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1.  Is leaf dry matter content a better predictor of soil fertility than specific leaf area? 
Annals of Botany  2011;108(7):1337-1345.
Background and Aims
Specific leaf area (SLA), a key element of the ‘worldwide leaf economics spectrum’, is the preferred ‘soft’ plant trait for assessing soil fertility. SLA is a function of leaf dry matter content (LDMC) and leaf thickness (LT). The first, LDMC, defines leaf construction costs and can be used instead of SLA. However, LT identifies shade at its lowest extreme and succulence at its highest, and is not related to soil fertility. Why then is SLA more frequently used as a predictor of soil fertility than LDMC?
SLA, LDMC and LT were measured and leaf density (LD) estimated for almost 2000 species, and the capacity of LD to predict LDMC was examined, as was the relative contribution of LDMC and LT to the expression of SLA. Subsequently, the relationships between SLA, LDMC and LT with respect to soil fertility and shade were described.
Key Results
Although LD is strongly related to LDMC, and LDMC and LT each contribute equally to the expression of SLA, the exact relationships differ between ecological groupings. LDMC predicts leaf nitrogen content and soil fertility but, because LT primarily varies with light intensity, SLA increases in response to both increased shade and increased fertility.
Gradients of soil fertility are frequently also gradients of biomass accumulation with reduced irradiance lower in the canopy. Therefore, SLA, which includes both fertility and shade components, may often discriminate better between communities or treatments than LDMC. However, LDMC should always be the preferred trait for assessing gradients of soil fertility uncoupled from shade. Nevertheless, because leaves multitask, individual leaf traits do not necessarily exhibit exact functional equivalence between species. In consequence, rather than using a single stand-alone predictor, multivariate analyses using several leaf traits is recommended.
PMCID: PMC3197453  PMID: 21948627
Ellenberg numbers; functional traits; leaf density; leaf nitrogen; leaf size; leaf thickness; relative growth rate (RGR); shade tolerance; variation in trait expression
2.  Stomatal vs. genome size in angiosperms: the somatic tail wagging the genomic dog? 
Annals of Botany  2010;105(4):573-584.
Background and Aims
Genome size is a function, and the product, of cell volume. As such it is contingent on ecological circumstance. The nature of ‘this ecological circumstance’ is, however, hotly debated. Here, we investigate for angiosperms whether stomatal size may be this ‘missing link’: the primary determinant of genome size. Stomata are crucial for photosynthesis and their size affects functional efficiency.
Stomatal and leaf characteristics were measured for 1442 species from Argentina, Iran, Spain and the UK and, using PCA, some emergent ecological and taxonomic patterns identified. Subsequently, an assessment of the relationship between genome-size values obtained from the Plant DNA C-values database and measurements of stomatal size was carried out.
Key Results
Stomatal size is an ecologically important attribute. It varies with life-history (woody species < herbaceous species < vernal geophytes) and contributes to ecologically and physiologically important axes of leaf specialization. Moreover, it is positively correlated with genome size across a wide range of major taxa.
Stomatal size predicts genome size within angiosperms. Correlation is not, however, proof of causality and here our interpretation is hampered by unexpected deficiencies in the scientific literature. Firstly, there are discrepancies between our own observations and established ideas about the ecological significance of stomatal size; very large stomata, theoretically facilitating photosynthesis in deep shade, were, in this study (and in other studies), primarily associated with vernal geophytes of unshaded habitats. Secondly, the lower size limit at which stomata can function efficiently, and the ecological circumstances under which these minute stomata might occur, have not been satisfactorally resolved. Thus, our hypothesis, that the optimization of stomatal size for functional efficiency is a major ecological determinant of genome size, remains unproven.
PMCID: PMC2850795  PMID: 20375204
Stomatal size; genome size; seed size; life history; photosynthesis; allometry; ecology; evolution; SLA; leaf structure; CAM; C4
3.  Cloning and characterization of transcripts showing virulence-related gene expression in Naegleria fowleri. 
Infection and Immunity  1992;60(6):2418-2424.
The pathogenic LEE strain of Naegleria fowleri isolated from human or mouse brain loses pathogenicity when cultured axenically in a nutrient broth. To identify genes differentially expressed in highly virulent versus weakly virulent amoebae, a cDNA library was constructed by using mRNA from amoebae recovered from a mouse brain. Two cDNA clones were isolated by differential screening of the library. The transcript homologous to clone Nf314 was preferentially expressed in highly virulent cells, whereas the transcript homologous to clone Nf435 was preferentially expressed in weakly virulent cells. Other clones showed negligible differential hybridization, but actin transcript levels were slightly elevated in the highly virulent cells. The Nf314 cDNA has an open reading frame for a 53-kDa protein 94% similar and 19% identical over 194 amino acid residues to serine carboxypeptidase from yeast cells, barley, and wheat. Southern blot analysis is consistent with a single copy of the Nf314 gene in the genome. Interestingly, the increased Nf314 transcript levels were present in cells fed on mouse brain, liver, or NIH 3T3 fibroblasts but not in cells fed on bacteria or in axenic culture. Thus, the inducer of the increased gene expression correlates with use of mammalian cells as a food source without regard to level of virulence. Since amoebae fed in culture on dissociated mouse brain were weakly virulent, as measured by their abilities to kill mice, the Nf314 gene may be required but is not sufficient for increased virulence.
