Photosynthetic performance along a light gradient as related to leaf characteristics of a naturally occurring <Emphasis Type="Italic">Cypripedium flavum</Emphasis>

Photosynthesis, leaf structure, nitrogen content and nitrogen allocation in photosynthetic functions of Cypripedium flavum were studied in a naturally varying light regime. Light-saturated leaf net photosynthetic rate (A (max)) was strongly correlated with leaf dry mass per area (LMA), mesophyll conductance (g (m)) and area-based leaf nitrogen content (N(area)), with all variables increasing with increasing irradiance. Such coordinate variation of all these parameters illustrates the plastic response of leaf structure to high light (HL). Leaf N(area) was greater under HL than in low light (LL). The fractions of leaf nitrogen partitioning in carboxylation (P (R)) and bioenergetics (P (B)) were positively related to LMA. In contrast, P (R) and P (B) decreased with increasing mass-based leaf nitrogen content (N(mass)). However, no correlation was found between leaf nitrogen investment in light harvesting (P (L)) and either LMA or N(mass). Like maximum rate of carboxylation (V (cmax)) and electron transport (J (max)), the J (max)/V (cmax) ratio, which was strongly correlated to LMA, also increased significantly with irradiance. Under HL, leaf maximum photosynthetic nitrogen efficiency (ANUE) and intrinsic water use efficiency (WUE) were greater than in LL conditions, despite a small difference in WUE. This suggests that a functional balance in the photosynthetic machinery favors leaf photosynthetic plasticity of C. flavum in response to different light conditions. Given an ample soil nitrogen supply, C. flavum may offset its susceptibility to HL by efficient nitrogen use and higher stomatal and mesophyll conductance against photoinhibition so as to keep leaf photosynthesis positive.     

Response of carbon and nitrogen content in plants and soils to vegetation cover change in alpine Kobresia meadow of the source region of Lantsang, Yellow and Yangtze Rivers

We conducted this study in lightly and severely degraded Kobresia pygmaea meadow in Gande County, Qinghai Province of China. The purpose of this research was to compare carbon and nitrogen concentrations, content and dynamics of aboveground tissue, belowground roots and soil (0-40 cm) between lightly and severely degraded Kobresia meadow. The results showed that C and N concentrations and C:N ratio of the aboveground tissue were significantly higher in lightly degraded grassland than in severely degraded grassland. In addition, total carbon and nitrogen concentrations of the aboveground tissue were ranked in order of forbs > grasses > sedges in the same grassland type. Total carbon and nitrogen concentrations of belowground roots were significantly higher in severely degraded grassland than in lightly degraded grassland. Total carbon and nitrogen concentrations were higher in the aboveground tissue than in the belowground roots. Total soil organic carbon concentration in severely degraded grassland was significantly lower than that in lightly degraded grassland, and decreased with depth. C and N content per unit area was ranked in order of 0-40 cm soil depth > belowground roots > aboveground issue in the same grassland type. The total carbon content per unit area of aboveground tissue, roots and 0-40 cm soil depth declined by 7.60% after degradation from lightly (14669.2 g m⁻²) to severely degraded grassland (13554.3 g m⁻²), i.e., 0-40 cm soil depth declined by 4.10%, belowground roots declined by 59.97% and aboveground tissue declined by 15.39%. The nitrogen content per unit area of aboveground tissue, roots and 0-40 cm soil depth increased after degradation by 12.76% from lightly (3352.7 g m⁻²) to severely degraded grassland (3780.6 g m⁻²), i.e., 0-40 cm soil depth increased by 13.07%, belowground roots declined by 55.09% and aboveground tissue declined by 16.00%. As a result of grassland degradation, the total carbon lost by 11149 kg hm⁻², and the total nitrogen increased by 4278 kg hm⁻².     

