Erwin Beck

Specific and unspecific responses of plants to cold and drought stress

Different environmental stresses to a plant may result in similar responses at the cellular and molecular level. This is due to the fact that the impacts of the stressors trigger similar strains and downstream signal transduction chains. A good example for an unspecific response is the reaction to stressors which induce water deficiency e.g. drought, salinity and cold, especially frost. The stabilizing effect of liquid water on the membrane bilayer can be supported by compatible solutes and special proteins. At the metabolic level, osmotic adjustment by synthesis of low-molecular osmolytes (carbohydrates, betains, proline) can counteract cellular dehydration and turgor loss. Taking the example of Pinus sylvestris, changes at the level of membrane composition, and concomitantly of photosynthetic capacity during frost hardening is shown. Additionally the effect of photoperiod as measured via the phytochrome system and the effect of subfreezing temperatures on the incidence of frost hardening is discussed. Extremely hydrophilic proteins such as dehydrins are common products protecting not only the biomembranes in ripening seeds (late embryogenesis abundant proteins) but accumulate also in the shoots and roots during cold adaptation, especially in drought tolerant plants. Dehydrins are characterized by conserved amino acid motifs, called the K-, Y-or S-segments. Accumulation of dehydrins can be induced not only by drought, but also by cold, salinity, treatment with abscisic acid and methyl jasmonate. Positive effects of the overexpression of a wild chickpea (Cicer pinnatifidum) dehydrin in tobacco plants on the dehydration tolerance is shown. The presentation discusses the perception of cold and drought, the subsequent signal transduction and expression of genes and their products. Differences and similarities between the plant responses to both stressors are also discussed.

Gradients in a Tropical Mountain Ecosystem of Ecuador

Part I Introduction 1 The Ecosystem (Reserva Biologica San Francisco) E. Beck, F. Makeschin, F. Haubrich, M. Richter, J. Bendix, C. Valerezo 2 Mountain rain forests in southern Ecuador as a hotspot of biodiversity - Limited knowledge and diverging patterns G. Brehm, J. Homeier, K. Fiedler, I. Kottke, J. Illig, N.M. Noske, F. Werner, S-W. Breckle 3 The people settled around Podocarpus National Park P. Pohle 4 Ecuador suffers the highest deforestation rate in South America R. Mosandl, S. Gunter, B. Stimm, M. Weber 5 Methodological challenges of a megadiverse ecosystem G. Brehm, K. Fiedler, Ch. Hauser, H. Dalitz Part II Gradients in ecosystem analysis 6 Why investigating gradients in ecosystem analysis K. Fiedler, E. Beck 7 The investigated gradients E. Beck, R. Mosandl, M. Richter, I. Kottke Part III The altitudinal gradient Part III.1 Gradual changes along the altitudinal gradient 8 Climate J. Bendix, R. Rollenbeck, M. Richter, P. Fabian, P. Emck 9 Soils along the altitudinal transect and in catchments W. Wilcke, S. Yasin, A Schmitt, C. Valarezo, W. Zech 10 Flora: Composition and function 10.1 Potential vegetation and floristic composition of Andean forests in South Ecuador, with a focus on the RBSF J. Homeier, F. A. Werner, S. R. Gradstein, S -W. Breckle, M. Richter 10.2 Past vegetation and fire dynamics H. Niemann & H. Behling 10.3 Forest structure along an altitudinal gradient in southern Ecuador A. Paulsch, D. Piechowski, K. Muller-Hohenstein 10.4 Vegetation structures and ecological features of the upper timberline ecotone M. Richter, K.-H. Diertl, Th. Peters, R. W. Bussman 10.5 Mycorrhizal state and new and special features of mycorrhizae of trees, ericads, orchids, ferns andliverworts I. Kottke, A. Beck, I. Haug, S. Setaro, V. Jeske, J.P. Suarez, L. Paxmino, M. Preussing, M, Nebel, F. Oberwinkler 11 Fauna: Composition and function 11.1 Bird species distribution along an altitudinal gradient in southern Ecuador and its functional relationships with vegetation structure D. Paulsch and K. Muller-Hohenstein 11.2 Seed dispersal by birds, bats and wind F. Matt, K. Almeida, A. Arguero, C. Reudenbach 11.3 Variation of diversity patterns across moth families along a tropical elevational gradient K. Fiedler, G. Brehm, N. Hilt, D. Sussenbach, and C.L. Hauser 11.4 Soil fauna M. Maraun, J. Illig , D. Sandman,V. Krashevskaya, R.A. Norton, S. Scheu Part III.2 Processes along and within the gradient 12 Water relations W. Wilcke, S. Yasin, K. Fleischbein, R. Goller, J. Boy, J. Knuth, C. Valarezo, W. Zech 13 Nutrient status and fluxes at the field and catchment scale W. Wilcke, S.Yasin, K. Fleischbein, R. Goller, J. Boy, J. Knuth, C. Valarezo, W. Zech 14 Biotic soil activities S. Iost, F. Makeschin, M. Abiy, F. Haubrich 15 Elevational changes in stand structure and biomass allocation of tropical mountain forests in relation to microclimate and soil chemistry G. Moser, M. Roderstein, N. Soethe, D. Hertel, C. Leuschner 16 Stand structure, transpiration responses in trees and vines and stand transpiration of different forest types within the mountain rainforest M. Kuppers, T. Motzer,D. Schmitt., C. Ohlemacher, R. Zimmermann, V. Horna, B.I.L. Kuppers, T. Mette 17 Plant growth along the altitudinal gradient-role of plant nutritional status, fine root activity, and soil properties N. Soethe, W. Wilcke, J. Homeier, J. Lehmann, C. Engels Part III.3 Gradient heterogeneities Part III.3.A Spatial heterogeneities 18 Spatial

