Enhancement of ethylene biosynthesis and germination by cytokinins and 1‐aminocyclopropane‐l‐carboxylic acid in Striga asiatica seeds

Abstract

Germination of witchweed (Striga asiatica [L.] Kuntze), an important parasitic weed on several poaceous crops, is stimulated by several synthetic and natural compounds. We investigated the role of ethylene biosynthesis and action in cytokinin‐induced germination. Conditioned Striga seeds treated with distilled water, 1‐aminocyclopro‐pane‐1‐carboxylic acid (ACC) or the cytokinins thidiazuron (TDZ), trans zeatin (TZ), benzyladenine (BA) and kinetin (KIN) produced little ethylene. Treatments with cytokinin‐ACC combinations enhanced ethylene production. The relative order of activity of the cytokinins in elicitation of the phytohormone was TDZ > TZ > BA > KIN. Germination in response to distilled water and ACC treatments was negligible. Induction of germination by cytokinins varied from low (0%) to moderate (52%). Seeds treated with cytokinin‐ACC combinations displayed high rates of germination. The observed germination was positively correlated (γ= 0. 8 and 0. 9) with ethylene production. Germination was reduced by silver thiosulphate (STS) and CoCl2, inhibitors of ethylene action and ACC oxidase, respectively. Aminoethoxyvi‐nylglycine (AVG), an ACC‐synthase inhibitor, reduced TDZ‐induced Striga germination. However, the inhibitory effect of AVG was overcome by addition of ACC. The results are consistent with a model in which Striga germination and embryo growth are limited by low capacity of the seeds to oxidize ACC. The cytokinins promote ACC conversion into ethylene and consequent Striga germination by enhancing ACC oxidase activity and/or synthesis.

Effect of Salinity and Plant Growth Regulators on Seed Germination of Medicago sativa L.

“…Salinity affected adversely the germination of Medicago sativa and adverse effect salinity was reduced by application of hormones. There findings are in close agreement with previous studies on M. sativa and Trifoliurn brachycalycinum and lettuce seed germination under salt stress and its alleviation of additive effects of hormones (Braun and Khan, 1976;Aparacio et al, 1981;Khan and Huang, 1988;Khan and Rizvi, 1994;Khan and Ungar, 1997), Kinetin and other hormones may alleviate stress by enhancing ethylene production by ACC oxidase actively and/or synthesis (Khan and Huang, 1988;Igbinnosa and Okonkwo, 1992;Babiker et al, 1993). However, salinity stress seldom acts alone and its effects on gemination may be modified by interaction with other environmental parameters (Scorer et al, 1985;Khan and Rizvi, 1994).…”

“…Kinetin and GA 3 have also been reported to stimulate seed germination of various species via enhancement of endogenous ethylene production. (Babiker et al, 1993;Igbinnosa and Okonkwo, 1992), However, in present studies GA 3 , and kinetin promoted germination slightly which may be similar to those species which did not respond to kinetin and GA 3 (Saini et al, 1986, Lalonde andSaini, 1992;Zarnstorff et al, 1994). Additive effect of hormone on seed germination has been reported (Sinska, 1989;Tao et al, 1974).…”

The viviparous8 mutation delays vegetative phase change and accelerates the rate of seedling growth in maize

“…Interestingly, amp1 has been shown to increase the endogenous concentration of cytokinin (Chaudhury et aL, 1993). Because cytokinins have been shown to promote germination in several species (Babiker et aL, 1993;Kovac et aL, 1993;Long et aL, 1981;Morris, 1978;Taylorson and Hendricks, 1977), this observation raises the possibility that vp8 mutants may have defects in cytokinin regulation. However, it is important to emphasize that these mutations are not phenotypically identical.…”

The interaction between strigolactones and other plant hormones in the regulation of plant development

“…Still, seed dormancy release depends on an additional reduction of ABA levels which was recently shown to be mediated through ABA catabolism which is triggered by GR24 application (Lechat et al, 2012). Other hormones such as CK and ET can promote parasitic plant seeds germination in the absence of SLs (Logan and Stewart, 1991; Babiker et al, 1993, 1994; Sugimoto et al, 2003), suggesting that they may act downstream of SLs; whereas CK promotes germination by enhancing ET biosynthesis (Babiker et al, 1993). Furthermore, GA is necessary but not sufficient to trigger Striga seeds germination (Toh et al, 2012).…”