Symplasmic transport and phloem loading in gymnosperm leaves

Despite more than 130 years of research, phloem loading is far from being understood in gymnosperms. In part this is due to the special architecture of their leaves. They differ from angiosperm leaves among others by having a transfusion tissue between bundle sheath and the axial vascular elements. This article reviews the somewhat inaccessible and/or neglected literature and identifies the key points for pre-phloem transport and loading of photoassimilates. The pre-phloem pathway of assimilates is structurally characterized by a high number of plasmodesmata between all cell types starting in the mesophyll and continuing via bundle sheath, transfusion parenchyma, Strasburger cells up to the sieve elements. Occurrence of median cavities and branching indicates that primary plasmodesmata get secondarily modified and multiplied during expansion growth. Only functional tests can elucidate whether this symplasmic pathway is indeed continuous for assimilates, and if phloem loading in gymnosperms is comparable with the symplasmic loading mode in many angiosperm trees. In contrast to angiosperms, the bundle sheath has properties of an endodermis and is equipped with Casparian strips or other wall modifications that form a domain border for any apoplasmic transport. It constitutes a key point of control for nutrient transport, where the opposing flow of mineral nutrients and photoassimilates has to be accommodated in each single cell, bringing to mind the principle of a revolving door. The review lists a number of experiments needed to elucidate the mode of phloem loading in gymnosperms

Atención primaria pregrado

La atención de salud debe ser ambulatoria, y lahospitalización solo cuando sea indispensable, la causason la urbanización y el aumento de la expectativa devida. La tendencia comienza en 1945 en Inglaterra,la Declaración de Alma Ata en 1978 de OMS. EnLatino América 1975 y en Venezuela en 1979. Secreó la Especialidad Médica MEDICINA FAMILIAR,el primer posgrado fue en el Centro Ambulatorio deCaricuao del IVSS por Carmen Cedraro de Carpio yRafael Anselmi 1982. La OPS dirigió la ejecución yel desarrollo. Describimos la estructura curricularMedicina Familiar. En 16 países estudiados haydocencia de APS en pregrado. Hoy debe haber unMédico General-Familiar por cada 500 familias o2 500 personas. Necesitamos 12 000 médicos conposgrado en Medicina Familiar. Son las conclusionesy recomendaciones: 1. La Atención Primaria deSalud (APS) es el eje en la conservación de la salud,la prevención y el tratamiento. 2. La APS debe juntocon la Historia Médica Electrónica ser enseñada en elPregrado de la Facultad Medicina. 3. Creen la OPS yla OMS, que debe ser desempañada por los Municipiosjunto con la Educación Preescolar artículo 178 aparte5 de la Constitución Nacional. 4. La AcademiaNacional de Medicina de Venezuela debe participarloa: 1. Las Facultades y Escuelas de Medicina, 2.Sociedades Científicas de la Especialidades Médicas,y 3. Autoridades Gremiales Colegios de Médicos yFederación Médica.Palabras clave: Atención médica en Ambulatorios; Medicina Familiar a nivel Municipal.SUMMARYThe center of health care must be ambulatory andhospitalization used when is essential. The urbanizationand the increase of life expectancy reinforce the idea.Return to General Physician 1945 in England. TheDeclaration of Alma Ata in 1978 WHO. Health for allin the year 2000. In Latin America 1975 Venezuelain 1979. The family medicine medical specialty wascreated, the first postgraduate program in Venezuelawas in the outpatient center of Caricuao of the IVSS’sby Carmen Cedraro de Carpio and Rafael Anselmi1982. The PAS was the leader in implementationand development for the public welfare. We describecurricular structure of the postgraduate in familymedicine. In 16 countries all there are APS teachingin undergraduate. Should be a General-Familiardoctor 500 families or 2 500 people. Venezuela need12 000 physicians in family medicine. The conclusionsand recommendations: 1.The APS is the base in theconservation of the health, in the prevention andtreatment of diseases. 2. The APS must togetherwith the electronic medical history should be taughtto the undergraduates. 3. Following the thinkingof the PAHO and the WHO should be played by themunicipalities along with preschool education as thea-side says 5 of article 178 of the existing NationalConstitution. 4. These three principles, the NationalAcademy of Medicine of Venezuela must do so in theknowledge of: 1. Faculties and Schools of Medicine,2. Scientific Societies of the Medical Specialties,and 3. Authorities Union Colleges of Physicians andVenezuelan Medical Federation.Key words: Medical Care in Ambulatory; MunicipalFamily Medicin