Factors affecting levels of some phenolic compounds, digestibility, and nitrogen content of the mature leaves ofBarteria fistulosa (Passifloraceae)

Sand supplementation favors tropical seagrass Thalassia hemprichii in eutrophic bay: implications for seagrass restoration and management

BACKGROUND

Sediment is crucial for the unique marine angiosperm seagrass growth and successful restoration. Sediment modification induced by eutrophication also exacerbates seagrass decline and reduces plantation and transplantation survival rates. However, we lack information regarding the influence of sediment on seagrass photosynthesis and the metabolics, especially regarding the key secondary metabolic flavone. Meanwhile, sulfation of flavonoids in seagrass may mitigate sulfide intrusion, but limited evidence is available.

RESULTS

We cultured the seagrass Thalassia hemprichii under controlled laboratory conditions in three sediment types by combining different ratios of in-situ eutrophic sediment and coarse beach sand. We examined the effects of beach sand mixed with natural eutrophic sediments on seagrass using photobiology, metabolomics and isotope labelling approaches. Seagrasses grown in eutrophic sediments mixed with beach sand exhibited significantly higher photosynthetic activity, with a larger relative maximum electron transport rate and minimum saturating irradiance. Simultaneously, considerably greater belowground amino acid and flavonoid concentrations were observed to counteract anoxic stress in eutrophic sediments without mixed beach sand. This led to more positive belowground stable sulfur isotope ratios in eutrophic sediments with a lower Eh.

CONCLUSIONS

These results indicated that coarse beach sand indirectly enhanced photosynthesis in T. hemprichii by reducing sulfide intrusion with lower amino acid and flavonoid concentrations. This could explain why T. hemprichii often grows better on coarse sand substrates. Therefore, it is imperative to consider adding beach sand to sediments to improve the environmental conditions for seagrass and restore seagrass in eutrophic ecosystems.

Seagrass wasting disease: Nitrate enrichment and exposure to a herbicide (Diuron) increases susceptibility of Zostera marina to infection

Seagrass meadows suffered large-scale declines in the past century. The 'wasting disease', pathognomonically associated with Labyrinthula zosterae, reduced populations of Zostera marina on both sides of the North Atlantic in, and since, the 1930s, coinciding with intensive agricultural use of artificial fertilizers and herbicides. This study tests the long-standing hypothesis that nutrient enrichment and a herbicide increases vulnerability to pathogens. Z. marina shoots from the Thames Estuary grown in elevated nitrate concentrations had significantly higher rates of infection by L. zosterae than controls, but not by Aplanochytrium sp., another slime-mould like protist. Z. marina shoots grown in 2μg·l^-1 Diuron solutions and infected separately by L. zosterae and Aplanochytrium sp. had significantly higher wasting indices than controls. The results identified Aplanochytrium sp. as another opportunistic pathogen causing a seagrass wasting-type disease and support the hypothesis that pollution by herbicides and nitrate increases the susceptibility of Z. marina to infections.

Multiple Consequences Induced by Epidermally-Located Anthocyanins in Young, Mature and Senescent Leaves of Prunus

Anthocyanic morphs are generally less efficient in terms of carbon gain, but, in turn, are more photoprotected than anthocyanin-less ones. To date, mature leaves of different morphs or leaves at different developmental stages within the same species have generally been compared, whereas there is a lack of knowledge regarding different stages of development of red vs. green leaves. Leaves (1-, 7-, and 13-week-old) of red- (RLP) and green-leafed (GLP) Prunus in terms of photosynthetic rate, carbon metabolism and photoprotective mechanisms were compared to test whether anthocyanin-equipped leaves perform better than anthocyanin-less leaves and whether photoprotection is the primary role of epidermally-located anthocyanins, using for the first time a recently-developed parameter of chlorophyll fluorescence (qPd). GLP leaves had a higher photosynthetic rate in 1- and 7-week-old leaves, but RLP leaves performed better at an early stage of senescence and had a longer leaf lifespan. Anthocyanins contributed to leaf photoprotection throughout the leaf development, but were tightly coordinated with carotenoids. Besides photoprotecting, we propose that epidermal anthocyanins may be principally synthetized to maintain an efficient carbon-sink strength in young and senescent leaves, thus extending the RLP leaf lifespan.

