Reproductive biology of the "Brazilian pine" (Araucaria angustifolia-Araucariaceae): the pollen tube growth and the seed cone development.

KEY MESSAGE: In Araucaria angustifolia, the seed scale is part of the ovule, the female gametophyte presents a monosporic origin and arises from a coenocytic tetrad, and the pollen tube presents a single axis. The seed cone of conifers has many informative features, and its ontogenetic data may help interpret relationships among function, development patterns, and homology among seed plants. We reported the seed cone development, from pollination to pre-fertilization, including seed scale, ovule ontogeny, and pollen tube growth in Araucaria angustifolia. The study was performed using light microscopy, scanning electron microscopy, and X-ray microcomputed tomography (µCT). During the pollination period, the ovule arises right after the seed scale has emerged. From that event to the pre-fertilization period takes about 14 months. Megasporogenesis occurs three weeks after ovule formation, producing a coenocytic tetrad. At the same time as the female gametophyte's first nuclear division begins, the pollen tube grows through the seed scale adaxial face. Until maturity, the megagametophyte goes through the free nuclei stage, cellularization stage, and cellular growth stage. Along its development, many pollen tubes develop in the nucellar tissue extending straight toward the female gametophyte. Our observations show that the seed scale came out of the same primordia of the ovule, agreeing with past studies that this structure is part of the ovule itself. The formation of a female gametophyte with a monosporic origin that arises from a coenocytic tetrad was described for the first time in conifers, and the three-dimensional reconstruction of the ovule revealed the presence of pollen tubes with only one axis and no branches, highlighting a new pattern of pollen tube growth in Araucariaceae.

Quality of castor bean seeds (Ricinus communis l) affected by raceme and fruit position during storage / Posição do racemo e do fruto na qualidade fisiológica de sementes de mamona durante o armazenamento

The present research had as objective to evaluate the influence of raceme and fruit position on physiological quality of castor bean seeds (Ricinus communis L.) during storage of cultivar AL Guarany 2002.  The treatments were: position of the raceme in plants (primary, secondary and tertiary) and position of fruit in racemes (low, medium and high). After fruit extraction, seeds were stored under environmental conditions for twelve months. The experimental design used was the completely randomized in a split-plot arrangement. Main plots consisted of the interaction raceme x fruit position and subplots were the storage time. Physiological quality was evaluated quarterly through tests of moisture content, germination and vigor (first count, accelerated aging, seedling length and seedling dry matter). Neither the position of racemes in the plant nor fruit in racemes does not affect germination of castor bean seeds. Dormancy of castor bean seeds decreases during storage, but also increases percentage of abnormal seedlings, seedling dry matter and root, hypocotyl and seedling total length.

O trabalho teve por objetivo determinar a influência da posição do racemo na planta, do fruto no racemo e do armazenamento na qualidade fisiológica de sementes de mamona (Ricinus communis L.) da cultivar AL Guarany 2002. Os tratamentos foram: posição do racemo na planta (primário, secundário e terciário) e posição dos frutos no racemo (inferior, médio e superior). Depois da extração dos frutos, as sementes foram armazenadas em condições ambientais para avaliações trimestrais de qualidade fisiológica até os doze meses. O delineamento experimental utilizado foi o inteiramente casualizado com parcelas subdivididas. Na parcela foi estudado o fatorial e nas subparcelas os tempos de armazenamento. Foram determinados no momento da colheita e aos três, seis, nove e doze meses o grau de umidade das sementes, a germinação e o vigor (primeira contagem do teste de germinação, envelhecimento acelerado, crescimento e massa de matéria seca de plântulas). A posição do racemo e dos frutos no racemo em mamoneira não influencia a porcentagem de germinação de sementes de mamoneira. Com o decorrer do armazenamento a dormência das sementes diminui e aumenta a porcentagem de plântulas anormais, a massa de matéria seca, o comprimento total, de raiz e de hipocótilo das plântulas.