Patterns in leaf traits of leguminous and non-leguminous dominant trees along a rainfall gradient in Ghana

Aims Both dominance distribution of species and the composition of the dominant species determine the distribution of traits within community. Leaf carbon (C) and nitrogen (N) isotopic composition are important leaf traits, and such traits of dominant species are associated with ecosystem C, water and N cycling. Very little is known how dominant species with distinct traits (e.g. N-fixing leguminous and non-leguminous trees) mediate resource utilization of the ecosystems in stressful environment.Methods Leaves of 81 dominant leguminous and non-leguminous trees were collected in forest (moist semi-deciduous and dry semi-deciduous ecosystems) and savanna (costal savanna, Guinean savanna and west Sudanian savanna ecosystems) areas and the transitional zone (between the forest and the savanna) along the transect from the south to the north of Ghana. We measured leaf traits, i.e. leaf δ 13 C, leaf δ 15 N, leaf water content, leaf mass per area (LMA) and C and N concentration. Correlation analyses were used to examine trait–trait relationships, and relationships of leaf traits with temperature and precipitation. We used analysis of covariance to test the differences in slopes of the linear regressions between legumes and non-legumes.Important findings Leaf δ 13 C, δ 15 N, leaf water content and LMA did not differ between leguminous and non-leguminous trees. Leaf N concentration and C:N ratio differed between the two groups. Moreover, leaf traits varied significantly among the six ecosystems. δ 13 C values were negatively correlated with annual precipitation and positively correlated with mean annual temperature. In contrast, leaf δ 15 N of non-leguminous trees were positively correlated with annual precipitation and negatively correlated with mean annual temperature. For leguminous trees, such correlations were not significant. We also found significant coordination between leaf traits. However, the slopes of the linear relationships were significantly different between leguminous and non-leguminous trees. Our results indicate that shifts in dominant trees with distinct water-use efficiency were corresponded to the rainfall gradient. Moreover, leguminous trees, those characterized with relative high water-use efficiency in the low rainfall ecosystems, were also corresponded to the relative high N use efficiency. The high proportion of leguminous trees in the savannas is crucial to mitigate nutrient stress.     

Association of protein-DNA recognition complexes: electrostatic and nonelectrostatic effects

In this study the electrostatic and nonelectrostatic contributions to the binding free energy of a number of different protein-DNA recognition complexes are investigated. To determine the electrostatic effects in the protein-DNA association the Poisson-Boltzmann approach was applied. Overall the salt-dependent electrostatic free energy opposed binding in all protein-DNA complexes except one, and the salt-independent electrostatic contribution favored binding in more than half of the complexes. Further the salt-dependent electrostatic free energy increased with higher ionic concentrations and therefore complex association is stronger opposed at higher ionic concentrations. The hydrophobic effect in the protein-DNA complexes was determined from the buried accessible surface area and the surface tension. A majority of the complexes showed more polar than nonpolar buried accessible surface area. Interestingly the buried DNA-accessible surface area was preferentially hydrophilic, only in one complex a slightly more hydrophobic buried accessible surface area was observed. A quite sophisticated balance between several different free energy components seems to be responsible for determining the free energy of binding in protein-DNA systems.     

In vitro proliferation of blood,spleen and thymus leukocytes from the turtle Mauremys caspica

Cell-mediated immune responses is commonly evaluated by cell proliferation assays. Mitogens are known to induce a vigorous proliferative response in lymphoid cells from mammals but relatively fewer studies have investigated mitogen-mediated lymphoproliferation in non-mammalian animals. In the present work, we incubated spleen, thymus and blood leukocytes with phytohaemagglutinin (PHA), concanavalin A (Con A), lipopolysaccharide (LPS) and pokeweed mitogen (PWM), by different times of incubation (96 and 120 h) and at different concentrations. Our results show that the optimal mitogen concentrations inducing proliferation on leukocytes from Mauremys caspica were 20 microg/ml PHA, 1 microg/ml Con A, 12.5 microg/ml LPS and 1/150 dilution PWM. The optimal time of incubation was dependent on the type of leukocytes (peripheral blood leukocytes, splenic leukocytes or thymic cells) and the mitogen utilized.     

Independent tyrosyl contributions to the CD of Ff gene 5 protein and the distinctive effects of Y41H and Y41F mutants on protein-protein cooperative interactions