Juvenile Coffee Leaves Acclimated to Low Light Are Unable to Cope with a Moderate Light Increase

The understorey origin of coffee trees and the strong plasticity of Coffea arabica leaves in relation to contrasting light environments have been largely shown. The adaptability of coffee leaves to changes in light was tested under controlled conditions by increasing the illumination rate on C. arabica var. Naryelis seedlings acclimated to low light conditions and observing leaf responses at three different developmental stages (juvenile, growing and mature). Only mature leaves proved capable of adapting to new light conditions. In these leaves, different major mechanisms were found to contribute to maintaining a good photosynthetic level. With increased illumination, a high photosynthetic response was conserved thanks to fast nitrogen remobilization, as indicated by SPAD values and the photorespiration rate. Efficient photoprotection was accompanied by a great ability to export sucrose, which prevented excessive inhibition of the Calvin cycle by hexose accumulation. In contrast, in younger leaves, increased illumination caused photodamage, observable even after 9 days of treatment. One major finding was that young coffee leaves rely on the accumulation of chlorogenic acids, powerful antioxidant phenolic compounds, to deal with the accumulation of reactive oxygen species rather than on antioxidant enzymes. Due to a lack of efficient photoprotection, a poor ability to export sucrose and inadequate antioxidant protection, younger leaves seemed to be unable to cope with increased illumination. In these leaves, an absence of induced antioxidant enzyme activity was accompanied, in growing leaves, by an absence of antioxidant synthesis or, in juvenile leaves, inefficient synthesis of flavonoids because located in some epidermis cells. These observations showed that coffee leaves, at the beginning of their development, are not equipped to withstand quick switches to higher light levels. Our results confirm that coffee trees, even selected for full sunlight conditions, remain shade plants possessing leaves able to adapt to higher light levels only when mature.

Current European Labyrinthula zosterae are not virulent and modulate seagrass (Zostera marina) defense gene expression

Pro- and eukaryotic microbes associated with multi-cellular organisms are receiving increasing attention as a driving factor in ecosystems. Endophytes in plants can change host performance by altering nutrient uptake, secondary metabolite production or defense mechanisms. Recent studies detected widespread prevalence of Labyrinthula zosterae in European Zostera marina meadows, a protist that allegedly caused a massive amphi-Atlantic seagrass die-off event in the 1930's, while showing only limited virulence today. As a limiting factor for pathogenicity, we investigated genotype × genotype interactions of host and pathogen from different regions (10-100 km-scale) through reciprocal infection. Although the endophyte rapidly infected Z. marina, we found little evidence that Z. marina was negatively impacted by L. zosterae. Instead Z. marina showed enhanced leaf growth and kept endophyte abundance low. Moreover, we found almost no interaction of protist × eelgrass-origin on different parameters of L. zosterae virulence/Z. marina performance, and also no increase in mortality after experimental infection. In a target gene approach, we identified a significant down-regulation in the expression of 6/11 genes from the defense cascade of Z. marina after real-time quantitative PCR, revealing strong immune modulation of the host's defense by a potential parasite for the first time in a marine plant. Nevertheless, one gene involved in phenol synthesis was strongly up-regulated, indicating that Z. marina plants were probably able to control the level of infection. There was no change in expression in a general stress indicator gene (HSP70). Mean L. zosterae abundances decreased below 10% after 16 days of experimental runtime. We conclude that under non-stress conditions L. zosterae infection in the study region is not associated with substantial virulence.

Light-induced variation in phenolic levels in foliage of rain-forest plants : I. Chemical changes

Levels of phenolic secondary metabolites in the leaves of four west African rain-forest plants,Acacia pennata, Cynometra leonensis, Diopyros thomasii, andTrema guineensis, were correlated with incident light intensity at both the inter- and intraindividual level. Enhanced phenolic levels under high light intensity appeared to be due to production of both polyphenolics (condensed and hydrolyzable tannins) and simple phenolics. InTrema guineensis, where it is possible to separate leaves in terms of both their age and the light incident upon them, condensed tannin production progressed differently during the development of "sun" and "shade" leaves, suggesting continuing production of new oligomers in the former but not in the latter. The results of this study suggest that the production of phenolics in relation to variation in incident light is a finely tuned process, which must be explained in terms of plant physiology and intermediate metabolism rather than in terms of resource allocation or a direct response to herbivory.

Extraction of tannin from fresh and preserved leaves

The extractability of tannin from fresh, lyophilized, and dried leaves collected at various times in the growing season was determined using the radial diffusion assay for protein-precipitating phenolics. The amount of tannin extracted depended on the method of leaf preservation and on the maturity of the leaf. Early in the season, more tannin was extracted from lyophilized leaves than from fresh leaves, but late in the season more tannin was extracted from fresh leaves. At all times, more tannin was extracted with aqueous acetone than with aqueous or acidic methanol.

