CO2, light and temperature influence senescence and protein degradation in wheat leaf segments

Effects of environmental conditions influencing photosynthesis and photorespiration on senescence and net protein degradation were investigated in segments from the first leaf of young wheat (Triticum aestivum L. cv. Arina) plants. The segments were floated on H2O at 25, 30 or 35°C in continuous light (PAR: 50 or 150 µmol m−2 s−1) in ambient air and in CO2-depleted air. Stromal enzymes, including phosphoglycolate phosphatase, glutamine synthetase, ferredoxin-dependent glutamate synthase, phosphoribulokinase, and the peroxisomal enzyme, glycolate oxidase, were detected by SDS-PAGE followed by immunoblotting with specific antibodies. In general, the net degradation of proteins and chlorophylls was delayed in CO2-depleted air. However, little effect of CO2 on protein degradation was observed at 25°C under the lower level of irradiance. The senescence retardation by the removal of CO2 was most pronounced at 30°C and at the higher irradiance. The stromal enzymes declined in a coordinated manner. Immunoreactive fragments from the degraded polypeptides were in most cases not detectable. However, an insolubilized fragment of glycolate oxidase accumulated in vivo, especially at 25°C in the presence of CO2. Detection of this fragment was minimal after incubation at 30°C and completely absent on blots from segments kept at 35°C. In CO2-depleted air, the fragment was only weakly detectable after incubation at 25°C. The results from these investigations indicate that environmental conditions that influence photosynthesis may interfere with senescence and protein catabolism in wheat leaves.

Long-distance transport of cobalt and nickel in maturing wheat

Cobalt, nickel and strontium were introduced via flaps into leaf laminas or into the stem of maturing, intact winter wheat (Triticum aestivum L., cv. `Arina') grown under natural conditions in a field. Long-distance transport of these elements and the influence of the application date and of different application positions were investigated. The dry-matter accumulation in the grains was not markedly affected by the treatments as compared to untreated control plants. The phloem-immobile strontium served as a marker for the distribution of the xylem sap in the plants. After foliar application, nickel accumulated more rapidly and in higher quantities in the grains than cobalt. Therefore, nickel has a slightly better phloem mobility than cobalt. Regardless of the application date, a higher percentage of the two elements was transported from the flag leaf lamina than from the second or third lamina from the top to the grains. These results indicate that the leaf position is highly relevant for the transfer of the heavy metals investigated to the ear. Introduction into the stem led to a higher accumulation of nickel and cobalt in the grains than introduction into one of the leaves. An earlier feeding date caused a higher accumulation of nickel and cobalt in the grains when introduced into the stem. In contrast, no major differences between earlier and later feeding dates were detected when the elements were introduced into the leaves. Losses of the applied elements were detected during maturation and can be explained by leakage in the rain.

Influence of nitrogen deficiency on senescence and the amounts of RNA and proteins in wheat leaves

Senescence-associated coordination in amounts of enzymes localized in different cellular compartments were determined in attached leaves of young wheat (Triticum aestivum L. cv. Arina) plants. Senescence was initiated at the time of full leaf elongation based on declines in total RNA and soluble protein. Removal of N from the growth medium just at the time of full leaf elongation enhanced the rate of senescence. Sustained declines in the amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39), and a marked decrease in the rbcS transcripts, just after full leaf elongation indicated that Rubisco synthesis/degradation was very sensitive to the onset of senescence. Rubisco activase amount also declined during senescence but the proportion of rca transcript relative to the total poly A RNA pool increased 3-fold during senescence. Thus, continued synthesis of activase may be required to maintain functional Rubisco throughout senescence. N stress led to declines in the amount of proteins located in the chloroplast, the peroxisome and the cytosol. Transcripts of the Clp protease subunits also declined in response to N stress, indicating that Clp is not a senescence-specific protease. In contrast to the other proteins, mitochondrial NADH-glutamate dehydrogenase (EC 1.4.1.2) was relatively stable during senescence and was not affected by N stress. During natural senescence with adequate plant nitrate supply the amount of nitrite reductase (EC 1.7.7.1) increased, and those of glutamine synthetase (EC 1.4.7.1) and glutamate synthase (EC 6.3.1.2) were stable. These results indicated that N assimilatory capacity can continue or even increase during senescence if the substrate supply is maintained. Differential stabilities of proteins, even within the same cellular compartment, indicate that proteolytic activity during senescence must be highly regulated.

