Water regime and growth of young oak stands subjected to air-warming and drought on two different forest soils in a model ecosystem experiment.

Global climate change is expected to increase annual temperatures and decrease summer precipitation in Central Europe. Little is known of how forests respond to the interaction of these climate factors and if their responses depend on soil conditions. In a 3-year lysimeter experiment, we investigated the growth response of young mixed oak stands, on either acidic or calcareous soil, to soil water regime, air-warming and drought treatments corresponding to an intermediate climate change scenario. The air-warming and drought treatments were applied separately as well as in combination. The air-warming treatment had no effect on soil water availability, evapotranspiration or stand biomass. Decreased evapotranspiration from the drought-exposed stands led to significantly higher air and soil temperatures, which were attributed to impaired transpirational cooling. Water limitation significantly reduced the stand foliage, shoot and root biomass as droughts were severe, as shown in low leaf water potentials. Additional air warming did not enhance the drought effects on evapotranspiration and biomass, although more negative leaf water potentials were observed. After re-watering, evapotranspiration increased within a few days to pre-drought levels. Stands not subjected to the drought treatment produced significantly less biomass on the calcareous soil than on the acidic soil, probably due to P or Mn limitation. There was no difference in biomass and water regime between the two soils under drought conditions, indicating that nutrient availability was governed by water availability under these conditions. The results demonstrate that young oak stands can cope with severe drought and therefore can be considered for future forestry.

Recent achievements and trends in experimental plant biology.

Between 21 and 25 September 2009, Krakow hosted the 4th Conference of the Polish Society of Experimental Plant Biology, co-organized with the Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, and supported by the Biochemical Society. The aim of the conference was to present and discuss the most important topics in different disciplines of plant experimental science as well as to facilitate the interaction and co-operation between scientists. To achieve this goal, about 30 top specialists in various areas of plant biology were invited to give plenary lectures in the following sessions: Plant structure and development; Plant-microbial interactions; Mitochondria and chloroplasts in cell metabolism; Stress tolerance in plants; Structural and functional organization of plant genomes; Mutants in developmental and metabolic studies; Secondary metabolites as pharmaceutics and nutraceutics; Plant membranes; and Integrating plant functions via signalling molecules: molecular mechanisms. Some of the main problems highlighted in the plenary lectures are briefly summarized in the present paper. Two poster sessions enabled a discussion of over 200 posters presented. The conference had an international character, its official language was English, and among the more than 350 participants, about 60 were from abroad. Several plenary lectures were prepared as short review papers and they are published in this issue of Biochemical Society Transactions.

Effects of floral thermogenesis on pollen function in Asian skunk cabbage Symplocarpus renifolius.

The effects of temperature on pollen germination and pollen tube growth rate were measured in vitro in thermogenic skunk cabbage, Symplocarpus renifolius Schott ex Tzvelev, and related to floral temperatures in the field. This species has physiologically thermoregulatory spadices that maintain temperatures near 23 degrees C, even in sub-freezing air. Tests at 8, 13, 18, 23, 28 and 33 degrees C showed sharp optima at 23 degrees C for both variables, and practically no development at 8 degrees C. Thermogenesis is therefore a requirement for fertilization in early spring. The narrow temperature tolerance is probably related to a long period of evolution in flowers that thermoregulate within a narrow range.

Marker-assisted genotype analysis of bulb colors in segregating populations of onions (Allium cepa).

Bulb color in onions (Allium cepa) is an important trait whose complex inheritance mechanism involves epistatic interactions among major color-related loci. Recent studies revealed that inactivation of dihydroflavonol 4-reductase (DFR) in the anthocyanin synthesis pathway was responsible for the color differences between yellow and red onions, and two recessive alleles of the anthocyanidin synthase (ANS) gene were responsible for a pink bulb color. Based on mutations in the recessive alleles of these two genes, PCR-based markers for allelic selection were developed. In this study, genotype analysis of onions from segregating populations was carried out using these PCR-based markers. Segregating populations were derived from the cross between yellow and red onions. Five yellow and thirteen pink bulbs from one segregating breeding line were genotyped for the two genes. Four pink bulbs were heterozygous for the DFR gene, which explains the continuous segregation of yellow and pink colors in this line. Most pink onions were homozygous recessive for the ANS gene, except for two heterozygotes. This finding indicated that the homozygous recessive ANS gene was primarily responsible for the pink color in this line. The two pink onions, heterozygous for the ANS gene, were also heterozygous for the DFR gene, which indicated that the pink color was produced by incomplete dominance of a red color gene over that of yellow. One pink line and six other segregating breeding lines were also analyzed. The genotyping results matched perfectly with phenotypic color segregation.