Effects of latitude-related factors and geographical origin on anthocyanidin concentrations in fruits of Vaccinium myrtillus L. (bilberries)

Two data sets are presented to identify the effect of growth location and origin of parental plant on anthocyanidin concentrations in Vaccinium myrtillus fruits. Bilberries were collected from wild populations growing at different latitudes and from cultivated plants originating from different geographical locations but grown in the same location for over 10 years. High-performance liquid chromatography analysis showed that anthocyanidin concentrations varied significantly with latitude and with geographical origin, with higher values form northern latitudes or from a more northerly origin of parent plants. The results show that anthocyanidin concentrations in bilberries are under strong genetic control but are also influenced by climatic factors. Furthermore, the proportions of specific anthocyanidins differed between latitudes and between plants with different parental origins. The diversity in anthocyanidin concentration and composition has important implications for plant breeders and for future development of varieties with high antioxidant capacity.

Synthesis of phenolics and flavonoids in ginger (Zingiber officinale Roscoe) and their effects on photosynthesis rate

The relationship between phenolics and flavonoids synthesis/accumulation and photosynthesis rate was investigated for two Malaysian ginger (Zingiber officinale) varieties grown under four levels of glasshouse light intensity, namely 310, 460, 630 and 790 μmol m(-2)s(-1). High performance liquid chromatography (HPLC) was employed to identify and quantify the polyphenolic components. The results of HPLC analysis indicated that synthesis and partitioning of quercetin, rutin, catechin, epicatechin and naringenin were high in plants grown under 310 μmol m(-2)s(-1). The average value of flavonoids synthesis in leaves for both varieties increased (Halia Bentong 26.1%; Halia Bara 19.5%) when light intensity decreased. Photosynthetic rate and plant biomass increased in both varieties with increasing light intensity. More specifically, a high photosynthesis rate (12.25 μmol CO(2) m(-2)s(-1) in Halia Bara) and plant biomass (79.47 g in Halia Bentong) were observed at 790 μmol m(-2)s(-1). Furthermore, plants with the lowest rate of photosynthesis had highest flavonoids content. Previous studies have shown that quercetin inhibits and salicylic acid induces the electron transport rate in photosynthesis photosystems. In the current study, quercetin was an abundant flavonoid in both ginger varieties. Moreover, higher concentration of quercetin (1.12 mg/g dry weight) was found in Halia Bara leaves grown under 310 μmol m(-2)s(-1) with a low photosynthesis rate. Furthermore, a high content of salicylic acid (0.673 mg/g dry weight) was detected in Halia Bara leaves exposed under 790 μmol m(-2)s(-1) with a high photosynthesis rate. No salicylic acid was detected in gingers grown under 310 μmol m(-2)s(-1). Ginger is a semi-shade loving plant that does not require high light intensity for photosynthesis. Different photosynthesis rates at different light intensities may be related to the absence or presence of some flavonoid and phenolic compounds.

Effects of fish farming on flavonoids in Posidonia oceanica

This work is a first approach to flavonoid responses (total proanthocyanidins and total and simple flavonols) in Posidonia oceanica in function of nutrient enrichment (aquaculture activities - fish farming), in the western Mediterranean Sea (Calvi-Corsica-France). The first result is the presence of total and simple flavonoids in P. oceanica. The second result shows an increase in total proanthocyanidin and total flavonol concentrations near cages, which would be linked to the high grazing pressure induced by meadow enrichment. Concerning simple flavonols, only quercetin shows a response to fish farming, which could be due to its strong antioxidant capacity. The presence of fish farming, which causes variations in environmental parameters, could affect the functioning of P. oceanica meadows. Flavonoid concentrations in P. oceanica seem to be a possible bioindicator of nutrient enrichment for the management of the littoral environment.

Relationships between optically assessed polyphenols and chlorophyll contents, and leaf mass per area ratio in woody plants: a signature of the carbon-nitrogen balance within leaves?

