Browsing by Author "Algar, Natalie"

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    Determinants of gemmae output in the liverwort Lophozia ventricosa
    (2004) Algar, Natalie; Söderström, Lars; Hedderson, Terry A
    The spacial variation and population parameters affecting gemmae output of a boreal and arctic liverwort species, Lophozia ventricosa, were studied in Trnndelag, a boreal region of central Norway and in the arctic tundra on Svalbard. The population parameters investigated included colony size, colony shoot density, number of gemmae per shoot, proportion of gemmiferous shoots and gemmiferous shoot density. The gemmae output in a colony was calculated as the product of the number of gemmae per shoot, colony size and gemmifeorus shoot density. A Nested Analysis of Variance was used to partition population parameters spacially and a Pearsons Product-Moment Correlation was used to evaluate which of these population parameters affect gemmae output in a colony. The number of gemmae per shoot differed significantly between areas, populations and colonies, and was significantly varied between populations and colonies on Svalbard. No significant variation in the number of gemmae per shoot was found in Trnndelag. Population influences on shoot density, gemmiferous shoot density and gemmae output were significant in Trnndelag. This was expected, as more shoots in a colony is thought to influence gemmiferous shoot density and gemmae output. In Trnndelag, the only significant relation that can explain gemmae output is colony size whereas on Svalbard, gemmae output in a colony is affected by colony size, shoot density and number of gemmae per shoot. The results indicate that most of the variation in gemmae output occurs at the population level and that gemmae output differs between the arctic and boreal regions.
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    Stretched to the limit : leaf tensile properties and lignin content of resurrection plants
    (2004) Algar, Natalie; Farrant, Jill M; Vander Willigen, Clare
    Leaf tensile strength was measured for four resurrection plants, Craterostigma wilmsii Engl, Xerophyta schlecteri (Baker) N.L. Menezes, Xerophyta humilis (Baker) T. Durand & Schinz and Sporobolus stapfianus Gandoger, as well as two desiccation-sensitive controls, Zea mays L. and Arabidopsis thaliana (L.) Heynh. (ecotype Columbia) at full hydration and after dehydration, both on the plant (naturally-dried) and rapidly off the plant causing death (flash-dried). In the desiccation-tolerant plants, leaf tensile strength was higher in the monocots than the dicots at full hydration. Three different mechanisms of cell protection occur in resurrection plants on drying: cell-wall folding, packing vacuoles with non-aqueous solute or a combination of the two. Tensile strength in C. wilmsii ( dicot) increased when naturally-dried but decreased when flash-dried, possibly due to the nature of the drying mechanisms (wall folding). The, leaf tensile strength of the Xerophyte species, both monocots, increased when naturally dried and when flashdried. Xerophyte species pack their vacuoles during desiccation. S. stapfianus, a grass which uses a combination of wall folding and vacuole packing, had the highest tensile strength possibly due to its unique architectural structure. Differences in leaf architecture, in terms of lignin content, were examined using light microscopy after histo-chemical staining for lignin, which showed that monocotyledons had a higher percentage of lignin per unit leaf cross-sectional area than dicotyledons. A regression analysis revealed that leaf tensile strength and lignin content were positively correlated in fully hydrated leaves I but no relationship existed between lignin content and naturally dried leaves. This may be due to variations of protective mechanisms induced during desiccation by the four resurrection plants. Notching was observed in X schlechteri, behaving differently to grasses which are notch-insensitive, possibly due to large lignin contents on the outer edges of the leaves.