have been shown to be able to trigger ethylene biosynthesis in Striga seeds (Logan andStewart, 1991, Babiker et al, 1993;Sugimoto et al, 2003). More generally ethylene is known to stimulate seed germination of plants ( Abeles and Lonski, 1969).…”

“…and Orobanche spp., the isolation of strigolactone receptors has remained elusive and their subcellular location is still unknown despite several structure-activity studies . In Striga hermonthica it was proposed that strigolactones act as elicitors of ethylene biosynthesis, leading to subsequent seed germination (Logan and Stewart, 1991). In AM fungi, strigolactones were shown to induce changes in shape, density, and motility of mitochondria after 1 h of treatment (Besserer et al, 2006).…”

Ethylene Controls Adventitious Root Initiation Sites in Arabidopsis Hypocotyls Independently of Strigolactones

“…Furthermore, it has been shown that strigolactone increased production of ethylene in Striga hermonthica seeds while blocking ethylene production, together with strigolactone treatment resulted in no germination of the Striga seeds (Logan and Stewart 1991;Sugimoto and others 2003). These findings support the hypothesis that strigolactone induces ethylene production which in turn affects root hair lengths and germination of parasitic weed seeds.…”

Nitrogen relations of the sorghum‐Striga hermonthica host‐parasite association: germination, attachment and early growth

“…This stage of development therefore represents a distinct point at which control methods may be targeted. However, despite recent advances in our understanding of the mode of action of germination stimulants (Jackson & Parker, 1991;Logan & Stewart, 1991), this approach has been of little use to date, with the notable exception of the use of ethylene in the USA (Eplee, 1992).…”