Cyanide metabolism in relation to ethylene production in plant tissues

HCN is the putative product of C-1 and amino moieties of 1-aminocyclopropane-1-carboxylic acid (ACC) during its conversion to ethylene. In apple (Malus sylvestrus Mill.) slices or auxin-treated mungbean (Vigna radiata L.) hypocotyls, which produced ethylene at high rates, the steady state concentration of HCN was found to be no higher than 0.2 micromolar, which was too low to inhibit respiration (reported Ki for HCN to inhibit respiration was 10-20 micromolar). However, these tissues became cyanogenic when treated with ACC, the precursor of ethylene, and with 2-aminoxyacetic acid, which inhibits β-cyanoalanine synthase, the main enzyme to detoxify HCN; the HCN levels in these tissues went up to 1.7 and 8.1 micromolar, respectively. Although ethylene production by avocado (Persea gratissima) and apple fruits increased several hundred-fold during ripening, β-cyanoalanine synthase activity increased only one- to two-fold. These findings support the notion that HCN is a co-product of ethylene biosynthesis and that the plant tissues possess ample capacity to detoxify HCN formed during ethylene biosynthesis so that the concentration of HCN in plant tissues is kept at a low level.     

Flower production in relation to individual plant age and leaf production among different patches of Corydalis intermedia

The life history of an organism can be viewed as the combination of allocations made to maintenance, growth, and reproduction. Allocation to these functions are constrained by trade-offs as increased investment to one function may happen at the expense of another. Moreover, because fecundity and survival probabilities are affected by both the state of an individual and by its surrounding environment, optimal allocation to reproduction and growth may vary with both individual size/age and with the habitat in which it lives. In this study we aim to describe how flower production varies with individual plant age and leaf production among different patches of the perennial herb Corydalis intermedia. We take advantage of the construction of the underground storage organ to estimate the age of individual plants which allows us tacitly to relate flower and leaf production to individual age and successional status of the patch. We sampled all individuals present in nine patches from the same forest and estimated their age, flower production and total leaf area. The age distributions showed that each patch was most often dominated by a few and consecutive age classes. In patches where individuals had the oldest mean age, very few or no juvenile age classes were found suggesting that recruitment had ceased. Based on the age distribution of the patches we propose that the dynamics may best be described as metapopulational with colonization of newly formed open forest gaps and a successionally determined extinction as the patch gradually becomes too shaded for recruitment. Both mean flower production, leaf area and age varied significantly among patches. Flower production increased with both increasing age and leaf area. We found no indication of a trade off between reproduction and vegetative growth since flower production showed a positive relation with leaf production even after removing the effect of age. Number of flowers produced by plants of the same age but growing in different patches did not vary indicating that the difference among patches mainly was due to a difference in age distribution. No individuals produced flowers before they reached an estimated age of three years. Production of flowers followed a power function with increasing age. Our data suggests that C. intermedia plants change their allocation strategy with age investing a relatively large amount of energy in flower production immediately after the immature growth phase when recruitment in their patch may be high. Production of flowers then reaches a plateau around the age of 11 years after which number of flowers produced stays constant. This revised version was published online in June 2006 with corrections to the Cover Date.     

Proteins involved in the production and perception of oligosaccharides in relation to plant and animal development.

Chitin oligosaccharides and their derivatives are involved in developmental and defence-related signalling pathways. Major advances include the structural identification of lectins involved in development that bind chitin oligosaccharides and the links between chitin oligosaccharide and hyaluronan synthesis. Also, recent advances in the understanding of the biological role of oligosaccharides are summarised in a model for multistep glycan recognition.     

Variation of nectar production in relation to plant characteristics in protandrous Aconitum gymnandrum

Aims Floral nectar plays a vital role in plant reproductive success by attracting pollinators. Nectar traits of a flower can depend directly on plant characteristics other than environmental factors and exhibit extensive flower- and plant-level variations. Studies on nectar traits frequently focused on intraplant variation for dichogamous plants, but few have paid attention to both intra- and interplant nectar variations in relation to plant characteristics. Revealing within- and among-plant variation and its relative magnitude is important for our understanding of how pollinator-mediated selection can act on nectar traits and evolution of nectar traits.Methods Through investigating protandrous Aconitum gymnandrum populations at the Alpine Meadows and Wetland Ecosystems Research Station of Lanzhou University, we examined the relationships between nectar production per flower and plant characteristics (e.g. flower position within inflorescences, floral sexual phases, flowering time, inflorescence size and floral attractive traits).Important findings A. gymnandrum exhibited a declining gradient in the nectar volume along inflorescences, with more nectar in basal flowers than distal ones. Protandrous flowers of A. gymnandrum did not show gender-biased nectar production while the nectar volume varied with different stages of floral sexual phases. The significant correlation between the first flowering date of individuals and the mean nectar volume per flower was positive in 2013, but became negative in 2014, suggesting complex effects of biotic and abiotic factors. The mean nectar volume per flower was not related to inflorescence size (the number of total flowers per plant). Furthermore, nectar production was weakly associated with floral attractive traits (the petal width and the galea height), even if the effect of flowering time of individuals was removed, suggesting that the honesty of floral traits as signals of nectar reward for pollinators is not stable in this species.     

