Abstract:Over the past twenty years many studies have been undertaken to elucidate the regulation of seed germination. Abscisic acid (ABA) and the gibberellins (GAs) are the hormones proposed to control this process, the first by inhibiting and the second by inducing germination. It has been proposed that a high water potential increases the growth potential of the embryo, presumably permitting the production or activation by GA of the cell wall hydrolases and thus decreasing the yield threshold of the endosperm close … Show more
“…The ABAa decline in 25 to 40 DAA seeds occurred prior to radicle protrusion. The slight increase in ABAa measured after radicle protrusion in all seed ages was attributed to de novo synthesis associated with radicle growth, as observed previously by Iglesias and Babiano (1997). Figure 4Patterns of endogenous abscisic acid in the embryonic axes (ABAa) during incubation of immature intact soybean seeds harvested at 25, 30, 35, 40 and 45 d after anthesis (DAA).…”
Section: Resultssupporting
confidence: 85%
“…The ABAa decline in 25 to 40 DAA seeds occurred prior to radicle protrusion. The slight increase in ABAa measured after radicle protrusion in all seed ages was attributed to de novo synthesis associated with radicle growth, as observed previously by Iglesias and Babiano (1997).…”
The germination of developing seeds is very uncommon and is generally associated with deficiencies in abscisic acid (ABA) synthesis or sensitivity. This paper examines the quantitative relationship between the inhibition of precocious germination and endogenous ABA in the embryonic axis (ABAa) of hydrated soybean [Glycine max (L.) Merr.] seeds, isolated after the completion of histodifferentiation and before the beginning of dehydration, as well as the magnitude and evolution of axis sensitivity to endogenous ABA during that period. Developing seeds harvested at 25, 30, 35, 40 and 45 d after anthesis (DAA) were subjected to incubation or washing to induce changes in ABA content. ABA content was measured by radioimmunoassay, using a monoclonal antibody against free ABA. Germinability was measured as the time to 50% germination (t 50 ). Washing and incubation induced eight-and twofold increases, respectively, in the rate of ABAa decline compared with the in planta ABAa decline. The threshold ABAa for inhibition of precocious germination (ABAc) increased slightly from 25 to 40 DAA [1.15 -1.66 mg ABA (g DW) 21 ]. This contrasted with the substantial decline in ABAa [10.90 -2.07 mg ABA (g DW) 21 ] during the same period, and indicated that sensitivity to endogenous ABA of hydrated seeds was initially high and diminished slowly during development. The relationship between (ABAa -ABAc) and t 50 was linear for immature seeds incubated before and after washing. Below the ABAc, there were no differences in the t 50 of 25 -45 DAA seeds. The ABAa contribution to the control of precocious soybean seed germination was evident, although other potentially interacting factors were also present.
“…The ABAa decline in 25 to 40 DAA seeds occurred prior to radicle protrusion. The slight increase in ABAa measured after radicle protrusion in all seed ages was attributed to de novo synthesis associated with radicle growth, as observed previously by Iglesias and Babiano (1997). Figure 4Patterns of endogenous abscisic acid in the embryonic axes (ABAa) during incubation of immature intact soybean seeds harvested at 25, 30, 35, 40 and 45 d after anthesis (DAA).…”
Section: Resultssupporting
confidence: 85%
“…The ABAa decline in 25 to 40 DAA seeds occurred prior to radicle protrusion. The slight increase in ABAa measured after radicle protrusion in all seed ages was attributed to de novo synthesis associated with radicle growth, as observed previously by Iglesias and Babiano (1997).…”
The germination of developing seeds is very uncommon and is generally associated with deficiencies in abscisic acid (ABA) synthesis or sensitivity. This paper examines the quantitative relationship between the inhibition of precocious germination and endogenous ABA in the embryonic axis (ABAa) of hydrated soybean [Glycine max (L.) Merr.] seeds, isolated after the completion of histodifferentiation and before the beginning of dehydration, as well as the magnitude and evolution of axis sensitivity to endogenous ABA during that period. Developing seeds harvested at 25, 30, 35, 40 and 45 d after anthesis (DAA) were subjected to incubation or washing to induce changes in ABA content. ABA content was measured by radioimmunoassay, using a monoclonal antibody against free ABA. Germinability was measured as the time to 50% germination (t 50 ). Washing and incubation induced eight-and twofold increases, respectively, in the rate of ABAa decline compared with the in planta ABAa decline. The threshold ABAa for inhibition of precocious germination (ABAc) increased slightly from 25 to 40 DAA [1.15 -1.66 mg ABA (g DW) 21 ]. This contrasted with the substantial decline in ABAa [10.90 -2.07 mg ABA (g DW) 21 ] during the same period, and indicated that sensitivity to endogenous ABA of hydrated seeds was initially high and diminished slowly during development. The relationship between (ABAa -ABAc) and t 50 was linear for immature seeds incubated before and after washing. Below the ABAc, there were no differences in the t 50 of 25 -45 DAA seeds. The ABAa contribution to the control of precocious soybean seed germination was evident, although other potentially interacting factors were also present.
