Effect of the seed coat on dormancy and germination in <i>Stylosanthes humilis</i> H. B. K. Seeds

Seed of Townsville stylo (Stylosanthes humilis H.B.K.) is known to exhibit a hard seed coat and when freshly harvested also show a physiological dormancy, however, the nature of the co-actions between seed coat and embryo growth that determine dormancy is poorly understood. In this study, physical dormancy of Townsville stylo seeds was not reduced during natural ageing at room temperature, in contrast to the physiological dormancy, which is gradually overcome during after-ripening. Furthermore, the permeability of seed coat was affected by scarification treatments as well as by low-pH solutions. Together, these data indicate that physical dormancy overcome of seed is prerequisite for radicle protrusion and physiological dormancy of Townsville stylo seeds contribute to its timing.

Index terms:
physical dormancy; physiological dormancy; Townsville stylo

Authorship

Izabel de Souza Chaves ^**Corresponding author izabelchaves@yahoo.com.br

Departamento de Biologia Vegetal, Universidade Federal de Viçosa, 36570-900 - Viçosa, MG, Brasil.Universidade Federal de ViçosaBrazilViçosa, MG, BrazilDepartamento de Biologia Vegetal, Universidade Federal de Viçosa, 36570-900 - Viçosa, MG, Brasil.

Nilo Cesar Queiroga Silva

Dimas Mendes Ribeiro

*Corresponding author izabelchaves@yahoo.com.br

SCIMAGO INSTITUTIONS RANKINGS

Figures | Tables

Figures (5)
Tables (1)

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Figure 1
Effect of dry storage on dormancy release of Townsville stylo seeds. (a) Germination was determined in mechanically scarified seeds imbibed just in water or in intact seeds treated with ACC (1 mM), CEPA (1 mM) and ethylene gas (10 μM). (b) Permeability of intact seeds to tetrazolium solution. Remaining fraction of seed to 100% corresponds to impermeable seeds. Germination and permeability of seeds to tetrazolium salt were carried out on the 5^th day. Values with the same letter within (a) each natural aging time and (b) among natural aging time are not statistically different at the 5% level by Tukey test. Data points are means of five replicates ± standard error.

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Figure 2
Scanning electron micrographs of Townsville stylo seed. (a) Entire mature seeds (15 post-harvest days old) showing radicle tip (r), cotyledons (c) and seed coat (sc). (b,c and d) Structure of the seed coat showing cuticle (cu), palisade layer (p), endothelium layer (e), crushed parenchymatic layer (cp) and cotyledons (c).

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Figure 3
Scanning electron micrographs of Townsville stylo seed coat after pre-treatment with different dormancy breaking methods. (a) Intact seeds (15 post-harvest days old) showing hilum (h) and micropyle (m); (b) mechanical scarification with fine sand paper. Detail shown the damage caused by sandpaper occurs preferentially in the curved region and at the extremity where the protrusion of the radicle occurs; (c and d) acid scarification with H₂SO₄ for 1 and 5 min, respectively. (e) Cracks are see on the surface of seeds treated with H₂SO₄ for 1 min. (f and g) Morphology of the hilum area after treatment with H₂SO₄ for 5 min.

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Figure 4
Time course of germination for dormant seed (15 post-harvest days old) and non-dormant seed (765 post-harvest days old) after pre-treatment with different physical dormancy breaking methods. (a, b, c and d) Seeds were imbibed in water (filled circle) or 1 mM CEPA (open circle). (e and f) Seeds were pre-treated with H₂SO₄ for 1 and 5 min, and imbibed in water (open diamond, open square) or 1 mM CEPA (filled diamond, filled square), respectively. Data points are means of five replicates ± standard error.

