Dormência e germinação de coquinho-azedo: substâncias inibidorasnos pirênios e morfoanatomia dos embriões e de plântulas

Abstract

In palm trees, the morphological dormancy and the germination-inhibiting substances are topics rarely studied. Thus, this research has as aim, to evaluate the inhibitory effect on germination and the chemical composition of extracts from the endocarp and endosperm of coquinho-azedo, besides to characterize, morph-anatomically, the zygotic embryo of this species, relating it to the morphological dormancy and describe features indicative of germination and of the seedling development. Extracts were prepared from the endocarp and endosperm, using three solvents in increasing polarity: hexane, ethyl acetate and methanol. The extracts were applied to lettuce seeds. The chemical constituents of the methanol extracts were identified by gas chromatography coupled to mass spectrometry. It was found that the methanol extract of the endosperm and endocarp influenced negatively the growth of hypocotyl and radicle, but no effect of extracts on the percentage and in the index of germination rate, fresh and dry matter of radicle and hypocotyl. The main substances identified with potential allelopathic were: esters (Z) octadec-9-enoate of methyl, methyl hexadecanoate and the acids dodecanoic, decanoic, tetradecanoic, octanoic, (Z) octadec-9-enoic, hexadecanoic, (9Z, 12Z)-octadeca-9,12-dienoic. The embryos of coquinho-azedo were cultivated in vitro, removing them from the medium at various times for the morphoanatomical analysis. Embryos showed a conical shape, with 3.7 mm in length on average and have the following meristematic tissues: protoderm, fundamental meristem, procambium; plumule and hypocotyl-radicle axes differentiated. In distal region, we observed the haustorium, which atrophies into the cultivation medium. Already on the second day in vitro culture, we observed an increase in the volume of cells, elongation of embryonic axis and beginning of differentiation of the first eophyll. From second to fifth day, we verified the elongation of the cotyledon petiole and the differentiation of the parenchyma. On the eighth day there was protrusion of the root. From twelfth to the sixteenth day, there was the emission of the sheaths. Seeds of coquinho-azedo were sown in beds, being collected at different stages for describing the morphological aspects of germination. In the cultivating in bed, occurs initially swelling of the embryo, which shifts the operculum, culminating in the issuance of the cotyledon petiole. This petiole elongates itself to form an acute structure, from where emerge the roots and the first sheath. Subsequently, there is the emission of the second sheath, of the first eophyll and secondary roots. We conclude that, from the second day of cultivation, it is possible to verify anatomic changes in the embryonic axis and that the morphological dormancy is not the predominant factor for the low germination rates of coquinho-azedo.