Endogenous hormones in afterripening wild oat (Avena fatua) seed

Abstract

TAYLOR. J. S.. a n d G . M. SIMPSON. 1980. Endogenous hormones inafterripening wild oat (Acetin frrttrri) seed. Can. J. Bot. 58: 1016-1024. Levels of gibberellins and cytokinins in dormant Auetirr frrtlrn L. seeds were measured by bioassay during the afterripening process. Little change in the level of either hormone was detected in the dry seed. Following imbibition of fully afterripened seed, however, gibberellin levels increased while cytokinin levels declined. Seed strains varying in their degree ofdormancy were also analysed for hormone levels; a significantly higher level of cytokinin activity was found in the most dormant strain compared with the least dormant strain. Low levels of bound hormones, including cytokinin ribotides and gibberellin glucose conjugates. were detected following enzyme hydrolysis but neither class of compounds varied greatly in level during afterripening.The major cytokinins detected in Auetlo firtrrrr seeds cochromatographed with zeatin-9glucoside, zeatin riboside, and zeatin on both HPLC columns and chromatography paper. The major gibberellin activity cochromatographed with GA,/GA, on silica gel partition columns and thin-layer plates.Germination studies demonstrated that GA,,, is significantly moreactive than GA, in promoting the germination of dormant Au~nrr ffrtirrr seeds. External applications of cytokinins were not found to affect the germination of dormant seed, but did promote germination in partially afterripened material. TAYLOR, J. S., et G. M. SIMPSON. 1980. Endogenous hormones in afterripening wild oat (AUPIIO frrtrrri) seed. Can. J. Bot. 58: 1016-1024. Les niveaux de giberellines et de cytokinines dans les graines en dormance d'Auet~rr fc~trrrr L . ont ete mesures par des tests biologiques durant la post-maturation. Peu d e changements dans les niveaux des deux hormones ont etC decelks dans lagraine seche. Cependant, apres I'imbibition d e la graine ayant termine sa post-maturation. le niveau des giberellines augmente tandis que celui des cytokinines diminue. Les niveaux d'hormones ont aussi ete analyses dans des graines qui different par leur degre d e dormance; on trouve une plus grande activite des cytokinines dans les graines manifestant la plus forte dormance que dans celles dont la dormance est la plus faible. De faibles niveaux d'hormones liees, y compris des ribotides de cytokinine et des composes d e giberelline et glucose, ont ete deceles apres une hydrolyse des enzymes, mais aucune de ces classes de composes ne varie beaucoup durant la post-maturation.Les principales cytokinines decelees dans les graines d'Auet~ufiltlla par co-chromatographie sur papier et sur colonnes de HPLC sont le zeatine-9-glucoside, le riboside d e zeatine et la zeatine. La principale activite giberellinique determinee par co-chromatographie sur colonnes d e gel de silicate et sur couches minces est GA,/GA,.Des etudes de germination montrent que la germination des graines dormantes d'Auetlrifrrturr est facilitle par le GA,,, plus que parle GA,. L'application externe d e cytokinines n'...

The physiological basis of seed dormancy in Avena fatua III. Action of nitrogenous compounds

“…Dormant seed of A. fatua lacked the ability to synthesize or release gibberellins in amounts sufficient to allow germination when imbibed in water (Simpson 1965). Since exogenous application of GA3 breaks dormancy (Naylor and Simpson 1961), and dormant seeds apparently acquire the ability to synthesize gibberellins as they after-ripen and lose dormancy (Taylor and Simpson 1980) the dormant state may be attributed in part to an inability to synthesize gibberellins. The presetit findings show that nitrate-, or nitrite-induced gennination is inhibited by CCC, an inhibitor of gibbereilin biosynthesis (Ninnemann et al 1964).…”

The Biology of Canadian Weeds. 27.Avena fatuaL. (updated)

“…GA 3 was more effective than fusicoccin, a diterpene glycoside, in releasing dormancy in A. fatua genotypes (Foley 1986). GA 4/7 was more active than GA 3 in promoting germination of dormant seeds (Taylor and Simpson 1980). Ethanol (C 2 H 6 O) solution (50Á200 mM), and to a lesser extent, sodium azide (NaN 3 ) and nitrate (NaNO 3 ), each involved in GA biosynthesis, promoted seed germination of four dormant A. fatua genotypes (Adkins et al 1984).…”

“…Increasing levels of endogenous inorganic P within the seed influenced dormancy release and germinability during afterripening (Quick et al 1997). Following imbibition of fully afterripened seed, GA levels increased while cytokinin levels declined (Taylor and Simpson 1980). A number of controlled environment (Petri dish) studies have examined environmental conditions affecting seed dormancy and germination.…”

Breakage of Seed Dormancy of Field Pennycress (Thlaspi arvense) by Growth Regulators, Nitrate, and Environmental Factors

“…Although these differences may arise from dif ferential uptake of various gibberellins, other explanations are also possible. In wild oat seed the major endogenous gibberellins appear to be GA 4 and GA 7 (11), and in some seed, GA 4+7 has been shown to be a more potent dormancy breaking agent than GA 3 (2,7,11). In view of the fact that in our experiments GA 4+7 bypassed the requirements for all other factors, it is possible that GA 4 and/or GA 7 are the primary endogenous factors that overcome dormancy in field pennycress; and factors such as light, temperature manipulations, and nitrate serve to increase the endogenous level or the activity of GA 4+7 .…”