Acclimation of Trees to Pollution Stress: Cellular Metal Tolerance Traits

Cell suspension cultures were established from shoot explantsof mature trees of Acer pseudoplatanus L. (sycamore) at a sitecontaminated by aerial deposition of copper and cadmium frommetal processing industry, and from the same species at uncontaminatedsites. The responses of cell cultures to elevated metal concentrationsin growth media differed markedly according to site of origin.Both Cu and Cd, applied singly at concentrations of 10–15mg l^–1, inhibited growth and were toxic to cultures originatingfrom the uncontaminated sites, but not to cultures from thecontaminated site. This metal tolerance trait in the culturesfrom the contaminated site was stable through repeated sub-culturing.It could also be induced in one culture originating from thereference uncontaminated site, by gradually exposing the cultureto increasing concentrations of Cu. A reduced level of metalremoval from the media was found in tolerant cultures, comparedto non-tolerant cultures. The results of these experiments demonstratethe occurrence of an alteration of gene expression in responseto pollution stress, suggesting that metal tolerance may beinduced within shoot meristems in vivo. It also represents thefirst example of non-mycorrhizal adaptation to metal toxicityidentified in woody plants. Trees, pollution, metal tolerance, acclimation, plant tissue culture, Acer pseudoplaianus L., sycamore     

Heterophylly in Ranunculus flabellaris: The Effect of Abscisic Acid on Leaf Ultrastructure

Ranunculus flabellaris Rafin., an aquatic buttercup, exhibitsheterophylly at the level of cellular ultrastructure. Comparedto terrestrial leaves, underwater leaves have thinner epidermalcell walls and more numerous paramural bodies per epidermaland mesophyll cell cross-section. The number of chloroplastsand mitochondria in cell cross-sections also contrasts betweenthe two leaf types. Despite within-and between-leaf variations,different patterns of organelle distribution for the two leafforms were found using principal coordinates analysis. In addition,underwater leaf chloroplasts are smaller, have fewer grana,a greater number of thylakoids/granum, and less starch comparedto chloroplasts from terrestrial leaves. At the ultrastructurallevel, submergence in ABA solution does not produce a leaf withas many characteristics of the terrestrial environment, as shownin previous studies of leaf morphology and anatomy. While numberand distribution of organelles in ABA-treated leaves are similarto terrestrial leaves, some features of chloroplast internalstructure and paramural body number and distribution resembleunderwater leaves. It is postulated that ABA acts as a morphogeninvolved in guiding the irreversible processes of leaf development,but certain subcellular characteristics may be determined directlyby the physical environment. Difficulties encountered in quantitativeanalyses of cellular ultrastructure are discussed. Ranunculus flabellaris, ABA, heterophylly, leaf ultrastructure, principal coordinates analysis     

Modification of the Pollen-Stigma Interaction in Brassica oleracea by Water

The presence of a film of distilled water on the stigma surfaceof freshly opened flowers results in complete inhibition ofpollen following both incompatible and compatible pollinationsin self-incompatible (SI) genotypes of Brassica oleracea, SIgenotypes of B. campestris and one self-compatible (SC) genotypeof B. campestris. The application of water to the stigmas afterpollination also resulted in a marked reduction in pollen germinationand tube penetration. An increase in the time intervals betweenthe application of pollen onto the stigma and the water treatmentprogressively reduced this inhibition. Pollen germination wasalso completely inhibited when stigmas from freshly-opened flowersof SI B. campestris and B. oleracea genotypes were washed inwater, dried and pollinated with pollen grains of either compatibility.The ability of stigmas to induce pollen germination and tubegrowth was restored over a period, the length of which was dependenton the incompatibility (S) genotype. Stigmas of B. napus (SC)and SC mutants of SI B. campestris were found to be affectedby washing, but stigmas of a SC variety of B. campestris andthe immature stigmas from buds of B. oleracea were found tobe considerably less affected. Microscopic examination of pollenplaced on washed stigmas reveals that grains, irrespective oftheir compatibility, fail to hydrate normally. When inducedto hydrate by raising atmospheric humidity, pollen grains onwashed stigmas did germinate, but most of the tubes failed topenetrate the papillar wall and very few entered the style.It is proposed that the water treatment mobilises componentsof the pellicle which reorganize to block the activity of molecules,present in both SC and SI individuals, responsible for establishingfull contact between the pellicle and pollen grain coating. Brassica, pellicle, pollen, recognition, self-incompatibility     

Functional and performance comparisons of invasive Hieracium lepidulum and co‐occurring species in New Zealand

Abstract One of the key environmental factors affecting plant species abundance, including that of invasive exotics, is nutrient resource availability. Plant functional response to nutrient availability, and what this tells us about plant interactions with associated species, may therefore give us clues about underlying processes related to plant abundance and invasion. Patterns of abundance of Hieracium lepidulum, a European herbaceous invader of subalpine New Zealand, appear to be related to soil fertility/nutrient availability, however, abundance may be influenced by other factors including disturbance. In this study we compare H. lepidulum and field co‐occurring species for growth performance across artificial nutrient concentration gradients, for relative competitiveness and for response to disturbance, to construct a functional profile of the species. Hieracium lepidulum was found to be significantly different in its functional response to nutrient concentration gradients. Hieracium lepidulum had high relative growth rate, high yield and root plasticity in response to nutrient concentration dilution, relatively low absolute yield, low competitive yield and a positive response to clipping disturbance relative to other species. Based on overall functional response to nutrient concentration gradients, compared with other species found at the same field sites, we hypothesize that H. lepidulum invasion is not related to competitive domination. Relatively low tolerance of nutrient dilution leads us to predict that H. lepidulum is likely to be restricted from invading low fertility sites, including sites within alpine vegetation or where intact high biomass plant communities are found. Positive response to clipping disturbance and relatively high nutrient requirement, despite poor competitive performance, leads us to predict that H. lepidulum may respond to selective grazing disturbance of associated vegetation. These results are discussed in relation to published observations of H. lepidulum in New Zealand and possible tests for the hypotheses raised here.     

The behaviour of Bretnia lactucae on cultivars of Lactuca sativa and on other composites

The spores of an isolate of Bremia lactucae obtained from lettuce germinated equally well on Cellophane and on the surfaces of all plant species inoculated. The fungus penetrated the epidermal cells of both host and non-host plants but extensively invaded only certain lettuce cultivars. Many of the species and cultivars inoculated showed no macroscopic symptoms but exhibited a hypersensitive response to invasion that was limited to a few cells and only visible microscopically. However, the hypersensitive response was not always so limited and in some species, fungal development and associated host cell necrosis was more extensive and visible macroscopically. In such instances, limited sporulation occasionally occurred. On some lettuce cultivars symptoms developed more slowly than on fully susceptible ones and less seedlings became diseased. This was due to the heterogeneity of the inoculum with respect to its ability to overcome certain race specific resistance genes. Such cultivars reacted hypersensitively to the majority, but not all, of the fungal propagules applied and the observed effect was thus due to a lower effective inoculum concentration. Without due care, both these types of ‘intermediate’ reaction could easily be misinterpreted as race non-specific resistance particularly under field conditions. These observations emphasized the problems of categorizing cultivars and species rigidly as resistant or susceptible when inoculum could be heterogenous or when resistance reactions allowed some macroscopic symptom development.