The gene 5 protein (g5p) of the Ff virus contains five Tyr, individual mutants of which have now all been characterized by CD spectroscopy. The protein has a dominant tyrosyl 229-nm L(a) CD band that is shown to be approximately the sum of the five individual Tyr contributions. Tyr41 is particularly important in contributing to the high cooperativity with which the g5p binds to ssDNA, and Y41F and Y41H mutants are known to differ in dimer-dimer packing interactions in crystal structures. We compared the solution structures and binding properties of the Y41F and Y41H mutants using CD spectroscopy. Secondary structures of the mutants were similar by CD analyses and close to those derived from the crystal structures. However, there were significant differences in the binding properties of the two mutant proteins. The Y41H protein had an especially low binding affinity and perturbed the spectrum of poly[d(A)] in 2 mM Na(+) much less than did Y41F and the wild-type gene 5 proteins. Moreover, a change in the Tyr 229 nm band, assigned to the perturbation of Tyr34 at the dimer-dimer interface, was absent in titrations with the Y41H mutant under low salt conditions. In contrast, titrations with the Y41H mutant in 50 mM Na(+) exhibited typical CD changes of both the nucleic acid and the Tyr 229-nm band. Thus, protein-protein and g5p-ssDNA interactions appeared to be mutually influenced by ionic strength, indicative of correlated changes in the ssDNA binding and cooperativity loops of the protein or of indirect structural constraints.     

Estimating allelic richness: effects of sample size and bottlenecks

Although differences in sampling intensity can bias comparisons of allelic richness (A) among populations, investigators often fail to correct estimates of A for differences in sample size. Methods that standardize A on the basis of the size of the smallest number of samples in a comparison are preferable to other approaches. Rarefaction and repeated random subsampling provide unbiased estimates of A with the greatest precision and thus provide greatest statistical power to detect differences in variation. Less promising approaches, in terms of bias or precision, include single random subsampling, eliminating very small samples, using sample size as a covariate or extrapolating estimates obtained from small samples to a larger number of individuals.     

The Arabidopsis phenylalanine ammonia lyase gene family: kinetic characterization of the four PAL isoforms

In Arabidopsis thaliana, four genes have been annotated as provisionally encoding PAL. In this study, recombinant native AtPAL1, 2, and 4 were demonstrated to be catalytically competent for l-phenylalanine deamination, whereas AtPAL3, obtained as a N-terminal His-tagged protein, was of very low activity and only detectable at high substrate concentrations. All four PALs displayed similar pH optima, but not temperature optima; AtPAL3 had a lower temperature optimum than the other three isoforms. AtPAL1, 2 and 4 had similar K(m) values (64-71 microM) for l-Phe, with AtPAL2 apparently being slightly more catalytically efficacious due to decreased K(m) and higher k(cat) values, relative to the others. As anticipated, PAL activities with l-tyrosine were either low (AtPAL1, 2, and 4) or undetectable (AtPAL3), thereby establishing that l-Phe is the true physiological substrate. This detailed knowledge of the kinetic and functional properties of the various PAL isoforms now provides the necessary biochemical foundation required for the systematic investigation and dissection of the organization of the PAL metabolic network/gene circuitry involved in numerous aspects of phenylpropanoid metabolism in A. thaliana spanning various cell types, tissues and organs.     

Intra-inflorescence variation in floral traits and reproductive success of the hermaphrodite Silene acutifolia

BACKGROUND AND AIMS: Intraspecific variation in floral components and reproductive success is often located at the intra-individual level. The arrangement of flowers within inflorescences may explain a great deal of this variation. The variation in number of ovules, fruit set, number of seeds per fruit, seed set, seed weight and seed germination is investigated at different positions within the inflorescence of Silene acutifolia. METHODS: Data were obtained in natural populations, and germination experiments were conducted in a germination chamber. KEY RESULTS: The number of ovules, fruit set, number of seeds, seed set and seed weight, showed a significant decline from early (primary) position to later (tertiary) position. The patterns of intra-inflorescence variation were consistent in different populations and years of study. Seed germination showed an opposite pattern, seeds from primary position showed the lowest germination percentages and seeds from tertiary position the highest, although the effect of position on germination was only marginally significant. There was significant among-population variation in number of ovules per flower. Fruit set also varied significantly among populations, with lower fruit set in the smaller and more isolated population. No significant among-population differences were detected in number of seeds per fruit and seed set. Seeds from the smallest and more isolated population (Arnado) were the lightest. Seed germination showed strong differences between populations, seeds from Arnado started to germinate later, and showed the lowest final germination percentages. CONCLUSIONS: Architectural effects or resource competition are the most commonly proposed hypothesis to explain these patterns. Data suggest that there is less pollen available to pollinate tertiary flowers, and that there is not enough outcross pollen in Arnado. The germination percentages suggest that there is variation in the source of pollen within inflorescences, with high probability of receiving outcross pollen in flowers from primary position, and higher probability of geitonogamous crosses in tertiary flowers.