“…Results from physiological studies with biosynthetic inhibitors of, and mutants defective in, ABA and GA biosynthesis are largely consistent with the predictions of the model. Measures of endogenous ABA flux, while few, are consistent with the model (Toyomasu et al, 1994;Grappin et al, 2000), although exceptions are known (Iglesias and Babiano, 1997). Over-and antisense-expression of the ABA biosynthetic gene, ABA2, in Nicotiana plumbaginifolia produces plants with seed phenotypes that are consistent with the theory that ABA plays an important role in maintaining dormancy (Frey et al, 1999).…”
Section: Hormone and Inhibitor Bioassays And Hormone Balance Theorymentioning
The native tobacco, Nicotiana attenuata, synchronizes its germination with the immediate post-fire environment with a combination of germination stimulants found in wood smoke and inhibitors from the unburned litter of the dominant vegetation. The inhibitors override the stimulants and prevent seeds from germinating maladaptively in unburned habitats adjacent to burns. To understand the physiological basis of this environmental control of germination, we tested several previously isolated signals, phytohormones and their respective biosynthesis inhibitors. The germination inhibitors methyl jasmonate (MeJA, a constituent of sagebrush litter), bornane-2,5-dione (BD, a constituent of juniper litter extract, JLE) and JLE did not alter abscisic acid (ABA) content of imbibed seeds. Treatment with the ABA biosynthesis inhibitor, fluridone, inhibited the dormancyinducing effects of BD, JLE and MeJA, but surprisingly did not affect endogenous ABA levels in treated seeds. However, ABA leached from litter of the species, which dominate the plant community before fires, plays an important role in germination control. We conclude that N. attenuata seeds, which can lie dormant in the soil for 150 years between fires, time their germination with the post-fire environment by responding to smoke, ABA and four terpenes (BD, 1,8-cineole, β-thujaplicin and camphor) leaching from the litter of the dominant vegetation.
“…The dormant corms or seeds need cold treatment for long period of time to break dormancy which is a limiting factor in this approach (Dole, 2003). On the other hand, plant growth regulators such as benzyladenine, gibberellic acid and indole acetic acid have been reported to short the dormant period by facilitating germination (Hilhorst and Karssen, 1992;Iglesias and Babiano, 1997;Cirak et al, 2007;Finkelstein et al, 2008). Exogenous application of gibberellic acid is an alternative of cold treatment and effective in shortening the dormancy period of gladiolus corms (Ginzburg, 1974;Tonecki, 1980;Bhattacharjee, 1984;Dua et al, 1984).…”
Gladiolus is commercially propagated through corms and occurrence of dormancy in freshly harvested corms creates hindrance in their cultivation. Present study was designed to compare the effect of different chemicals to alleviate the dormancy of corms in a short time. Gladiolus corms were collected from two growing sites and subjected to chemicals methanol, benzylaminopurine (BAP), gibberellic acid (GA3), indole acetic acid (IAA), salicylic acid, potassium nitrate and thiourea at different concentrations alone or in combinations. The treated corms were planted on sand and placed under dark conditions at 26°C. The treatment of 60% methanol in combination with 0.9 mM BAP showed maximum germination (72.71%). Descaled corms showed 85% germination compared to 60.42% scaled corms, while the corms collected from Faisalabad showed better germination 83.75% compared to corms from Rawalakot (61.67%). The application of 60% methanol also induced 29.65% and 42.43% deterioration in scaled and descaled corms, respectively. The treatments of 0.3 mM BAP in combination with 0.6 mM GA3 exhibited 88.33 % germination in corms collected from Faisalabad as compared to 55% in corms from Rawalakot. Overall, application of BAP and GA3 in combination was found effective in shortening the period of dormancy in both cultivars of gladiolus compared to other tested chemicals or growth regulators.
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