Effect of ethylene on auxin transport and metabolism in midrib sections in relation to leaf abscission of woody plants

Abstract The relationship between ethylene-induced leaf abscission and ethylene-induced inhibition of auxin transport in midrib sections of the leaf blade of Citrus sinensis L. Osbeck, Populus deltoides Bart, and Eucalyptus camaldulensis Dehn. was studied. These species differed greatly in their abscission response to ethylene. The kinetic trend of abscission resembled that of the inhibition of auxin transport in all three species. It is suggested that one of the main actions of ethylene in the leaf blade is to inhibit auxin transport in the veinal tissues, thus reducing the amount of auxin transported from the leaf blade to the abscission zone. Ethylene inhibited transport of both IAA (indole-3-acetic acid) and NAA (α-naphthaleneacetic acid) in the midrib sections. However, while ethylene enhanced the conjugation of IAA with aspartic acid and glucose in the apical (absorbing) segment of the midrib sections, it had little effect on the conjugation of NAA. The data indicate that auxin destruction through conjugation does not play a major role in the inhibition of auxin transport by ethylene.     

Microbial diversity and community structure in Fynbos soil

The Fynbos biome in South Africa is renowned for its high plant diversity and the conservation of this area is particularly important for the region. This is especially true in the case of endangered vegetation types on the lowlands such as Sand Fynbos, of which only small fragments remain. The question is thus whether the diversity of the above‐ground flora is mirrored in the below‐ground microbial communities. In order to determine the relationship of the above‐ and below‐ground communities, the soil community composition of both fungal and bacterial groups in Sand Fynbos was characterized over space and time. A molecular approach was used based on the isolation of total soil genomic DNA and automated ribosomal intergenic spacer analysis of bacterial and fungal communities. Soil from four different sites was compared to resolve the microbial diversity of eubacterial and fungal groups on a local (alpha diversity) scale as well as a landscape scale (beta diversity). The community structures from different sites were compared and found to exhibit strong spatial patterns which remained stable over time. The plant community data were compared with the fungal and the bacterial communities. We concluded that the microbial communities in the Sand Fynbos are highly diverse and closely linked to the above‐ground floral communities.     

A requirement for protein synthesis during the curvature of citrus petals

The opening of citrus petals is an auxin mediated process. Inhibition of curvature by antimetabolites of nucleic acidsand protein synthesis can be partially relieved by the correspondingmetabolites. Cycloheximide inhibited curvature and incorporationof ¹⁴C-leucine into protein by more than 80%. IAA did not enhanceincorporation significantly, but the auxin antagonist p-chlorophenoxyisobutyricacid did inhibit it to a certain extent. On opening petals graduallylose the ability to synthesize protein. (Received November 4, 1970; )     

Diphenylhydantoin reverses Membrane Effects in Steroid Myopathy

THE induction of a myopathy in laboratory animals by long term administration of corticosteroids is well documented histologically¹ and histochemically². Changes in type II (fast) muscle fibre membrane properties also occur and result in depolarization and a shift, in the hyperpolarized direction, of the potential-dependent membrane excitability³. These changes in membrane properties may result, at least in part, from alterations in transmembrane electrolyte concentrations or permeabilities, possibly by affecting the operation of the active Na transport mechanism. Since diphenylhydantoin has been shown to alter membrane permeability to Na+ (refs. 4–6) and to cause an increase in intracellular K⁺ concentration⁷, it was of interest to determine its effects on muscle fibres from steroid-treated mice.