Chemical Composition of Bleeding Xylem Sap from Kiwifruit Vines

A study of the chemical composition and charge balance was madeof bleeding xylem sap collected from excised one-year-old extensionshoots of healthy, Mn-deficient, Mn-toxic and Zn-deficient kiwifruitvines (Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson)immediately prior to leafburst. The exudates were analysed formacronutrient cations and anions, trace elements, amino acids,organic acids and sugars. Major charged species measured wereCa (13.3 mM), K (8.9 mM), Mg (5.6 mM), malate (12.5 mM) andphosphate (5.8 mM). Glutamine (12 mM) was the predominant Ncarrier identified, accounting for 58 per cent of the totalN followed by NO₂^–-N (4.5 per cent), NH₄⁺-N (3.5 per cent)and arginine-N (2.9 per cent). Approximately 22 per cent ofthe N was in a hydrolysable proteinaceous fraction comprisingmainly glutamine and glutamate. Eighteen free proteinaceousamino acids were idetified in sap, the most abundant being glutamine,glutamic acid, valine, isoleucine and phenylalanine. Computersimulation of the chemical composition predicted that in additionto hydrated cations, ion pairs formed between inorganic components(SO₄^2–, HPO₄^2–, H₂PO₄^–) and cations (Ca²⁺,Mg²⁺, Mn²⁺), plus metal-organic ligand complexes (Ca Malate,Zn Malate, FeCit, CuHis, CuGln) are important species involvedin translocation. The solubility product of hydroxyapatite wasexceeded in all exudates although in vitro precipitation wasnot observed. To achieve electroneutrality with the componentsmeasured, however, formation of precipitate precursors (hydroxyapatitenuclei) had to be assumed. Irregularities in Mn nutrition (butnot Zn) were clearly indicated by the elemental compositionof exudate suggesting the use of sap analysis as a possiblepre-season indicator of nutritional status for this species. Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson, kiwifruit, xylem sap composition, trace metals, amino acids, organic acids     

Amphioxus and the Utility of Molecular Genetic Data for Hypothesizing Body Part Homologies between Distantly Related Animals

Expression domains of developmental genes can indicate bodypart homologies between distantly related animals and give insightsinto interesting evolutionary questions. Two of the chief criteriafor recognizing homologies are relative position with respectto surrounding body parts and special quality (for instance,a vertebrate testis, regardless of its location, is recognizableby its seminiferous cysts or tubules). When overall body plansof two animals are relatively similar, as for amphioxus versusvertebrates, body part homologies can be supported by developmentalgene expression domains, which have properties of special qualityand relative position. With expression patterns of AmphiNk2-land AmphiPax2/5/8, we reexamine the proposed homology betweenthe amphioxus endostyle and the vertebrate thyroid gland, anda previously good homology is made better. When body plans ofanimals are disparate, body part homologies supported by moleculargenetic data are less convincing, because the criterion of relativeposition of gene expression domains becomes uncertain. Thus,when expression of amphioxus AmphiBMP2/4 is used to comparethe dorsoventral axis between amphioxus and other animals, acomparison between amphioxus and vertebrates is more convincingthan comparison between amphioxus and other invertebrates withdisparate body plans. In spite of this difficulty, the use ofdevelopmental genetic evidence comparing animals with disparatebody plans is currently putting the big picture of evolutioninto new perspective. For example, some molecular geneticistsare now suggesting that the last common ancestor of all bilateriananimals might have been more annelid-like than flatworm-like.     

Recolonization of forest fragments by a native rodent following experimental ‘extinctions’

The movement of organisms between subdivided populations is considered a key influence on the persistence of species in modified landscapes. In particular, the ability to recolonize ‘empty’ fragments of habitat is directly relevant to conservation management, and to understanding the link between pattern and process in metapopulations. We studied the movement and recolonization ability of the bush rat, Rattus fuscipes, in a highly fragmented agricultural landscape in south‐western Victoria, Australia. Populations were monitored in seven small (<2.5 ha) and two large (>49 ha) forest fragments before removal of all residents from four of the small fragments. Subsequent monitoring (for up to 16 months) allowed the detection of colonizing individuals, and comparisons between ‘experimental’ and ‘control’ fragments. Rattus fuscipes readily moved between fragments and successfully recolonized (i.e. both males and females arrived) two of four fragments in which extinctions were simulated. A single male moved into a third experimental fragment. In one fragment, new animals were detected 1 month after the removal of residents, indicating that recolonization can occur rapidly. Dispersers were not a random sample of the population: although both males and females, and adults and sub‐adults were recorded dispersing, adult males in reproductive condition predominated. Functional connectivity appears to be high for R. fuscipes in the study landscape. Results from this manipulative experiment provide direct empirical evidence that a capacity for movement allows recolonization of fragments of suitable habitat and is a key process responsible for species persistence in fragmented landscapes, as predicted by theory.