A.P. van Beem

Flavonoid concentrations in three grass species and a sedge grown in the field and under controlled environment conditions in response to enhanced UV-B radiation.

An investigation was carried out to find whether enhanced levels of UV-B radiation induce increased concentrations of flavonoids in the leaves of the grass species Deschampsia antarctica, Deschampsia borealis and Calamagrostis epigeios and the sedge Carex arenaria. Whether the enhanced levels of UV-B influenced the proportions of the various flavonoids in the leaves was also studied. Increased flavonoid concentrations would improve the UV-B shielding of UV-B susceptible tissues. Using HPLC analysis the flavonoids orientin and luteolin were identified in D. antarctica, orientin in D. borealis and tricin in C. arenaria. Neither flavonoid concentrations nor the proportion of the various flavonoids in climate room grown D. antarctica and D. borealis plants differed between individuals grown under 0, ambient or elevated UV-B levels. After 12 weeks of growth biomass production and shoot-to-root ratios of D. antarctica were not affected by elevated UV-B radiation. Greenhouse grown C. epigeios plants contained higher concentrations and different proportions of flavonoids grown under elevated levels of UV-B than when grown under ambient or 0 UV-B. In C. epigeios plants grown in their natural habitat in the field under ambient or elevated levels of UV-B, flavonoid concentrations and proportions were the same in plants from both treatments. In the leaves of the sedge C. arenaria grown in a greenhouse flavonoid concentrations and proportions were not affected by UV-B radiation. Leaves were harvested four times during the growing season from C. arenaria plants grown in their natural habitat in the field under ambient or elevated levels of UV-B. Leaves harvested in January contained higher concentrations of flavonoids when grown under elevated UV-B than when grown under ambient UV-B radiation. In leaves harvested in May, September and December flavonoid concentrations were the same in plants grown under ambient or elevated UV-B. The proportion of the different flavonoids was the same for both treatments in all months. These results indicate that constitutive levels of flavonoids in these grass and sedge species are adequately high to protect them against ambient and elevated levels of solar UV-B radiation.

Increased solar UV-B radiation may reduce infection by arbuscular mycorrhizal fungi (AMF) in dune grassland plants: evidence from five years of field exposure

An area of coastal dune grassland, dominated by the gramineous species Calamagrostis epigeios and Carex arenaria, was exposed to enhanced levels of UV-B radiation during a five year period. These species showed reduced AM-fungal infection percentages in their roots. In C. epigeios AM infection was reduced by 18%, C. arenaria showed a reduction by 20%. The major effect of enhanced UV-B on AM associations was a reduction of the number of arbuscules. This indicates a reduction in the exchange of nutrients between the symbionts. Since the effect of UV-B on AM associations may result from altered flavonoid levels in the root exudates of the host plants, flavonoid levels in the roots were investigated. No detectable flavonoid concentrations were found in the roots of C. epigeios and C. arenaria. Less effective AM associations can have pronounced negative effects on biodiversity and nutrient dynamics of the dune grassland ecosystem. The possible mechanisms causing these indirect effects of elevated UV-B on below ground AM associations are discussed. We conclude that UV-B induced changes in plant hormone levels are more likely to be the mechanism reducing AMF infection than UV-B induced alterations in flavonoid concentrations in the root exudates of the host plant.

(Poly)phenolic compounds in pollen and spores of Antarctic plants as indicators of solar UV-B

The morphology, size and characteristics of the pollen of the plant species Antarctic hairgrass (Deschampsia antarctica, Poaceae) and Antarctic pearlwort (Colobanthus quitensis, Caryophyllaceae) are described by scanning electron microscopy and light microscopy. Based on the number of pores the pollen of Colobanthus quitensis is classified as periporate or polypantorate, while that of Deschampsia antarctica is monoporate.

Growth and morphology of Draparnaldia mutabilis (Chlorophyceae, Chaetophorales) in synthetic medium

The development and morphology of Draparnaldia mutabilis under various culture conditions is described. The germination of zoospores is strictly erect. In the first stage of development a primary rhizoid or a small prostrate system is formed, which is generally replaced in a later stage by persistent secondary rhizoids originating from basal cells of the main axis. Optimal growth occurs at about 20°C and at relatively high light intensities. The phenotypic appearance found in field material is maintained best in culture in a dilute modified Woods Hole medium at 8°C under short day conditions. In more nutrient-rich media the typical features of Draparnaldia, especially differentiation of main axes and lateral fascicles, disappear and the plants attain a Stigeoclonium-like habit. Morphological variation has been studied in herbarium material and freshly collected specimens from several localities in The Netherlands. Evidence is presented that in The Netherlands only one, rather polymorphic Draparnaldia spec...