The Effect of Soil Compaction on Differentiation of Late Metaxylem in Common Bean (Phaseolus vulgaris L.)

Recent studies among several plant species have shown that maturationof the largest vessels in primary xylem of roots occurs muchlater than is commonly assumed. These results have importantimplications for studies of water and nutrient uptake sincethe condition of the vessels, termed late metaxylem (LMX), mighthave a large effect on the potential conductivity of the xylem.To determine whether this phenomenon occurred in common bean(Phaseolus vulgaris L.), patterns of root xylem differentiationwere studied in young bean plants. Soil bulk density was variedin one trial to determine whether differentiation of LMX wassensitive to the growing medium. Vessels of LMX lost cell contentsand-became functional conduits between 100 and 150 mm from theroot apex. Increasing soil bulk density caused the zone of maturationof LMX to shift toward the root apex, but this zone was nevercloser than 67 mm. In the region where the primary root increasedin diameter as it merged with the hypocotyl, a zone was foundwhere vessels increased in number, had a reduced diameter, andwere arranged in a ring, the normal tetrarch arrangement ofthe xylem being lost. Potential conductivity in this zone wasconsiderably less than in zones with conventional large LMXvessels, so the zone appears to present an important restrictionto water transport from the root to the shoot. Thus, while thephenomenon of late maturation of LMX occurs in common bean,its significance in transport of water from roots to shootsis unclear Phaseolus vulgaris L., common bean, metaxylem, soil compaction, roots, anatomy     

Plastid terminal oxidase (PTOX) has the potential to act as a safety valve for excess excitation energy in the alpine plant species Ranunculus glacialis L.

Ranunculus glacialis leaves were tested for their plastid terminal oxidase (PTOX) content and electron flow to photorespiration and to alternative acceptors. In shade‐leaves, the PTOX and NAD(P)H dehydrogenase (NDH) content were markedly lower than in sun‐leaves. Carbon assimilation/light and C_i response curves were not different in sun‐ and shade‐leaves, but photosynthetic capacity was the highest in sun‐leaves. Based on calculation of the apparent specificity factor of ribulose 1·5‐bisphosphate carboxylase/oxygenase (Rubisco), the magnitude of alternative electron flow unrelated to carboxylation and oxygenation of Rubisco correlated to the PTOX content in sun‐, shade‐ and growth chamber‐leaves. Similarly, fluorescence induction kinetics indicated more complete and more rapid reoxidation of the plastoquinone (PQ) pool in sun‐ than in shade‐leaves. Blocking electron flow to assimilation, photorespiration and the Mehler reaction with appropriate inhibitors showed that sun‐leaves were able to maintain higher electron flow and PQ oxidation. The results suggest that PTOX can act as a safety valve in R. glacialis leaves under conditions where incident photon flux density (PFD) exceeds the growth PFD and under conditions where the plastoquinone pool is highly reduced. Such conditions can occur frequently in alpine climates due to rapid light and temperature changes.     

Time course of nodule development in the Discaria trinervis (Rhamnaceae) –Frankia symbiosis

The time course of initiation and development of root nodules was investigated in the South American actinorhizal shrub Discaria trinervis (Rhamnaceae). A local strain of Frankia (BCU110501) which was isolated from D. trinervis nodules, was used as inoculum. Inoculated seedlings were periodically studied under the light microscope after clearing with aqueous NaClO. In parallel, semithin and ultrathin sections were analysed by light and electron microscopy. Infection by Frankia BCU110501 involved intercellular penetration among epidermal and cortical root cells. Nodule primordia were detected from 6 d after inoculation, while bacteria were progressing through intercellular spaces of the outer layers of cortical cells. Invasion of host cells by the symbiont occurred 7–9 d after inoculation, and hypertrophy of the primordium cells was associated with Frankia penetration. Root hairs were not deformed during the early events of nodule formation. From 13 to 16 d after inoculation, the proximal cellular zone of the primordia behaved differently from the other tissues after NaClO treatment and remained darkly pigmented. At the same time, differentiation of Frankia vesicles started to occur inside already infected cells. By 16 d after inoculation, spherical vesicles of BCU110501 were homogeneously distributed in the host cells. These vesicles were septate and surrounded by void space. Frankia spores or sporangia were not observed in the nodule tissue. This study has clarified the mode of Frankia penetration in D. trinervis , one of the Rhamnaceae which also includes Ceanothus . The events involved in infection, nodule induction, host-cell infection and vesicle differentiation have been characterized and identified as time-segregated developmental processes in the ontogeny of D. trinervis root nodules.     