Characterization of the maize xylem sap proteome.

The xylem in plants has mainly been described as a conduit for water and minerals, but emerging evidence also indicates that the xylem contains protein. To study the proteins in xylem sap, we characterized the identity and composition of the maize xylem sap proteome. The composition of the xylem sap proteome in maize revealed proteins related to different phases of xylem differentiation including cell wall metabolism, secondary cell wall synthesis, and programmed cell death. Many proteins were found to be present as multiple isoforms and some of these isoforms are glycosylated. Proteins involved in defense mechanisms were also present in xylem sap and the sap proteins were shown to have antifungal activity in bioassays.

The regulation from guaiacyl to syringyl lignin in the differentiating xylem of Robinia pseudoacacia.

13C- and deuterium (D)-labeled ferulic acid and sinapic acid ([8-(13)C, 3-OCD3]-ferulic acid and [8-(13)C, 3,5-OCD3]-sinapic acid) were administered to robinia (Robinia pseudoacacia L.) shoots. To estimate the distribution of the label from administrated ferulic or sinapic acid, continuous 50-microm-thick tangential sections cut from the cambium of robinia were subjected to lignin chemical analysis by the DFRC method. Labeled ferulic acid was incorporated into guaiacyl and syringyl lignin. The incorporation of labeled ferulic acid into syringyl units was observed only in the later stage of lignification. Labeled sinapic acid was incorporated into syringyl lignin in the early stage and the later stage of lignification. In general, syringyl lignin was deposited in the later stage of cell wall lignification. Thus, the incorporation of sinapic acid to syringyl lignin in the early stage of lignification was abnormal. Taken together, the aromatic ring-modifying reactions (the conversion from guaiacyl to syringyl moiety, including the hydroxylation and methylation) were more important for the regulation of the sinapyl alcohol biosynthesis than the reducing reactions (the reduction of acids to alcohols) in the differentiating xylem.

Communication between animal cells and the plant foods they ingest: phyto-zooidal dependencies and signaling (Review).

The beneficial effect of plant foods on human health is unmistakable. Time and time again, studies have found foods of plant origin to reduce the risk of most major chronic illnesses suffered by the human population. Possible mechanisms for the preventative effects of these foods are discussed. Each of the plant groups reviewed was found to reduce the risk of one or more of the following: cardiovascular disease, cancer (lung, breast, colon, rectal, prostate, epithelial, stomach, esophageal, oral, pharynx, larynx, urinary tract, endometrium, pancreas, thyroid, liver, ovary, gallbladder, bladder, and kidney), diabetes, hypertension, bone degeneration, diverticulitis, constipation, gallstones, age-related blindness. Almost no evidence was found to suggest a negative effect on health due to consumption of these plant foods. Based on this material and a review of conserved animal signaling molecules we surmise that animals require these chemicals to enhance specific mammalian cellular processes, demonstrating phyto-zooidal signaling. Further, this diet dependency coupling between plants and animals probably evolved because of the abundance of a particular plant material in a local environment, which is now broken because of technological advances. In conclusion, the overwhelming majority of evidence shows that people may significantly decrease their risks of the aforementioned diseases by increasing their intake of these foods since they represent a natural method to enhance animal processes and signaling.

Structure and function of shisham forests in central Himalaya, India: nutrient dynamics.

The structure and function of Shisham (Dalbergia sissoo Roxb.) forests were investigated in relation to nutrient dynamics in 5- to 15-year-old stands growing in central Himalaya. Nutrient concentrations and storage in different layers of vegetation were in the order: tree > shrub > herb. Forest soil, litter and vegetation accounted for 80.1-91.9, 1.0-1.5 and 7.0-18.4%, respectively, of the total nutrients in the system. There were considerable reductions (trees 32.8-43.1; shrubs 26.2-32.4; and herbs 18-8-22-2%) in nutrient concentrations of leaves during senescence. Nutrient uptake by the vegetation as a whole and also by the different components, with and without adjustment for internal recycling, was investigated. Annual transfer of litter nutrients to the soil from vegetation was 74.8-108.4 kg ha(-1) year(-1) N, 56.8-4 kg ha(-1) year(-1) P and 38.7-46.9 kg ha(-1) year(-1) K. Turnover rate and time for different nutrients ranged between 56 and 66 % year(-1) and 1.5 and 1.8 years, respectively. The turnover rate of litter indicates that over 50% of nutrients in litter on the forest floor are released, which ultimately enhances the productivity of the forest stand. The nutrient use efficiency in Shisham forests ranged from 136 to 143 kg ha(-1) year(-1) for N, 1,441 to 1,570 kg ha(-1) year(-1) for P and 305 to 311 kg ha(-1) year(-1) for K. Compared with natural oak forest (265 kg ha(-1) year(-1) and an exotic eucalypt plantation (18 kg ha(-1) year(-1), a higher proportion of nutrients was retranslocated in Shisham forests, largely because of higher leaf tissue nutrient concentrations. This indicates a lower nutrient use efficiency of Shisham compared with eucalypt and oak. Compartment models for nutrient dynamics have been developed to represent the distribution of nutrients pools and net annual fluxes within the system.

