Ultrastructure of Early Secondary Embryogenesis by Multicellular and Unicellular Pathways in Cork Oak (Quercus suber L.)

Early cellular events during secondary embryogenesis were studiedin a cork oak recurrent embryogenic system in which embryosarise either in a multicellular budding pathway from a compactmass of proliferation or from isolated single cells in friablecallus. The compact mass of proliferation originated from theepidermal cells at the hypocotyl whose growth and convolutionwas characterized by a decrease in the nucleus/cytoplasm ratioand a marked increase in storage products. The transition fromthe compact mass to meristematic primordia occurred at the peripheryand was accompanied by cell dedifferentiation and a drasticreduction of storage products. Meristematic primordia evolvedto globular embryos by the organization of a protodermis andtwo internal centres. Microscope analysis of friable callusshowed an hypothetical sequence from single cells to aggregatesof a few cells, meristematic cell clusters and globular embryos.Single cells showed typical features of embryogenic cells suchas rich cytoplasm and a large number of starch grains and lipidbodies. A progressive cell dedifferentiation and a drastic reductionof storage products was observed when aggregates of a few cellsand meristematic cell clusters were compared. Progressive bipolarizationin large meristematic cell clusters initiated globular embryoformation. The comparison of both embryogenic pathways at theultrastructural level showed that subcellular changes followa similar sequential pattern, especially with regard to thestorage products. The possible role of plastid extrusions andmultivesicular bodies in the changing pattern of starch metabolismduring embryogenesis is discussed. Copyright 2001 Annals ofBotany Company Quercus suber L, cork oak, somatic embryogenesis, multicellular budding, friable callus, ultrastructural studies     

Social facilitation of agonistic responses to strangers in pairs of saddle back tamarins (Saguinus fuscicollis)

The effect of the presence of a familiar social partner on the interactions of saddle back tamarins with unfamiliar conspecifics was studied. Fifteen adult male-female pairs, of which six were composed of a castrated male and an intact female, served as subjects. All subject pairs were given two social encounters during which both mates met a strange male and two encounters during which they met a strange female. In addition, all subjects were given four encounters during which they met the same strangers while their own pair mates were absent. As a group, the subjects showed higher intensities of injurious aggression and of agonistic displays when they met strangers in the presence of their own pair mates. Females and castrated males, as subgroups, showed significant increases in most agonistic responses when they met strangers in the presence of their pair mates. Intact males, however, did not.     

Mikrorespirometrische Untersuchungen an höheren Pflanzen. I

Ohne ZusammenfassungMit 2 Textabbildungen.     

Migration timing and distance from shore of southbound eastern Pacific gray whales (Eschrichtius robustus) off Ensenada,Baja California,Mexico

Eastern Pacific gray whales were monitored off Ensenada, Mexico, during the southbound migration. The objectives were to determine southbound migration timing and width of the migration corridor during three seasons (2003–2006). Migration timing was determined by fitting a generalized additive model to the shore counts for each season and estimating the 10, 50, and 90 percentiles of the fitted curves. To estimate abundance from shore‐based counts, a probability density function for the shore based distances was estimated by a product of a gamma distribution fit to the boat survey distance data for 2006/2007 and a half‐normal detection function using combined data of the three seasons. The parameters of the gamma distribution were corrected to account for less boat survey effort carried out 20–40 km than 0–20 km from shore. The onset of the migration off Ensenada was in late December/early January and ended around 13 February. The median date was 23–26 January for the first and third season and a week early for the second season. Boat surveys indicated a wide (20 km) migration corridor but most gray whales traveled within 9.9 km from shore. The estimated total number of whales during watch hours was 2,298 (95% CI = 1,536–4,447).     

Studien über die Entwicklung der Chloroplasten beiAgapanthus umbellatus

Ohne Zusammenfassung