Morfoanatomia do desenvolvimento do fruto de Isertia hypoleuca Benth. (Rubiaceae - Cinchonoideae)

Abstract

Isertia is a peculiar genus of Rubiaceae due to its association with secondary tropical forests and recovering forests. It is represented by fifteen species distributed mainly in the rainforests of Central and South America. The morphological peculiarities and the inaccurate use of terminology and typology of Isertia hypoleuca Benth. fruits tends to hinder their classification. Thereby, morphological and anatomical aspects of pericarp and seeds of I. hypoleuca were studied in order to establish the main ontogenetics stages of fruit development, leading to the correct interpretation of its typology. Four stages were registered which main characteristics of each of them are associated with endocarp and exotesta sclerification and seed tissues development. Isertia hypoleuca shows inferior ovary, sincarpic with four to six multi-locular ovary, axial placentation with hemianatrop ovum inserted all along the septum extension. The stage 1 is represented with a newly formed fruit within 1 to 20 days, the exocarp shows maroon coloring, the mesocarp is consistent and the endocarp is undifferentiated. The uniseried mesocarp cell wall shows papilous cells and polyhedral glands. The mesocarp is parenquimatic with many drusen and idioblasts. The endocarp contains about five cell layers in intense process of anticlinal division. The seed is unitegumented and there is intense meristematic activity in the mesotesta. At this stage, the moisture content is the highest, 86.92%. In stage II, the fruit has 77-97 days, exocarp colloring is yellowish green, cored and the exotesta starts the sclerification process. Stage III, fruit with 90 to 210 days, is marked by a sharp sclerification of the endocarp and seed coat, due to the development of endotesta. The endosperm and embryo are well developed. At this stage the fruit has the largest size. In stage IV the fruit is ripe, with 230-250 days, the odor is very similar to the acaí and the color is the deep violet. A reduction of the fruit size occurs showing 9.56 x 8.80 mm, and also the lowest moisture content 31.9% is observed. The exocarp is formed by pericarp wall and underlying mesocarp cells. The mesocarp region corresponding to the fleshy pulp mass comprise a completely or partially disintegrated cells, idioblasts and fibers. The endocarp is osseous and forms four to six pyrenes polispermes disconnected between each other. The seeds are reddish brown angular, with 1 mm, showing a thick testa with foveolad aspect, the endosperm is fleshy. The embryo is white, cylindrical and opaque and occupies the central area of the seed. Based on morphogenesis, the fruit of I. hypoleuca was classified as drupe.