Plant resistance to cold stress: Mechanisms and environmental signals triggering frost hardening and dehardening

This introductory overview shows that cold, in particular frost, stresses a plant in manifold ways and that the plant’s response, being injurious or adaptive, must be considered a syndrome rather than a single reaction. In the course of the year perennial plants of the temperate climate zones undergo frost hardening in autumn and dehardening in spring. Using Scots pine (Pinus sylvestris L.) as a model plant the environmental signals inducing frost hardening and dehardening, respectively, were investigated. Over 2 years the changes in frost resistance of Scots pine needles were recorded together with the annual courses of day-length and ambient temperature. Both act as environmental signals for frost hardening and dehardening. Climate chamber experiments showed that short day-length as a signal triggering frost hardening could be replaced by irradiation with far red light, while red light inhibited hardening. The involvement of phytochrome as a signal receptor could be corroborated by respective night-break experiments. More rapid frost hardening than by short day or far red treatment was achieved by applying a short period (6 h) of mild frost which did not exceed the plant’s cold resistance. Both types of signals were independently effective but the rates of frost hardening were not additive. The maximal rate of hardening was − 0.93°C per day and frost tolerance of < − 72°C was achieved. For dehardening, temperature was an even more effective signal than day-length.

Seasonal changes in structure and function of spruce chloroplasts.

SummarySeasonal changes of ultrastructure were studied by electron microscopy and by determining the chlorophyll and starch content of the plastids. Young plastids of spruce (Picea abies (L.) Karst.) first function as amyloplasts which store reserve material for the growth of the young needles. Then they develop a normal thylakoid system and produce assimilation starch during the day. In autumn, starch synthesis ceases and the plastids group together. In winter they swell and their membrane system becomes disorganized and reduced. With increasing temperatures in spring the chloroplasts recover, but then they accumulate large amounts of starch, which is not broken down during the night or even during a dark period of several days. As in the previous year they now function as amyloplasts providing reserve material for the new shoot. In summer these plastids are again converted into typical chloroplasts. The same seasonal changes of structure and function could be observed in chloroplasts from 2- or 3-year old needles. Thus these changes represent cyclic processes, which repeat each year. Features of slow aging are superimposed on to these cycles.

Seasonal changes in the utilization and turnover of assimilation products in 8-year-old Scots pine (Pinus sylvestris L.) trees

SummaryThe present study aimed at a physiological understanding of the seasonal changes of the carbohydrate patterns and levels in the various tissues of 8-year-old Scots pine (Pinus sylvestris L.) trees growing under ambient climatic conditions in the botanical garden at Bayreuth. The photosynthates of selected twig sections were labelled by 14CO2 fixation and after chase periods of 1 h up to 8 months, the distribution of radiocarbon in the whole trees was determined and the labelling of identified carbohydrates was compared with the levels of these compounds in the individual tissues. Bud break and sprouting in spring is exclusively supplied by the recent photosynthates of the previous years needles. During summer assimilates of the old needles were utilized for secondary growth of the axial system while growth of the recent-years shoots was supported by their own photosynthesis. In autumn, soluble carbohydrates were produced instead of starch, a major part of which in addition to recent photosynthates was utilized for root growth during the cold season. Another part of the autumnal storage material was incorporated into the cell walls of the latest xylem and phloem elements still in winter. A pronounced starch-oligosaccharide interconversion upon frost hardening, and its reversal in spring as has been described for deciduous trees, could not be observed. This was due to maintenance of photosynthetic capability even in the cold season and the replacement of consumed storage material especially in late winter and early spring by new photosynthates.