Chlorophyll (Chl) and epidermal polyphenol (EPhen) contents were estimated in vivo using two optical leaf-clips, SPAD-502 and Dualex, respectively. The area-based measurements were transformed into mass-based data by taking into account the leaf dry mass per area (LMA). Measurements were performed on forest trees and on saplings grown under controlled conditions. While LMA increased with irradiance along a vertical transect in a beech canopy or in saplings grown under different and increasing irradiance levels, mass-based EPhen (EPhen(m)) increased, whereas mass-based Chl (Chl(m)) decreased. This was a signature of a gradual switch of investment from protein into polyphenol production. A similar signature was obtained in saplings grown on nitrogen-deficient soil with respect to fertilized controls. However, nitrogen effects remained moderate compared to irradiance-induced effects. EPhen(m) and Chl(m) both declined with plant ageing-induced increases in LMA, under all tested growth conditions. This was a signature of an accumulation of dry matter that diluted Chl and EPhen. The described competition between Chl and EPhen in leaves fits well with the predictions of the Protein Competition Model (PCM), that is, that the total leaf mass-based polyphenols content (Phen(t)) is controlled by the competition between protein and polyphenol biosynthetic pathways and its metabolic regulation.

Do carbon-based defences reduce foliar damage? Habitat-related effects on tree seedling performance in a temperate rainforest of Chiloé Island, Chile

Carbon-based secondary compounds (CBSCs), such as phenols or tannins, have been considered as one of the most important and general chemical barriers of woody plants against a diverse array of herbivores. Herbivory has been described as a critical factor affecting the growth and survival of newly established tree seedlings or juveniles then, the presence of secondary metabolites as defences against herbivores should be a primary strategy to reduce foliar damage. We examined whether light-induced changes in leaf phenolic chemistry affected insect herbivory on seedlings of two rainforest tree species, Drimys winteri (Winteraceae) and Gevuina avellana (Proteaceae). Seedlings of both species were planted under closed canopy and in a canopy gap within a large remnant forest patch. Half of the seedlings in each habitat were disinfected with a wide-spectrum systemic insecticide and the other half were used as controls. Seedling growth, survival, and foliar damage (estimated by an herbivory index) due to insect herbivores were monitored over a period of 16 months (December 2001-April 2003). The total leaf content of phenols and condensed tannins were assessed in seedlings from both habitats. As expected, access to light induced a greater production of CBSCs in seedlings of both tree species, but these compounds did not seem to play a significant defensive role, as seedlings grown in gaps suffered greater leaf damage than those planted in forest interior. In addition, in both habitats, seedlings without insecticide treatment suffered a greater foliar damage than those with insecticide, especially 16 months after the beginning of the experiment. Canopy openness and herbivory had positive and negative effects, respectively, on seedling growth and survival in both tree species. In conclusion, despite the higher levels of defence in tree-fall gap, the higher densities of herbivore override this and lead to higher damage levels.

Out of the quagmire of plant defense hypotheses

Several hypotheses, mainly Optimal Defense (OD), Carbon: Nutrient Balance (CNB), Growth Rate (GR), and Growth-Differentiation Balance (GDB), have individually served as frameworks for investigating the patterns of plant defense against herbivores, in particular the pattern of constitutive defense. The predictions and tests of these hypotheses have been problematic for a variety of reasons and have led to considerable confusion about the state of the "theory of plant defense." The primary contribution of the OD hypothesis is that it has served as the main framework for investigation of genotypic expression of plant defense, with the emphasis on allocation cost of defense. The primary contribution of the CNB hypothesis is that it has served as the main framework for investigation of how resources affect phenotypic expression of plant defense, often with studies concerned about allocation cost of defense. The primary contribution of the GR hypothesis is that it explains how intrinsic growth rate of plants shaped evolutionarily by resource availability affects defensive patterns. The primary contribution of the expanded GDB hypothesis is that it recognizes the constant physiological tradeoff between growth and differentiation at the cellular and tissue levels relative to the selective pressures of resource availability, including explicitly taking into account plant tolerance of damage by enemies. A clearer understanding of these hypotheses and what we have learned from investigations that use them can facilitate development of well-designed experiments that address the gaps in our knowledge of plant defense.

Growth and alkaloid contents in leaves of Tabernaemontana pachysiphon Stapf (Apocynaceae) as influenced by light intensity, water and nutrient supply