A new Pyrenean hybrid Cirsium (Asteraceae) as revealed by morphological and molecular analyses

A new nothosubspecies Cirsium  ×  vivantii is described after a molecular and morphological characterization of eight individuals collected in two separate valleys of the French central Pyrenees. Both hypervariable Amplified Fragment Length Polymorphism (AFLP) markers and nuclear rDNA (ITS) and plastid ( trn L-F, TRNT-L) DNA sequences were analysed. The profiles of these hybrid samples were compared to those of 43 individuals belonging to their presumed parental taxa C. carniolicum ssp. rufescens and C. palustre . A total of 133 AFLP bands were scored from three primer-pair combinations. All 130 AFLP bands that amplified in the hybrid samples were present in either C. carniolicum ssp. rufescens , C. palustre or both taxa, supporting the participation of these plant genomes in the resulting hybrids. Several Additive Polymorphic Sites (APS) detected in the ITS sequences of the hybrid samples also confirmed their derived origins from ribotypes of the two parental taxa. The lack of exclusive AFLP markers and the nonconcerted evolution of rDNA polymorphisms towards either of the parental ribotypes indicated their recent origin. Plastid trn T-L sequences were used to identify C. palustre as the maternal parent of six of these hybrid individuals; either parent could have acted as the plastid genome donor for the other two individuals. The morphological study revealed that all hybrid individuals were morphologically intermediate between their parents showing largely lobed and less spiny basal leaves as in C. carniolicum ssp. rufescens and decurrent leaf bases and pinkish corollas as in C. palustre .  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 154 , 421–434.     

Leaf stomatal responses to vapour pressure deficit under current and CO2-enriched atmosphere explained by the economics of gas exchange

Using the economics of gas exchange, early studies derived an expression of stomatal conductance ( g ) assuming that water cost per unit carbon is constant as the daily loss of water in transpiration ( f _e) is minimized for a given gain in photosynthesis ( f _c). Other studies reached identical results, yet assumed different forms for the underlying functions and defined the daily cost parameter as carbon cost per unit water. We demonstrated that the solution can be recovered when optimization is formulated at time scales commensurate with the response time of g to environmental stimuli. The optimization theory produced three emergent gas exchange responses that are consistent with observed behaviour: (1) the sensitivity of g to vapour pressure deficit ( D ) is similar to that obtained from a previous synthesis of more than 40 species showing g to scale as 1 −  m  log( D ), where m   ∈  [0.5,0.6], (2) the theory is consistent with the onset of an apparent 'feed-forward' mechanism in g , and (3) the emergent non-linear relationship between the ratio of intercellular to atmospheric [CO₂] ( c _i/ c _a) and D agrees with the results available on this response. We extended the theory to diagnosing experimental results on the sensitivity of g to D under varying c _a.     

