Carbon and nitrogen isotope ratios in different compartments of a healthy and a declining Picea abies forest in the Fichtelgebirge,NE Bavaria

Summary Natural carbon and nitrogen isotope ratios were measured in different compartments (needles and twigs of different ages and crown positions, litter, understorey vegetation, roots and soils of different horizons) on 5 plots of a healthy and on 8 plots of a declining Norway spruce (Picea abies (L.) Karst.) forest in the Fichtelgebirge (NE Bavaria, Germany), which has recently been described in detail (Oren et al. 1988a; Schulze et al. 1989). The ¹³C values of needles did not differ between sites or change consistently with needle age, but did decrease from the sun-to the shade-crown. This result confirms earlier conclusions from gas exchange measurements that gaseous air pollutants did no long-lasting damage in an area where such damage was expected. Twigs (¹³C between-25.3 and-27.8) were significantly less depleted in ¹³C than needles (¹³C between-27.3 and-29.1), and ¹³C in twigs increased consistently with age. The ¹⁵N values of needles ranged between-2.5 and-4.1 and varied according to stand and age. In young needles ¹⁵N decreased with needle age, but remained constant or increased in needles that were 2 or 3 years old. Needles from the healthy site were more depleted in ¹⁵N than those from the declining site. The difference between sites was greater in old needles than in young ones. This differentiation presumably reflects an earlier onset of nitrogen reallocation in needles of the declining stand. ¹⁵N values in twigs were more negative than in needles (-3.5 to-5.2) and showed age- and stand-dependent trends that were similar to the needles. ¹⁵N values of roots and soil samples increased at both stands with soil depth from-3.5 in the organic layer to +4 in the mineral soil. The ¹⁵N values of roots from the mineral soil were different from those of twigs and needles. Roots from the shallower organic layer had values similar to twigs and needles. Thus, the bulk of the assimilated nitrogen was presumably taken up by the roots from the organic layer. The problem of separation of ammonium or nitrate use by roots from different soil horizons is discussed.     

Carbon and nitrogen partitioning in the biennial monocarp Arctium tomentosum Mill

Summary Growth and nitrogen partitioning were investigated in the biennial monocarp Arctium tomentosum in the field, in plants growing at natural light conditions, in plants in which approximately half the leaf area was removed and in plants growing under 20% of incident irradiation. Growth quantities were derived from splined cubic polynomial exponential functions fitted to dry matter, leaf area and nitrogen data.Main emphasis was made to understanding of the significance of carbohydrate and nitrogen storage of a large tuber during a 2-years' life cycle, especially the effect of storage on biomass and seed yield in the second season. Biomass partitioning favours growth of leaves in the first year rosette stage. Roots store carbohydrates at a constant rate and increase storage of carbohydrates and nitrogen when the leaves decay at the end of the first season. In the second season the reallocation of carbohydrates from storage is relatively small, but reallocation of nitrogen is very large. Carbohydrate storage just primes the growth of the first leaves in the early growing season, nitrogen storage contributes 20% to the total nitrogen requirement during the 2nd season. The efficiency of carbohydrate storage for conversion into new biomass is about 40%. Nitrogen is reallocated 3 times in the second year, namely from the tuber to rosette leaves and further to flower stem leaves and eventually into seeds. The harvest index for nitrogen is 0.73, whereas for biomass it is only 0.19.     

Control of the rate of cell enlargement: Excision,wall relaxation,and growth-induced water potentials

A new guillotine thermocouple psychrometer was used to make continuous measurements of water potential before and after the excision of elongating and mature regions of darkgrown soybean (Glycine max L. Merr.) stems. Transpiration could not occur, but growth took place during the measurement if the tissue was intact. Tests showed that the instrument measured the average water potential of the sampled tissue and responded rapidly to changes in water potential. By measuring tissue osmotic potential ( _s ), turgor pressure ( _p ) could be calculated. In the intact plant, _s and _p were essentially constant for the entire 22 h measurement, but _s was lower and _p higher in the elongating region than in the mature region. This caused the water potential in the elongating region to be lower than in the mature region. The mature tissue equilibrated with the water potential of the xylem. Therefore, the difference in water potential between mature and elongating tissue represented a difference between the xylem and the elongating region, reflecting a water potential gradient from the xylem to the epidermis that was involved in supplying water for elongation. When mature tissue was excised with the guillotine, _s and _p did not change. However, when elongating tissue was excised, water was absorbed from the xylem, whose water potential decreased. This collapsed the gradient and prevented further water uptake. Tissue _p then decreased rapidly (5 min) by about 0.1 MPa in the elongating tissue. The _p decreased because the cell walls relaxed as extension, caused by _p , continued briefly without water uptake. The _p decreased until the minimum for wall extension (Y) was reached, whereupon elongation ceased. This was followed by a slow further decrease in Y but no additional elongation. In elongating tissue excised with mature tissue attached, there was almost no effect on water potential or _p for several hours. Nevertheless, growth was reduced immediately and continued at a decreasing rate. In this case, the mature tissue supplied water to the elongating tissue and the cell walls did not relax. Based on these measurements, a theory is presented for simultaneously evaluating the effects of water supply and water demand associated with growth. Because wall relaxation measured with the psychrometer provided a new method for determining Y and wall extensibility, all the factors required by the theory could be evaluated for the first time in a single sample. The analysis showed that water uptake and wall extension co-limited elongation in soybean stems under our conditions. This co-limitation explains why elongation responded immediately to a decrease in the water potential of the xylem and why excision with attached mature tissue caused an immediate decrease in growth rate without an immediate change in _p Abbreviations and symbols L tissue conductance for water - m wall extensibility - Y average yield threshold (MPa) - _o water potential of the xylem - _p turgor pressure - _s osmotic potential - _w water potential of the elon gating tissue     

Ultrasonic radiation induced lipid peroxidation in liposomal membrane

Summary Ultrasonic radiation produced a dose dependent linear increase in lipid peroxidation (MDA formation) in the liposomal membrane. The yield of MDA was significantly inhibited by butylated hydroxytoluene (BHT), the antioxidant, sodium formate, the OH radical scavenger, and EDTA, the metal ion chelator. Ascorbic acid at low concentration increased the ultrasonic induced MDA formation while high concentrations inhibited lipid peroxidation. A mechanism of ultrasound induced lipid peroxidation is suggested.     