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Figure 5
Response of Townsville stylo seeds to MacIlvaine buffer solutions at several pH(s). (a and b) Permeability of intact seed to tetrazolium salt supplied in MacIlvaine buffer at several pH(s). Remaining fraction of seed to 100% corresponds to impermeable seeds. (c and d) Germination of seeds incubated in serial pH MacIlvaine buffer solutions. Test-solutions were renewed 24 hours after start of imbibition. Permeability of seeds and germination were registered on the 5th day. After mechanical scarification, permeability of seed coat to tetrazolium salt supplied in MacIlvaive pH 7.0 was 95 ± 0.9% and 93 ± 0.7% in dormant (15 post-harvest days old) and non-dormant seeds (765 post-harvest days old), respectively. Bars followed by the same small or capital letter across the range of MacIlvaine solutions do not differ statistically at the 5% level by Tukey test.

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Table 1
Permeability of Townsville stylo seed coat to tetrazolium solution and germination of dormant (15 post-harvest days old) and non-dormant (765 post-harvest days old) seeds after treatment with different physical dormancy breaking methods. Permeability of seeds and germination were carried out on the 5th day.

Figure 1 Effect of dry storage on dormancy release of Townsville stylo seeds. (a) Germination was determined in mechanically scarified seeds imbibed just in water or in intact seeds treated with ACC (1 mM), CEPA (1 mM) and ethylene gas (10 μM). (b) Permeability of intact seeds to tetrazolium solution. Remaining fraction of seed to 100% corresponds to impermeable seeds. Germination and permeability of seeds to tetrazolium salt were carried out on the 5^th day. Values with the same letter within (a) each natural aging time and (b) among natural aging time are not statistically different at the 5% level by Tukey test. Data points are means of five replicates ± standard error.

Figure 2 Scanning electron micrographs of Townsville stylo seed. (a) Entire mature seeds (15 post-harvest days old) showing radicle tip (r), cotyledons (c) and seed coat (sc). (b,c and d) Structure of the seed coat showing cuticle (cu), palisade layer (p), endothelium layer (e), crushed parenchymatic layer (cp) and cotyledons (c).

Figure 3 Scanning electron micrographs of Townsville stylo seed coat after pre-treatment with different dormancy breaking methods. (a) Intact seeds (15 post-harvest days old) showing hilum (h) and micropyle (m); (b) mechanical scarification with fine sand paper. Detail shown the damage caused by sandpaper occurs preferentially in the curved region and at the extremity where the protrusion of the radicle occurs; (c and d) acid scarification with H₂SO₄ for 1 and 5 min, respectively. (e) Cracks are see on the surface of seeds treated with H₂SO₄ for 1 min. (f and g) Morphology of the hilum area after treatment with H₂SO₄ for 5 min.

Figure 4 Time course of germination for dormant seed (15 post-harvest days old) and non-dormant seed (765 post-harvest days old) after pre-treatment with different physical dormancy breaking methods. (a, b, c and d) Seeds were imbibed in water (filled circle) or 1 mM CEPA (open circle). (e and f) Seeds were pre-treated with H₂SO₄ for 1 and 5 min, and imbibed in water (open diamond, open square) or 1 mM CEPA (filled diamond, filled square), respectively. Data points are means of five replicates ± standard error.

Figure 5 Response of Townsville stylo seeds to MacIlvaine buffer solutions at several pH(s). (a and b) Permeability of intact seed to tetrazolium salt supplied in MacIlvaine buffer at several pH(s). Remaining fraction of seed to 100% corresponds to impermeable seeds. (c and d) Germination of seeds incubated in serial pH MacIlvaine buffer solutions. Test-solutions were renewed 24 hours after start of imbibition. Permeability of seeds and germination were registered on the 5th day. After mechanical scarification, permeability of seed coat to tetrazolium salt supplied in MacIlvaive pH 7.0 was 95 ± 0.9% and 93 ± 0.7% in dormant (15 post-harvest days old) and non-dormant seeds (765 post-harvest days old), respectively. Bars followed by the same small or capital letter across the range of MacIlvaine solutions do not differ statistically at the 5% level by Tukey test.

Table 1 Permeability of Townsville stylo seed coat to tetrazolium solution and germination of dormant (15 post-harvest days old) and non-dormant (765 post-harvest days old) seeds after treatment with different physical dormancy breaking methods. Permeability of seeds and germination were carried out on the 5th day.

In each column, means do not differ significantly at the 5 % level by Tukey test, when followed by the same letter. Data are means ± standard error of five replicates.

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