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

Knowledge, attitudes and beliefs of primary caretakers towards Sickle Cell anaemia in children

The objective of this study was to evaluate knowledge, attitudes and beliefs (KAB) that may influence health seeking behaviour of caretakers of children with sickle cell disease (SCD). A cross-sectional survey was undertaken at Nyanza provincial hospital in Kenya between March and September 1993 to identify socio-demographic and economic factors that may influence health seeking behaviour of primary caretakers of children with SCD. All caretakers accompanying children under the age of 18 years to the Sickle Cell Clinic were eligible. Guardians accompanying children to the clinic were interviewed using pretested questionnaires. An exploratory factor analysis method was used to categorise questionnaire items into domains (knowledge, attitude and belief) and to investigate for association between certain socio-demographic factors and KAB. Seventy five per cent of the 108 respondents interviewed were mothers and 16.7% fathers. Seventy eight percent knew SCD to be hereditary while 55% knew how the disease presents in childhood. Only 42% associated SCD with increased risk of infection. Many felt severe infections are largely preventable and that prevention would reduce their anxiety and illness related costs. In factor analysis, variables loaded almost exclusively on Attitudes and Beliefs factors. Only family size was found to influence caretaker attitudes (p = 0.0095) and beliefs (p = 0.0034). Education, monthly income, occupation and religion had no significant influence. The majority of caretakers had good knowledge and positive attitudes towards SCD in children. Interventions aimed at management of SCD or prevention of its sequelae would be well accepted. Factor analysis is recommended for statistical analysis of KAB data. The effect of family size on attitudes and behaviour needs further evaluation

Replication timing: histone genes replicate during early S phase in cleavage-stage embryos of sea urchin.

Newly synthesized DNA was separated from the bulk of the DNA by pulse-labeling with BUdR and centrifugation in an alkaline CsCl buoyant density gradient. The content of histone gene in the newly synthesized DNA was determined by DNA dot hybridization. The gene contents in DNA replicated during the early half of S phase and during the whole S phase were compared. Results showed that histone genes were replicated during the first half of the S phase in embryos in the early cleavage stage

KUCA critical experiments using MEU fuel (II)

Due to mutual concerns in the USA and Japan about the proliferation potential of highly-enriched uranium (HEU), a joint study program was initiated between Argonne National Laboratory (ANL) and Kyoto University Research Reactor Institute (KURRI) in 1978. In accordance with the reduced enrichment for research and test reactor (RERTR) program, the alternatives were studied for reducing the enrichment of the fuel to be used in the Kyoto University High Flux Reactor (KUHFR). The KUHFR has a distinct feature in its core configuration: it is a coupled-core. Each annular shaped core is light-water-moderated and placed within a heavy water reflector with a certain distance between them