Types of pollen dispersal units in orchids, and their consequences for germination and fertilization.

The various pollen dispersal units (PDU) found in orchids are discussed together with possible evolutionary trends and the consequences for germination and fertilization. Orchids with monad and tetrad pollen form more complex dispersal units by means of pollenkitt, elastoviscin, a callosic wall, common walls or a combination of these. Evolutionary trends include (1) from pollenkitt to elastoviscin; (2) from monad to tetrads and multiples of tetrads; (3) from partially dehydrated (<30 %) to partially hydrated (>30 %) pollen; and (4) from monad pollen to PDUs with many pollen grains. The biological consequences concern both male and female reproductive systems. Some features of the male side are present in all orchids irrespective of the pollen dispersal unit, whereas other characters are found only in orchids with pollinia; the same applies for the female counterpart. Pollen grains of orchids with pollinia germinate at least 24 h after pollination because the pollen grains/tetrads must swell and make space for the growth of pollen tubes.

Functional andromonoecy in Euphorbia (Euphorbiaceae).

The occurrence of cyathia containing staminate flowers but lacking a pistillate flower was studied in 17 species of Euphorbia. Male cyathia were found in the majority of species studied (88.2%) giving functional andromonoecy. In the male cyathia, the pistillate flower is generally totally absent, but sometimes a vestigial pistillate flower with a non-functional ovary is present. The proportion of male cyathia varied at both the population and species level. The position of male cyathia within the inflorescence showed a constant pattern among species: the proportion of male cyathia decreased from the first to the last levels of the pleiochasia. In general, perennial species had significantly higher proportions of male cyathia than annual species (mean 20 and 2.3%, respectively). In annual species there was a trend for production of male cyathia only in the first level of the inflorescence, whereas in perennials production up to the fourth level of the inflorescence was usual. Functional andromonoecy is common in Euphorbia and represents a new sex segregation in the genus. The selective forces causing this secondary sex segregation in Euphorbia, such as improved pollination or increased outcrossing, are discussed.

Pollen production, microsporangium dehiscence and pollen flow in Himalayan cedar (Cedrus deodara Roxb. ex d. Don).

Microsporangium dehiscence, pollen production and dispersal were studied in Himalayan cedar (Cedrus deodara) during 1998 and 1999. Microsporangium dehiscence showed diurnal periodicity and was found to be related to air temperature and relative air humidity, with a strobilus taking 2 d to dehisce completely in warmer conditions and 3 d in cooler ones. The frequency of flowering in C. deodara was highly variable during the two successive years; however, cyclical production of pollen grains was observed in 50% of the trees. The maximum concentration of pollen grains in the air was found between 1200 and 1600 h, and this period was also noted to be the best time for pollination. Studying migration of pollen grains from isolated single trees in three directions showed that migration was not uniform in all directions. Long-distance transport of pollen grains was observed in the downhill direction. However, in the uphill and horizontal directions grains could travel only up to 97.5 and l95.1 m, respectively, and the frequency of pollen grains to the source frequency at these distances was only 1.9 and 2-5%, respectively. The results suggest that an isolation barrier of 190 m may be considered as a minimum for the management of deodar seed orchards.

Solving the puzzle of mirror-image flowers.

Enantiostyly is a plant sexual polymorphism in which female sex organs are deflected to the left or right -- resulting in 'mirror-image' flowers -- but, although it occurs in at least a dozen unrelated families of flowering plants, its adaptive significance has been unclear. Here we show that a mendelian locus governs the inheritance of style orientation and that this curious form of sexual asymmetry functions to promote cross-pollination in bee-pollinated plants.

The value of bees to the coffee harvest.

The self-pollinating African shrub Coffea arabica, a pillar of tropical agriculture, was considered to gain nothing from insect pollinators. But I show here that naturalized, non-native honeybees can augment pollination and boost crop yields by over 50%. These findings, together with world coffee-harvest statistics and results from field studies of organically shade-grown coffee, indicate that coffee plants would benefit from being grown in habitats that are suitable for sustaining valuable pollinators.

