Rainfall reliability, a neglected factor in explaining convergence and divergence of plant traits in fire-prone mediterranean-climate ecosystems

Aim Rainfall reliability has been neglected as a determinant of plant trait convergence and divergence in mediterranean‐climate ecosystems. This paper reports on patterns of rainfall reliability — quantified as interannual variation in monthly and seasonal rainfall, and as the frequency of individual events in terms of their size, duration and intensity — for four fire‐prone mediterranean‐climate ecosystems. Location The four mediterranean‐climate regions of the world with fire‐prone ecosystems, namely SW Cape (South Africa), SW Australia, California and the Mediterranean Basin (Andalusia, Spain). Methods Using long‐term monthly rainfall data from stations dispersed across the four regions, we computed monthly means and interannual variation for each month of the year — the latter quantified as the coefficient of variation (CV) — and divided these into winter and summer seasons. We also computed the mean number of rainfall events, the mean frequency in various categories of event duration (days), the amount of rainfall per event (mm) and the rainfall intensity per event (mm/day) per year for winter and summer seasons for a subset of the rainfall stations. Results The fraction of rain falling in summer was lowest in California (5%) and similarly low (c. 25%) in the other three regions. The hierarchy of values of coefficient of variation (CV) of monthly rainfall during the winter period was as follows: California > Andalusia >> SW Cape > SW Australia; results for summer were: California > > Andalusia >> SW Australia ～ SW Cape. SW Australian sites experienced the greatest frequency of short, small and low‐intensity rainfall events in both seasons; patterns in the SW Cape were intermediate between Australia and the two northern hemisphere sites which both received fewer, larger and more intense events. Overall, the two southern hemisphere regions (SW Australia and the SW Cape) had significantly more reliable regimes than the two northern hemisphere ones (Mediterranean Basin and California). Main conclusions These differences in rainfall reliability regimes may provide a novel perspective on the distribution of certain plant life‐history traits in mediterranean‐climate ecosystems. Less reliable regimes would select for germination and seedling survival traits that enable persistence of genets in the face of uncertain moisture conditions during the winter and spring establishment phase. Study systems that accommodate for phylogenetic constraints, namely invasive species derived from mediterranean‐climate ecosystems, as well as shared lineages, provide good opportunities to develop and test hypotheses on the implication of different rainfall reliability regimes. One of the novel implications of this study is that the distinctive trait of assemblages in the southern hemisphere regions may be a consequence not so much of their shared nutrient‐poor soils as of their similarly reliable rainfall regimes.     

Light Dependence of Chloroplast Replication and Starch Metabolism in the Moss Polytrichum commune

Spores of Polytrichum conwtuine were grown on a mineral salt solution with or without sucrose and exposed to continuous white light, continuous darkness, red light and/or far-red light. With sucrose, germination and filament growth occurred in all conditions, Without sucrose, germination and filament growth occurred only in light. Two phytochrome mediated responses of the chloroplasts were demonstrated. Chloroplast replication occurred in continuous white light and red light of 15 min/6 hours. In continuous darkness and in far red light of 15 min/6 hours, the size of the chloroplasts increased; but no replication occurred. Both the chloroplast replication and chloroplast size were red, far-red light reversible. When changed from one continuous light environment to another, a lag period occurred before the chloroplasts responded to the new environment. Electron micrographs of sections and in vivo staining of the chloroplasts with iodine solution demonstrated that the change in size of the chloroplasts was at least partially due to the synthesis and degradation of starch.     

A novel approach to the generation of high affinity class II-binding peptides

We have found that if core regions crucial for class II binding are incorporated in multiple copies in the same peptide molecule ("reiterative motifs"), marked enhancement of the binding capacity occurs. Isotype specificity (IAd vs IEd binding capacities) is retained in all three antigenic determinants so far analyzed (lambda rep 12-26, OVA 323-339, and hen egg lysozyme 105-120). The mechanism involved in such an effect is not clear, but experiments involving introduction of a peptide spacer between two repeated core regions do not support the notion that the effect is mediated by cross-linking of more than one MHC molecule, favoring the possibility that conformational effects or distinct subsites of interaction on the MHC molecule may be involved. Based on reiterative structures, a peptide molecule composed of only two different amino acids (Ala and His) has been produced that still retains a very high binding affinity. An 125I-radiolabeled form of this peptide has been used to demonstrate that the high binding detected is mediated by the same binding site involved in the interaction of IAd and OVA 323-339. Inhibition of Ag presentation studies further supports the immunologic relevance of the phenomena observed. Finally, we observed naturally occurring clustered binding sites in proximity of immunodominant protein regions, raising the possibility that the phenomenon might have a physiologic counterpart.     

Comparison of two host cell range variants of feline immunodeficiency virus.

