Germination of Solanum lycocarpum St. Hil seeds: mechanism and regulation / GerminaÃÃo de sementes de lobeira (Solanum lycocarpum St. Hil): Mecanismo e regulaÃÃo

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The aims of this study were i) to determine the method to collect fruits at field condition, ii) to define the best germination condition, iii) to characterize morphologically the fruits and morpho-anatomically the seeds, iv) to study the germination mechanism of the seeds, v) to study the control of this process by ABA and vi) to compare the mechanism and regulation of germination of S. lycocarpum and tomato seeds. The results showed that fruits of S. lycocarpum must be dispersed after natural dispersion. The best germination condition found was by alternating light/dark and temperature (20-30ÂC), 12 hours. The effect of the alternation of temperature during the germination is in endosperm cap. The fruit is a berry, greenish even when mature, with fleshy, yellowish, fragrant endocarp. The seeds (545 per fruit, in average) have a rigid, dark-brown seed coat which does not avoid water uptake. The embryo is spiralled, encircled by the endosperm, with the cotyledons at the inner part and the hypocotyl and radicle, curved, at the outer part. The endosperm cap has 7-8 layers of elongated polygonal cells with average diameter and cell wall thickness statistically lower than those of the cells of the lateral endosperm. After a prolonged period at the phase II of imbibition, the embryos isolated from seeds imbibed in water showed a significant increase of fresh weight before radicle protrusion coinciding with the rupture of the seed coat, but not of the endosperm, which is only ruptured after seeds remain under germination conditions for 1-2 more days. The puncture force of the endosperm cap showed two stages of significant decrease throughout the imbibition course in water. The activity of endo-b-mannanase in water-imbibed seeds started after the first day of imbibition and increased throughout the imbibition course. The puncture force of the endosperm cap showed significant correlation with the increase of the activity of endo-b-mannanase. Before radicle protrusion, activity of endo-b-mannanase occurred only in the endosperm cap in water-imbibed seeds. Activity of this enzime in the lateral endosperm was observed only after radicle protrusion. ABA inhibited the increase of the embryo weight after the begginning of phase II of imbibition, the second stage of weakening of the endosperm cap and the activity of endo-b-mannanase in the endosperm cap throughout the imbibition course. In the presence of ABA, seeds of S. lycocarpum behaved similarly to the tomato seeds, considering the second stage of decrease in the rupture force of the endosperm cap, the activity of endo-b-mannanase and its location. Thus, the weakening of the endosperm cap is necessary for the germination of S. lycocarpum seeds which occurs in two stages. The first and the second stages coincide with the increase of the activity of endo-b-mannanase, with the embryo contributing to the second stage through increasing its fresh weight which indicates increase of the pressure potential of its cells, before radicle protrusion.

ASSUNTO(S)

morfo-anatomia sementes florestais morpho-anatomy, weakening endosperma micropilar Ãcido abscÃsico endosperm cap, pressure potential endo-b-mananase potencial de pressÃo endo-b-mannanase, abscisic acid amolecimento

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