The growth of Tabernaemontana pachysiphon (Apocynaceae) plants and the alkaloid content of leaves were investigated in the greenhouse at three levels of nutrient supply under two contrasting water and light regimes. We determined height increment, above-ground biomass production, leaf size, specific leaf weight and the content of the alkaloids apparicine, A2, isovoacangine, tubotaiwine and tubotaiwine-N-oxide. The effects of major controlling factors such as light, water and nutrient supply could be directly correlated with growth and were largely independent of each other. In contrast, leaf-alkaloid contents were influenced by interdependencies among the main factors and individually affected in a synergistic or antagonistic manner which deviated from the effects on growth. The following general trends could be identified with respect to the quantitatively predominant alkaloids apparicine, tubotaiwine and isovoacangine. Increasing nutrient supply had a positive effect on both growth and alkaloid content. Drought increased alkaloid content, but retarded growth. High light intensity lowered alkaloid content but promoted growth. We investigated the relationship between primary production and the production of secondary metabolites with respect to relative and total alkaloid content as well as in relation to the leaves' nitrogen status. Our results showed that under conditions of low nutrient supply, higher proportions of leaf nitrogen were allocated to alkaloids than at moderate or high nutrient supply. Under conditions of drought and low light, all plants allocated almost equal proportions of leaf nitrogen to alkaloids, regardless of fertiliser. Total alkaloid content per plant, however, increased with fertilisation. With respect to the N-allocation strategy, we found no indication of a trade-off between primary production and the production of secondary metabolites in this species. Rather, our results are in accordance with the carbon nutrient balance hypothesis.

Resource availability and the trichome defenses of tomato plants

We conducted two experiments to determine how resource availability influenced allocation by tomato (Lycopersicon esculentum) to trichomes, and how different patterns of trichome allocation by plants grown in different resource environments might then influence the behavior of tobacco hornworm (Manduca sexta) caterpillars. In the first experiment we used high and low levels of light and water, and then, using scanning electron microscopy, determined trichome densities on the leaves and stems. We sampled leaves and stems at several places throughout the plant to determine whether there were within-plant differences in allocation to trichomes. The results of the first experiment showed that resource availability influenced allocation to trichome growth. Patterns in high and low-light supported both the growth-differentiation balance hypothesis (GDBH) and the carbon-nutrient balance hypothesis (CNBH). However, the GDBH was not supported by differences among water treatments. Contrary, to predictions of the GDBH, plants with intermediate growth did not have the highest trichome densities, and plants with similar growth differed in trichome density. Possible biological and artifactual explanations are discussed. The first experiment also showed that there was within-plant variation in allocation to trichomes, and that plant resource availability may influence within-plant variation in allocation to trichomes. In the second experiment, we grew plants in high and low-light, and then monitored the behavior of tobacco hornworms on the stems of these plants in the laboratory. This experiment demonstrated that the light environment that tomato plants were grown in influenced the resting behavior of caterpillars. Furthermore, it demonstrated that both glandular and non-glandular trichomes impeded caterpillars from searching for food. Overall, this study indicated that plant resource availability can influence allocation to trichome defenses, and that these differences may affect insect herbivores.

Carbon/nutrient balance as a predictor of plant defense in Alaskan balsam poplar: Potential importance of metabolite turnover

The carbon/nutrient balance hypothesis fails to correctly predict effects of fertilization and shading on concentrations of defensive metabolites in Alaskan balsam poplar (Populus balsamifera). Of six metabolites analyzed, only one responded in the predicted fashion to fertilization and one to shading. These results and those of other similar studies suggest that while the carbon/nutrient balance hypothesis may correctly predict the effects of fertilization and shading on the concentrations of metabolic "end products", it fails for many metabolites because of the dynamics associated with their production and turnover. In metabolites that turn over, static concentration is a poor predictor of defensive investment.

Response of winter chemical defense in Alaska paper birch and green alder to manipulation of plant carbon/nutrient balance

Plant carbon/nutrient balance has been implicated as an important factor in plant defensive chemistry and palatability to herbivores. We tested this hypothesis by fertilizing juvenile growth form Alaska paper birch and green alder with N, P and N-plus-P in a balanced 2x2 factorial experiment. Additionally, we shaded unfertilized plants of both species. Fertilization with N and N-plus-P increased growth of Alaska paper birch, reduced the concentration of papyriferic acid in internodes and increased the palatability of birch twigs to snowshoe hares. Shading decreased birch growth, decreased the concentration of papyriferic acid in internodes and increased twig palatability. These results indicate that the defensive chemistry and palatability of winter-dormant juvenile Alaska paper birch are sensitive to soil fertility and shade. Conversely the defensive chemistry and palatability of green alder twigs to snowshoe hares were not significantly affected by soil fertility or shade. The greater sensitivity of Alaska paper birch defensive chemistry and palatability to snowshoe hares in comparison to green alder is in agreement with the hypothesis that early successional woody plants that are adapted to high resource availability are more plastic in their chemical responses to the physical environment than are species from less favorable environments.