Moderately High Temperatures Inhibit Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase (Rubisco) Activase-Mediated Activation of Rubisco

We tested the hypothesis that light activation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is inhibited by moderately elevated temperature through an effect on Rubisco activase. When cotton (Gossypium hirsutum L.) or wheat (Triticum aestivum L.) leaf tissue was exposed to increasing temperatures in the light, activation of Rubisco was inhibited above 35 and 30°C, respectively, and the relative inhibition was greater for wheat than for cotton. The temperature-induced inhibition of Rubisco activation was fully reversible at temperatures below 40°C. In contrast to activation state, total Rubisco activity was not affected by temperatures as high as 45°C. Nonphotochemical fluorescence quenching increased at temperatures that inhibited Rubisco activation, consistent with inhibition of Calvin cycle activity. Initial and maximal chlorophyll fluorescence were not significantly altered until temperatures exceeded 40°C. Thus, electron transport, as measured by Chl fluorescence, appeared to be more stable to moderately elevated temperatures than Rubisco activation. Western-blot analysis revealed the formation of high-molecular-weight aggregates of activase at temperatures above 40°C for both wheat and cotton when inhibition of Rubisco activation was irreversible. Physical perturbation of other soluble stromal enzymes, including Rubisco, phosphoribulokinase, and glutamine synthetase, was not detected at the elevated temperatures. Our evidence indicates that moderately elevated temperatures inhibit light activation of Rubisco via a direct effect on Rubisco activase.

New evidence for the symbiosis between Tuber aestivum and Picea abies

The Burgundy truffle (Tuber aestivum Vittad.), an ectomycorrhizal fungus living in association with host plants, is one of the most exclusive delicacies. The symbiosis with deciduous oak, beech, and hazel dominates our concept of truffle ecophysiology, whereas potential conifer hosts have rarely been reported. Here, we present morphological and molecular evidence of a wildlife T. aestivum symbiosis with Norway spruce (Picea abies Karst.) and an independent greenhouse inoculation experiment, to confirm our field observation in southwest Germany. A total of 27 out of 50 P. abies seedlings developed T. aestivum ectomycorrhizae with a mean mycorrhization rate of 19.6 %. These findings not only suggest P. abies to be a productive host species under suitable biogeographic conditions but also emphasize the broad ecological amplitude and great symbiotic range of T. aestivum. While challenging common knowledge, this study demonstrates a significant expansion of the species' cultivation potential to the central European regions, where P. abies forests occur on calcareous soils.

Potential and limitations of Burgundy truffle cultivation

Burgundy truffles (Tuber aestivum syn. Tuber uncinatum) are the highly prized fruit bodies of subterranean fungi always occurring in ectomycorrhizal symbiosis with host plants. Successful cultivation can be achieved through artificial mycorrhization and outplanting of mostly oaks and hazel on suitable terrain. Here, we review ecological requirements, the influence of environmental factors, and the importance of molecular techniques for a successful cultivation of T. aestivum across Europe. The historical background and current knowledge of T. aestivum cultivation are discussed in light of its socioeconomic relevance.

Palaeoenvironmental changes in Central Europe (NE Poland) during the last 6200 years reconstructed from a high-resolution multi-proxy peat archive

Peat deposits from an ombrotrophic bog (north-eastern Poland) were analysed to reconstruct peatland development and environmental changes. This paper presents reconstructions of hydrological changes and plant succession over the last 6000 years. The methods included the high-resolution analysis of plant macrofossils, pollen and testate amoebae, supported by radiocarbon dating. Three main phases were identified in the history of the bog and surrounding woodland vegetation: 4000–400 BC, 400 BC–AD 1700 and AD 1700–2011. Except for terrestrialisation and the fen-to-bog transition phase, the development of bog vegetation was mainly dependent on the climate until approximately AD 1700. The dominant taxon in Gązwa bog was Sphagnum fuscum/rubellum. Woodland development was significantly affected by human activity at several time periods. The most visible human activity, manifested by the decline of deciduous species, occurred ca. 350 BC, ca. AD 250, ca. AD 1350 and after AD 1700. These events correspond to phases of human settlement in the area. During 400–300 BC, the decline of deciduous trees, primarily Carpinus, coincided with an increase in indicators of human activity and fire frequency. At ca. AD 200, Carpinus and Tilia abundance decreased, corresponding to an increased importance of cereals (Secale and Triticum). Since ca. AD 1350, the impact of Teutonic settlement is apparent, and after AD 1700, deciduous forests largely disappeared.

The Interaction Between Forest Fires and Human Activity in Southern Switzerland

The impact of human activities on the fire regime in southern Switzerland was studied using (pre)historical charcoal and pollen data from lake sediments and statistical data from the 20th century. The cultural impact on forest fire was established by correlating charcoal-influx data with pollen percentages of anthropogenic indicators such as Plantago lanceolata, the Cerealia (sum of Avena t., Triticum t. and Hordeum t.) and Secale. During the 20th century, fire frequency was correlated with precipitation, dry and very dry periods and landscape management indicators. The effects of human activity on the fire regime are clearly recognisable since at least the Neolithic period. Using palaeoecological or statistical data, the variations in fire regime originating from anthropogenic actions may be differentiated from those due to climatic changes if they are sufficiently conspicuous.