PMCID: PMC257175  PMID: 1587609
4.  Virulence-related protein synthesis in Naegleria fowleri. 
Infection and Immunity  1991;59(11):4278-4282.
Protein synthesis patterns of the low-virulence Naegleria fowleri LEE strain from axenic culture, the same strain after mouse brain passage to increase virulence, and the same strain after growth on bacteria were studied. Comparisons of accumulated proteins, in vivo-synthesized proteins, and in vitro-synthesized proteins translated from poly(A)+ mRNA were made. Differences between amoebae from the different treatments were noted. After 6 months in axenic culture, pathogenic protein synthesis patterns were lost and there was a decrease in virulence. Therefore, the increase in virulence is correlated with numerous specific changes in protein synthesis.
PMCID: PMC259031  PMID: 1937787
5.  Hemin Replaces Serum as a Growth Requirement for Naegleria 
Applied Microbiology  1974;28(1):64-65.
Four strains of Naegleria gruberi were grown axenically without serum. Serum was replaced by hemin or two selected hemoproteins. Aside from the utility of eliminating serum from the culture medium, the present work shows that Naegleria does not require intact protein, and establishes a specific micronutrient requirement for this amoebo-flagellate.
PMCID: PMC186590  PMID: 4844269
The Journal of Cell Biology  1971;50(3):634-651.
The membranes of Acanthamoeba palestinensis were studied by examination in fixed cells, and then by following the movements of glycerol-3H-labeled phospholipids by cell fractionation. Two previously undescribed structures were observed: collapsed cytoplasmic vesicles of cup shape, and plaques in food vacuole and plasma membrane similar in size to the collapsed vesicles. It appeared that the plaques formed by insertion of collapsed vesicles into membranes and/or that collapsed vesicles formed by pinching off of plaques. Fractions were isolated, enriched with nuclei, rough endoplasmic reticulum (RER), plasma membrane, Golgi-like membranes, and collapsed vesicles. The changes in specific activity of glycerol-3H-labeled phospholipids in these membranes during incorporation, turnover, and after pulse-labeling indicated an ordered sequence of appearances of newly synthesized phospholipids, first in nuclei and RER, then successively in Golgi membranes, collapsed vesicles, and finally, plasma membrane. In previous work we had found no large nonmembranous phospholipid pool in A. palestinensis. These observations are consistent with the hypothesis that membrane phospholipids are synthesized, perhaps as integral parts of membranes, in RER and nuclei. Subsequently, some of the newly synthesized phospholipids are transported to the Golgi complex to become integrated into the membranes of collapsed vesicles, which are precursors of the plasma membrane. Collapsed vesicles from the plasma membrane by inserting into it as plaques. When portions of the plasmalemma from food vacuoles, collapsed vesicles pinch off from their membranes and are recycled back to the cell surface.
PMCID: PMC2108308  PMID: 4329152
The Journal of Cell Biology  1971;50(3):625-633.
In order to determine the feasibility of using radioactive precursors as markers for membrane phospholipids in Acanthamoeba palestinensis, the characteristics of phospholipids labeled with choline-14C and glycerol-3H were examined. Choline-14C was found to be a specific label for phosphatidyl choline. There was a turnover of the radioactive moiety of phosphatidyl choline at a rate that varied with the concentration of nonradioactive choline added to the growth medium. Radioactivity was lost from labeled phosphatidyl choline into the acid-soluble intracellular pool and from the pool into the extracellular medium. This loss of radioactivity from cells leveled off and an equilibrium was reached between the label in the cells and in the medium. Radioactive choline was incorporated into phosphatidyl choline by cell-free microsomal suspensions. This incorporation leveled off with the attainment of an equilibrium between the choline-14C in the reaction mixture and the choline-14C moiety of phosphatidyl choline in the microsomal membranes. Therefore, a choline exchange reaction may occur in cell-free membranes, as well as living A. palestinensis. In contrast to choline-14C, the apparent turnover of glycerol-3H-labeled phospholipids was not affected by large concentrations of nonradioactive choline or glycerol in the medium. The radioactivity in lipids labeled with glycerol-3H consisted of 33% neutral lipids and 67% phospholipids. Phospholipids labeled with glycerol-3H turned over slowly, with a concomitant increase in the percentage of label in neutral lipids, indicating a conversion of phospholipids to neutral lipids. Because most (∼96%) of the glycerol-3H recovered from microsomal membranes was in phospholipids, whereas only a minor component (∼2%) of the glycerol-3H was in the phospholipids isolated from nonmembrane lipids, glycerol-3H was judged to be a specific marker for membrane phospholipids.
PMCID: PMC2108296  PMID: 5098863

Results 1-7 (7)