Cytokinins in the perennial herb Urtica dioica L. as influenced by its nitrogen status

The effect of nitrogen on the cytokinin relations of Urtica dioica, the stinging nettle, has been investigated. The plants were grown in quartz sand and nutrient solutions providing levels of nitrate ranging from 1 to 22 mM. Nitrogen supply did not affect biomass production within the range of 3–15 mM NO3-. However, the shoot: root ratio of biomass was significantly higher at 15 mM (standard plants) than at 3 mM (low-nitrogen plants) nitrate supply. The cytokinin patterns of the roots, stems and adult, as well as meristematic leaves of plants grown at these two levels of nitrate supply, were determined by means of high-performance liquid chromatography (HPLC) and immunoassays. Enzyme-linked immunosorbent assays (ELISAs) for zeatin riboside, dihydrozeatin riboside, isopentenyladenosine, benzyladenosine and o-hydroxybenzyladenosine enabled the quantification of 17 cytokinins, 13 of which were found in the various tissues of Urtica. trans-Zeatin and its conjugates were the predominant cytokinins in all examined samples. While the free base trans-zeatin and its O-glucoside were the major cytokinins in adult leaves, trans-zeatin riboside was prominent in the other tissues of at least the standard plants. Glucosides of the trans-zeatin type cytokinins were present only in lower amounts. However, considerable amounts of a compound, tentatively identified as cis-zeatin riboside-O-glucoside, were found, particularly in roots and meristematic leaves. Comparatively high amounts of trans-zeatin nucleotide as well as isopentenyladenosine phosphate were also demonstrated in these tissues. Analysis of the root-pressure exudates similarly showed trans-zeatin riboside and, at a lower concentration, trans-zeatin to be the only substantial components. In the low-nitrogen plants, shortage of nitrogen was manifest only in the roots; the nitrogen contents of the shoots did not respond to the nitrogen supply. Likewise, the total content of cytokinins in the shoots of the low-nitrogen plants equaled that of the standard-plant shoots, while it was lower by about 25% in the roots of the low-nitrogen plants. In the latter, the amounts of cytokinins exuded via the root-pressure fluid were also approximately 25% lower. Since the levels of only the trans-zeatin cytokinins in the roots showed a linear correlation with the shoot-to-root ratios, these cytokinins may play an important role in biomass partitioning in Urtica dioica.

Maize Root Phytase (Purification, Characterization, and Localization of Enzyme Activity and Its Putative Substrate)

Three phytase (EC 3.1.3.26) isoforms from the roots of 8-d-old maize (Zea mays L. var Consul) seedlings were separated from phosphatases and purified to near homogeneity. The molecular mass of the native protein was 71 kD, and the isoelectric points of the three isoforms were pH 5.0, 4.9, and 4.8. Each of the three isoforms consisted of two subunits with a molecular mass of 38 kD. The temperature and pH optima (40[deg]C, pH 5.0) of these three isoforms, as well as the apparent Michaelis constants for sodium inositol hexakisphosphate (phytate) (43, 25, and 24 [mu]M) as determined by the release of inorganic phosphate, were only slightly different. Phytate concentrations higher than 300 [mu]M were inhibitory to all three isoforms. In contrast, the dephosphorylation of 4-nitrophenyl phosphate was not inhibited by any substrate concentration, but the Michaelis constants for this substrate were considerably higher (137–157 [mu]M). Hydrolysis of phytate by the phytase isoforms is a nonrandom reaction. D/L-Inositol-1,2,3,4,5- pentakisphosphate was identified as the first and D/L-inositol-1,2,5,6-tetrakisphosphate as the second intermediate in phytate hydrolysis. Phytase activity was localized in root slices. Although phosphatase activity was present in the stele and the cortex of the primary root, phytase activity was confined to the endodermis. Phytate was identified as the putative native substrate in maize roots (45 [mu]g P g-1 dry matter). It was readily labeled upon supplying [32P]phosphate to the roots.