Cladoceran birth and death rates estimates: experimental comparisons of egg-ratio methods

I. Birth and death rates of natural cladoceran populations cannot be measured directly. Estimates of these population parameters must be calculated using methods that make assumptions about the form of population growth. These methods generally assume that the population has a stable age distribution.
2. To assess the effect of variable age distributions, we tested six egg ratio methods for estimating birth and death rates with data from thirty-seven laboratory populations of Daphnia pulicaria. The populations were grown under constant conditions, but the initial age distributions and egg ratios of the populations varied. Actual death rates were virtually zero, so the difference between the estimated and actual death rates measured the error in both birth and death rate estimates.
3. The results demonstrate that unstable population structures may produce large errors in the birth and death rates estimated by any of these methods. Among the methods tested, Taylor and Slatkin's formula and Paloheimo's formula were most reliable for the experimental data.
4. Further analyses of three of the methods were made using computer simulations of growth of age-structured populations with initially unstable age distributions. These analyses show that the time interval between sampling strongly influences the reliability of birth and death rate estimates. At a sampling interval of 2.5 days (equal to the duration of the egg stage), Paloheimo's formula was most accurate. At longer intervals (7.5–10 days), Taylor and Slatkin's formula which includes information on population structure was most accurate.     

Ecological differentiation between the Sardinian endemic Maniola nurag and the pan-European M. jurtina

Recently refined evolutionary theories have highlighted that ecological interactions and environmental gradients can play a major role in speciation. This paper reports on a 3‐year field study, in which the ecology of two congeneric butterfly species was used to explore and compare the environmental factors determining their spatial distribution. These data are discussed in the context of possible speciation scenarios between the Sardinian populations of Maniola nurag and M. jurtina. M. nurag is endemic to the island of Sardinia, while M. jurtina is widespread over Europe. In Sardinia, the two species are locally sympatric. Mark–release–recapture experiments were combined with measures of environmental variables in 15 1‐ha plots, established in areas of potential habitat for the butterflies. Constrained linear models were parameterized from mark–recapture data to estimate both individual (survival and capture probabilities) and population (population size and recruitment) parameters. The two species had similar demography, movement patterns, life history, and behaviour. Population sizes developed in a parabolic fashion from beginning to end of the flight season. Differences included local population size, adult phenology, and habitat requirements. Long‐distance movements larger than 1.5 km were observed, suggesting a substantial amount of gene‐flow between populations of the endemic as well as the widespread species. Multivariate analyses revealed four main environmental gradients responsible for the abundance of the butterflies in an area. Both species responded similarly to environmental variables. However, each species’s abundance was correlated with a different environmental gradient determined by vegetation cover and structure. When sympatric, the two species responded to subtle differences in microhabitat structure. This might originally have induced their divergence. This study is an example of how empirical field data on population dynamics, dispersal, and habitat characteristics of two sympatric congeners can further our understanding of how species differentiate despite existing gene‐flow. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 89 , 561–574.     

Polydomy in ants: what we know, what we think we know, and what remains to be done

The correct identification of colony boundaries is an essential prerequisite for empirical studies of ant behaviour and evolution. Ant colonies function at various organizational levels, and these boundaries may be difficult to assess. Moreover, new complexity can be generated through the presence of spatially discrete subgroups within a more or less genetically homogeneous colony, a situation called polydomy. A colony is polydomous only if individuals (workers and brood) of its constituent nests function as a social and cooperative unit and are regularly interchanged among nests. This condition was previously called polycalic, and the term polydomy was used in a broader sense for a group of daughter nests of the same mother colony (implying limited female dispersal), without regard to whether these different nests continued to exchange individuals. We think that this distinction between ‘polycaly’ and ‘polydomy’ concerns two disparate concepts. We thus prefer the narrower definition of polydomy, which groups individuals that interact socially. Does this new level of organization affect the way in which natural selection acts on social traits? Here, after examining the history of terms, we review all ant species that have been described as expressing polydomous structures. We show that there is no particular syndrome of traits predictably associated with polydomy. We detail the existing theoretical predictions and empirical results on the ecology of polydomy, and the impact of polydomy on social evolution and investment strategies, while carefully distinguishing monogynous from polygynous species. Finally, we propose a methodology for future studies and offer ideas about what remains to be done. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90 , 319–348.