Geographic structure and dynamics of coevolutionary selection.

Coevolution of species is one of the major processes organizing the Earth's biodiversity. Recent coevolutionary theory has indicated that the geographic structure of species has the potential to impose powerful and continuing effects on coevolutionary dynamics, if that structure creates selection mosaics and coevolutionary hotspots across landscapes. Here we confirm that current coevolutionary selection in interspecific interactions can be highly divergent across both narrow and broad geographic scales, thereby fueling continuing coevolution of taxa. Study of a widespread plant insect interaction across a broad range of habitats for several years showed that an insect functioning both as a pollinator and a floral parasite can be strongly mutualistic in some habitats but commensal or antagonistic in neighbouring habitats. The results for one of the habitats span seven years, demonstrating that the local structure of coevolutionary selection can remain stable across multiple generations. Conservation of the evolutionary processes maintaining long-term biological diversity may require preservation of the conditions that allow a long-term shifting geographic mosaic of coevolutionary hotspots and coldspots.

Rapid changes in flowering time in British plants.

The average first flowering date of 385 British plant species has advanced by 4.5 days during the past decade compared with the previous four decades: 16% of species flowered significantly earlier in the 1990s than previously, with an average advancement of 15 days in a decade. Ten species (3%) flowered significantly later in the 1990s than previously. These data reveal the strongest biological signal yet of climatic change. Flowering is especially sensitive to the temperature in the previous month, and spring-flowering species are most responsive. However, large interspecific differences in this response will affect both the structure of plant communities and gene flow between species as climate warms. Annuals are more likely to flower early than congeneric perennials, and insect-pollinated species more than wind-pollinated ones.

Identification and characterization of the Arabidopsis PHO1 gene involved in phosphate loading to the xylem.

The Arabidopsis mutant pho1 is deficient in the transfer of Pi from root epidermal and cortical cells to the xylem. The PHO1 gene was identified by a map-based cloning strategy. The N-terminal half of PHO1 is mainly hydrophilic, whereas the C-terminal half has six potential membrane-spanning domains. PHO1 shows no homology with any characterized solute transporter, including the family of H(+)-Pi cotransporters identified in plants and fungi. PHO1 shows highest homology with the Rcm1 mammalian receptor for xenotropic murine leukemia retroviruses and with the Saccharomyces cerevisiae Syg1 protein involved in the mating pheromone signal transduction pathway. PHO1 is expressed predominantly in the roots and is upregulated weakly under Pi stress. Studies with PHO1 promoter-beta-glucuronidase constructs reveal predominant expression of the PHO1 promoter in the stelar cells of the root and the lower part of the hypocotyl. There also is beta-glucuronidase staining of endodermal cells that are adjacent to the protoxylem vessels. The Arabidopsis genome contains 10 additional genes showing homology with PHO1. Thus, PHO1 defines a novel class of proteins involved in ion transport in plants.

Recognition and rejection of self in plant reproduction.

Plant self-incompatibility (SI) systems are unique among self/nonself recognition systems in being based on the recognition of self rather than nonself. SI in crucifer species is controlled by highly polymorphic and co-evolving genes linked in a complex. Self recognition is based on allele-specific interactions between stigma receptors and pollen ligands that result in the arrest of pollen tube development. Commonalities and differences between SI and other self/nonself discrimination systems are discussed.

Pollinator-mediated selection on flower-tube length in a hawkmoth-pollinated Gladiolus (Iridaceae).

Darwin's mechanistic model whereby selection favours plants with flower tubes that exceed the tongue length of the primary pollinator, was tested using unmanipulated plants of the hawkmoth-pollinated South African iris, Gladiolus longicollis. The study population was characterized by exceptionally large phenotypic variation in flower-tube length (range 56-129 mm). Directional selection on tube length was revealed by a significant positive relationship between this trait and both fruit and seed set. Selection was attributed to the effect of tube length on pollen receipt, as supplemental hand pollinations showed fruit and seed set in the population to be pollen limited. Indirect selection on tube length may also occur through the correlation of this trait with inflorescence height, although direct selection on the latter trait was significant only for seed set. The main pollinators at the study site were individuals of the large hawkmoth Agrius convolvuli that had tongue lengths of 85-135 mm. Other hawkmoths had tongues that were much too short to reach the nectar in G. longicollis flowers and seldom carried pollen of G. longicollis. Flowers with tubes shorter than the tongues of A. convolvuli are apparently not effectively pollinated because stigmas do not contact the moth's head effectively. This study demonstrates that selection may occur among plants with natural phenotypic variation in flower-tube length, and supports Darwin's model of pollinator-mediated selection.