Frost hardening and photosynthetic performance of Scots pine (Pinus sylvestris L.) needles: I. Seasonal changes in the photosynthetic apparatus and its function

Abstract.Photosynthetic CO2 uptake, the photochemical efficiency of photosystem II, the contents of chlorophyll and chlorophyll-binding proteins, and the degree of frost hardiness were determined in three-year-old Scots pine (Pinus sylvestris L.) trees growing in the open air but under controlled daylength. The following conditions were compared: 9-h light period (short day), 16-h light period (long day), and natural daylength. Irrespective of induction by short-day photoperiods or by subfreezing temperatures, frost hardening of the trees was accompanied by a long-lasting pronounced decrease in the photosynthetic rates of one-year-old needles. Under moderate winter conditions, trees adapted to a long-day photoperiod, assimilated CO2 with higher rates than the short-day-treated trees. In the absence of strong frost, photochemical efficiency was lower under short-day conditions than under a long-day photoperiod. Under the impact of strong frost, photochemical efficiency was strongly inhibited in both sets of plants. The reduction in photosynthetic performance during winter was accompanied by a pronounced decrease in the content of chlorophyll and of several chlorophyll-binding proteins [light-harvesting complex (LHC)IIb, LHC Ib, and a chlorophyll-binding protein with MW 43 kDa (CP 43)]. This observed seasonal decrease in photosynthetic pigments and in pigment-binding proteins was irrespective of the degree of frost hardiness and was apparantly under the control of the length of the daily photoperiod. Under a constant 9-h daily photoperiod the chlorophyll content of the needles was considerably lower than under long-day conditions. Transfer of the trees from short-day to long-day conditions resulted in a significantly increased chlorophyll content, whereas the chlorophyll content decreased when trees were transferred from a long-day to a short-day photoperiod. The observed changes in photosynthetic pigments and pigment-binding proteins in Scots pine needles are interpreted as a reduction in the number of photosynthetic units induced by shortening of the daily light period during autumn. This results in a reduction in the absorbing capacity during the frost-hardened state.

Plant Desiccation Tolerance

Part I Introduction Chapter 1 Introduction D. Bartels, E. Beck and U. Luttge Part II The Organismic Level Chapter 2 Cyanobacteria : Habitats and Species B. Budel Chapter 3 Cyanobacteria: Multiple Stresses, Desiccation Tolerant Photosynthesis and Di-nitrogen Fixation U. Luttge Chapter 4 Eucaryotic Algae B. Budel Chapter 5 Lichens and Bryophytes - Habitats and Species M. Lakatos Chapter 6 Ecophysiology of Desiccation/Rehydration Cycles in Mosses and Lichens T. G. Green, L. G. Sancho and A. Pintado Chapter 7 Lichens and Bryophytes - Light Stress and Photoinhibition in Desiccation/ Rehydration Cycles: Mechanisms of Photoprotection U. Heber and U. Luttge Chapter 8 Evolution, Diversity and Habitats of Poikilohydrous Vascular Plants St. Porembski Chapter 9 Ecophysiology of Homoiochlorophyllous and Poikilochlorophyllous Desiccation-Tolerant Plants Z. Tuba and H. K. Lichtenthaler Chapter 10 Hydraulic Architecture of Vascular Plants E. Steudle Chapter 11 Drought, Desiccation and Oxidative Stress R. Scheibe and E. Beck Chapter 12 Chamaegigas intrepidus DINTER - an Aquatic Poikilohydric Angiosperm that is Perfectly Adapted to its Complex and Extreme Environmental Conditions W. Hartung and H. Heilmeier Part III The Cell Biological Level Chapter 13 Molecular Biology and Physiological Genomics of Dehydration Stress Ruth Grene, C. Vasquez-Robinet and H. J. Bohnert Chapter 14 Dehydrins: Molecular Biology, Structure and Function S. K. Eriksson and Pia Harryson Chapter 15 Understanding Vegetative Desiccation Tolerance Using Integrated Functional Genomics Approaches Within a Comparative Evolutionary Framework J. C. Cushman and M. J. Oliver Chapter 16 Resurrection Plants: Physiology and Molecular Biology D. Bartels and S. S. Hussain Part IV Synopsis Chapter 17 Synopsis D. Bartels, E. Beck and U. Luttge Subject Index

Exotic trees as nurse-trees for the regeneration of natural tropical forests

Abstract. It is a widely held view that plantations of exotic tree species in the tropics are harmful to the environment. Arguments are collected here from experience in tropical countries, showing that the canopies of exotic trees can exert protective functions and have a nurse effect for the regeneration of natural forest. This counterbalances the opinion that exotic tree plantations generally are detrimental.