Two molecular clones of feline immunodeficiency virus were compared. The first clone, 34TF10, was from a Petaluma, Calif., isolate; the second, PPR, was isolated from a cat in the San Diego, Calif., area. The cats from which the isolates were obtained suffered from chronic debilitating illnesses. The two molecular clones differed in their in vitro host cell range. The 34TF10 clone infected the Crandall feline kidney and G355-5 cell lines, but replicated less efficiently on feline peripheral blood leukocytes. In contrast, the PPR clone productively infected the primary feline peripheral blood leukocytes but not Crandall feline kidney or G355-5 cells. The 34TF10 and PPR clones had an overall sequence identity of 91%. The env gene was the least conserved (85% at the amino acid level). Additionally, the potential open reading frame for a Tat-like protein, ORF 2, contained a stop codon in the 34TF10 isolate which was not found in the PPR clone. This truncation did not prevent in vitro or in vivo replication of 34TF10. Two splice acceptor sites were identified in the 34TF10 clone. One was 5' to the beginning of the putative tat open reading frame, and the other was 5' to the putative vif product. Both of these acceptor sites were conserved in the PPR clone. The long terminal repeats of the viruses were 7% divergent between the two clones, with a lack of conservation in putative NF-kappa B, LBP-1, and CCAAT enhancer-promoter sites.     

Absence of nitrogen fixation (acetylene reduction) by procaryotes in nectar of Banksias

Summary An earlier hypothesis that blue-green algae in the nectar ofBanksia telmatiaea contribute to the nitrogen economy of the host by fixing N₂ was tested. Field and laboratory experiments failed to demonstrate C₂H₄ production in C₂H₂-treated containers over extended periods. Soil N was not higher at the end of the flowering season and plants in which flower heads were removed prior to nectar production did not contain less N than the controls.     

TISSUE LONGEVITY OF THE ARBORESCENT MONOCOTYLEDON,KINGIA AUSTRALIS (XANTHORRHOEACEAE)

Histochemical tests for tissue viability and microscopic examination of stem fragments of known age showed that the pith parenchyma of Kingia australis may survive for over 400 years. The longevity of phloem appears much lower, but ³²P translocation studies indicate that this may still exceed 100 years. Explanations for such extreme longevity of adult tissue are suggested.     

Inhibition of experimental autoimmune encephalomyelitis induction in SJL/J mice by using a peptide with high affinity for IAs molecules.

Blocking of the Ag presenting function of MHC by peptides capable of high affinity binding to this molecule has been proposed as a potential immunotherapeutic intervention in MHC-associated diseases. Recent studies have used this strategy to prevent the induction of experimental allergic encephalomyelitis (EAE) in mice. However, because of the close structural relationship between the inhibitor and encephalitogenic peptides, the results of these previous studies have been difficult to interpret with regard to whether MHC blockade was the mechanism by which the inhibitory peptides functioned. In our study, we have determined the capacity of unrelated peptides capable of binding with high affinity to IAs in inhibiting the induction of EAE in SJL/J mice after immunization with the autoantigenic peptide PLP 139-151. Prevention of the disease was accomplished by two methods: 1) when inhibitor was administered together with the encephalitogenic peptide at the time of immunization, as in previous studies, and 2) when inhibitor was administered at a separate site from the autoantigen 1 day before the immunization with that Ag. Inhibition was due to binding of the inhibitor to IAs, as evidenced by the fact that a control peptide incapable of binding to this MHC had no effect on the course of the disease. The finding that inhibitor could also be efficacious when administered at a separate site has implications for potential use of such a strategy to reverse ongoing autoimmune diseases. The inhibitor had to be present during the time of Ag stimulation, and had no long term inhibitory effects, in that a secondary immune response to the encephalitogenic peptide was not inhibited in animals given the inhibitory peptide before the induction of a primary response. This is compatible with the conclusion that MHC blockade was, in fact, the mechanism of the inhibition, rather than as a result of any long term suppressive effects on immunoreactive T cells. Finally, not only did administration of the inhibitory peptide lead to a prevention of the induction of EAE, but it could also be shown to decrease the T cell proliferative response in vitro to the autoantigen.     

GENETIC SUBSTRUCTURE OF THE PACIFIC HARBOR SEAL (PHOCA VITULINA RICHARDSI) OFF WASHINGTON, OREGON, AND CALIFORNIA

Genetic substructure among groups of Pacific harbor seals, Phoca vitulina richardsi , along the western coast of the United States was investigated using mitochondrial DNA sequences. Blood and tissue samples were removed from 86 seals inhabiting Puget Sound and the Pacific coasts of Washington, Oregon, and California. A 320 base-pair segment of the control region was amplified using the polymerase chain reaction and directly sequenced. These data indicated a high level of diversity. Thirty variable sites were found that define 47 mitochondrial haplotypes. Among groups of P. v. richardsi sampled, 5 haplotypes were shared, but most (42) were unique to a locality. Haplotypic frequency and an Analysis of Molecular Variance (A mova ) revealed significant differences ( P = 0.001) among regions. Phylogenetic analysis indicated Puget Sound seals possess unique divergent lineages not found in seals from the coasts of Washington, Oregon, and California. These lineages may represent haplotypes from north of Washington, which is consistent with late reproductive timing of harbor seals from Puget Sound.