Computer-aided three-dimensional reconstructions of the arrangement of primary spermatocytes in human seminiferous tubules

Summary With the use of a digital image-processing method three-dimensional reconstructions of the arrangement of spermatocytes in human seminiferous tubules were performed. With this method it was possible to investigate the cellular distribution in the tubule in nearly any given perspective and projection. In addition, by means of simple mathematical procedures, such as by transformation of Cartesian coordinates into cylindrical coordinates, it was possible to vary the shape of a reconstruction, i.e., to convert the cylindrical image of a tubular portion into a right-angled r--z-representation.The present work not only confirms the existence of a complex helical plan of organization of the human seminiferous epithelium but also provides further aspects of the phenomenon of physiological germ-cell loss and its integration into the kinetics of spermatogenesis.Dedicated to Prof. E.C. Roosen-Runge, Seattle, on the occasion of his 75th birthday     

The importance of the Escherichia coli ribosomal protein L16 for the reconstitution of the peptidyl-tRNA hydrolysis activity of peptide chain termination

The incubation of the 50 S ribosomal subunit of Escherichia coli with 1.5 M LiCl yields 1.5c core particles inactive in the peptidyl-tRNA hydrolysis activity of in vitro termination. The omission of L16 alone from reconstitutions of the proteins into the core results in inactive ribosomes. The single omission of a number of other proteins, in particular L7/L12, L10, L25, L27, and L15, gives ribosomes with intermediate activity. L16 alone is unable to restore significant activity to 1.5c cores, but together L16 and the above "stimulating" proteins produce particles as active as those reconstituted with the full complement of proteins. The ribosomal proteins important for the expression of peptidyl-tRNA hydrolysis and peptidyl transferase activities are very similar. However, ribosomes lacking both L11 and L16, but not L16 alone, surprisingly can catalyze codon- and release factor 2-dependent peptidyl-tRNA hydrolysis. The addition of L16 dramatically increases the activity. L16 is, therefore, important but not essential for the expression of the release factor 2-dependent peptidyl-tRNA hydrolysis.     

Contribution to the study on the reparative effect of exogenous DNA in the irradiated meristem ofVicia faba

The present report is focused on the study of participation of exogenous DNA in the process of postirradiation reparation of meristematic cells ofVicia faba primary roots. It is aimed at comparison of the positive reparative effect of isologous DNA with postirradiation action of heterologous DNA in its native, thermally denatured and DNAase-degraded forms, or DNA degraded by ultrasound, and with the effect of other biologically important macromolecules (RNA, histone, heparin, and dextran sulphate). For this purpose, the roots ofVicia faba irradiated by 150 r exposure were cultivated in solutions containing the above substances for an appropriate time interval. In squash slides both mitotic activity of the investigated cell population and frequency of postmetaphase chromosomal aberrations induced by radiation were evaluated. It was shown that a stimulation of cell division and reparation of chromosome damages were supported exclusively by isologous DNA. On the contrary, exogenously applied heterologous DNA increased postirradiation frequency of aberrations; maintenance of native structure of applied DNA was an essential condition for the above effect. Other macromolecules investigated on the course of postirradiation reparation ofVicia faba meristematic cells were without effect.     

Influence of light and darkness on the concentration of lactic,glycolic, succinic,malic and citric acid in pea plants

Chromatographic separation of an extract of organic acids on a Dowex-l column in the formiate cycle was used to study the content of several organic acids in pea plants, cultivated either in light or in darkness. Concentration changes of the individual acids in the course of growth indicate that the citrate cycle is blocked in the cotyledons of plants grown in light in the period around the 15th day of growth, probably at the site of succinic dehydrogenase (succinic and lactic acids accumulate and the content of citric and malic acids is exhausted). There is no inhibition in the cotyledons of etiolated plants. In vegetative organs, the concentration of the majority of the acids studied is lower than in cotyledons, probably because synthetic processes prevail over degradation processes in these organs. It seems that other processes besides the citrate cycle participate in malate synthesis in pea plants.     

Influence of exogenous DNA on Ypenyl-treated chromosomes ofVicia faba L.

This paper is a study of the effect of exogenous DNA of different genetic origins on the repair of meristematic cells of primary roots ofVicia faba, damaged by 24 hour treatment with 0·01mm solution of Ypenyl. Both kinds of DNA,i.e. isologous and heterologous, stimulated cell proliferation which was decreased by the action of the radiomimetic and influenced both dynamics of production of chromosome aberrations and the interchromosomal distribution of induced damage. While heterologous DNA increased the frequency of aberrations after all recovery periods studied, isologous DNA significantly decreased the number of chromosomal aberrations. Heterologous DNA increased at the same time the relative number of breaks in the group of small chromosomes, while by the action of isologous DNA the number of aberrations related to this group of chromosomes was relatively decreased.