Germination of Tagetes minuta L. II. Role of gibberellins

Abstract

The effect of the application of gibberellins to Tagetes minuta L. achenes (seeds) was determined at both 25T, the optimal germination temperature, and 35T, at which temperature the achenes are thermoinhibited.Both GA, and GA,+, accelerated germination at 25 "C. Seed germination at 25 T was inhibited by paclobutrazol, but on subsequent application of GA,+, rapid germination was induced. Following application of GA, or G&+, to thermoinhibited seeds, a significantly higher final germination percentage was observed than in the distilled water control. However, endogenous gibberellin levels in germinating and thermoinhibited seeds did not differ significantly.

Comparison of endogenous cytokinins and cytokinin oxidase/dehydrogenase activity in germinating and thermoinhibited Tagetes minuta achenes

“…Removal of the fruit coat and leaching of the achenes prior to imbibition had no effect on the alleviation of thermoinhibition, showing that thermoinhibition in T. minuta is not coat-imposed (Taylor et al, 2005). Exogenous cytokinins had an inhibitory effect on germination of T. minuta (Taylor et al, 2005) while gibberellins had a positive effect and could partially overcome thermoinhibition (Drewes and van Staden, 1990), especially when applied in combination with an ABA biosynthesis inhibitor (fluridone) and ethylene (ethephon; Taylor et al, 2005). These results show that control of thermoinhibition in T. minuta is due to the interaction of a number of endogenous factors, mainly hormonal, that are actively imposed at the embryo level (Taylor et al, 2005).…”

Isolation of cDNA clones for genes that are differentially expressed during thermoinhibition in achenes of Tagetes minuta L.

“…At 25°C in white light, 100% germination was achieved, compared with only 27% in the dark at the same temperature. In the light, germination typically takes between 2 days (Drewes and van Staden 1990;Hills et al 2001) and 7 days (Forsyth and van Staden 1983), depending on the seed lot. The optimum germination temperature appears to be 25°C, with 10 and 35°C representing the lower and upper limits to germination, respectively (Forsyth and van Staden 1983).…”