Forest structure,diversity, and primary production in relation to disturbance severity

1. Differential disturbance severity effects on forest vegetation structure, species diversity, and net primary production (NPP) have been long theorized and observed. Here, we examined these factors concurrently to explore the potential for a mechanistic pathway linking disturbance severity, changes in light environment, leaf functional response, and wood NPP in a temperate hardwood forest.
2. Using a suite of measurements spanning an experimental gradient of tree mortality, we evaluated the direction and magnitude of change in vegetation structural and diversity indexes in relation to wood NPP. Informed by prior observations, we hypothesized that forest structural and species diversity changes and wood NPP would exhibit either a linear, unimodal, or threshold response in relation to disturbance severity. We expected increasing disturbance severity would progressively shift subcanopy light availability and leaf traits, thereby coupling structural and species diversity changes with primary production.
3. Linear or unimodal changes in three of four vegetation structural indexes were observed across the gradient in disturbance severity. However, disturbance‐related changes in vegetation structure were not consistently correlated with shifts in light environment, leaf traits, and wood NPP. Species diversity indexes did not change in response to rising disturbance severity.
4. We conclude that, in our study system, the sensitivity of wood NPP to rising disturbance severity is generally tied to changing vegetation structure but not species diversity. Changes in vegetation structure are inconsistently coupled with light environment and leaf traits, resulting in mixed support for our hypothesized cascade linking disturbance severity to wood NPP.

     

Rhizosphere microbial community structure in relation to root location and plant iron nutritional status

Root exudate composition and quantity vary in relation to plant nutritional status, but the impact of the differences on rhizosphere microbial communities is not known. To examine this question, we performed an experiment with barley (Hordeum vulgare) plants under iron-limiting and iron-sufficient growth conditions. Plants were grown in an iron-limiting soil in root box microcosms. One-half of the plants were treated with foliar iron every day to inhibit phytosiderophore production and to alter root exudate composition. After 30 days, the bacterial communities associated with different root zones, including the primary root tips, nonelongating secondary root tips, sites of lateral root emergence, and older roots distal from the tip, were characterized by using 16S ribosomal DNA (rDNA) fingerprints generated by PCR-denaturing gradient gel electrophoresis (DGGE). Our results showed that the microbial communities associated with the different root locations produced many common 16S rDNA bands but that the communities could be distinguished by using correspondence analysis. Approximately 40% of the variation between communities could be attributed to plant iron nutritional status. A sequence analysis of clones generated from a single 16S rDNA band obtained at all of the root locations revealed that there were taxonomically different species in the same band, suggesting that the resolving power of DGGE for characterization of community structure at the species level is limited. Our results suggest that the bacterial communities in the rhizosphere are substantially different in different root zones and that a rhizosphere community may be altered by changes in root exudate composition caused by changes in plant iron nutritional status.     

长白山苔原草本植物入侵与土壤环境的关系

在对长白山高山苔原西坡样带内132个样方进行植被调查和土壤取样分析的基础上,应用冗余分析(RDA)和典型相关分析方法,探讨了草本植物入侵苔原带程度与苔原土理化性质及环境之间的关系。研究表明,长白山苔原带西坡草本入侵程度区域差异明显,可分为5个不同的入侵等级;海拔、坡度、全钾含量、粘粒含量、有机质含量等10种土壤环境因子与草本植物入侵程度明显相关。RDA分析表明土壤环境因子能解释93%的植物物种多度信息,影响草本植物入侵的主要土壤因子是有机质含量,粘粒含量和坡度;第一对典型变量说明有机质含量与牛皮杜鹃多度正相关,与大白花地榆多度负相关,粘粒含量则相反;第二对典型变量说明海拔、速效氮含量与笃斯越桔、长白老鹳草多度呈负相关。长白山苔原带西坡草本植物在空间分布上是离散的,呈斑块状。可见,草本植物入侵,对生境是有所选择的。土壤有机质含量与灌木多度呈正相关,说明在草本入侵过程中,土壤有机质含量会减少;或者有机质含量减少的地方,灌木生长退化,草本由此开始侵入定植。     

Distribution of plant functional attributes in a managed forest in relation to neighbourhood structure

The importance of neighbourhood structure on the distribution of plant functional attributes was investigated in two managed forests in Denmark. Species composition was recorded for 325 plots of 5×5 m and species were assigned to functional groups based on vegetative attributes: (a) Raunkiaer life-form and (b) height of adult plants, and regenerative attributes: (c) mode of dispersal and (d) pollination class. The distribution of attributes was related to neighbourhood parameters that reflect the composition, distribution and diversity of nine habitat classes within a 25-m radius from the focal plot. Regression trees were used to analyse counts of attributes per plot. Best predictors were neighbourhood scores for open areas, road-side habitat, and neighbourhood diversity. The correlation between individual functional attributes and neighbourhood parameters were presented in a correlation matrix. A cluster analysis, representing a first step towards the construction of plant functional types, resulted in five groups characterised by a particular combination of functional attributes and preference of neighbourhood.     

Cycles in voles and small game in relation to variations in plant production indices in Northern Sweden

Population dynamics for voles (Cricetidae), Tengmalm's owl (Aegolius funereus (L.)), red fox (Vulpes vulpes (L.)) willow grouse (Lagopus lagopus (L.)), black grouse (Lyrurus tetrix (L.)), capercaillie (Tetrao urogallus L.), hazel hen (Tetrastes bonasia (L.)), mountain hare (Lepus timidus L.) and tularemia (Francisella tularensis (McCoy & Chapin)) and game bird recruitment were studied by index methods in northern Sweden. In addition contemporary temperature records and spruce (Picea abies (L.) Karst.) and pine (Pinus silvestris L.) cone crops (as indices for plant production) and the occurrence of forest damage, caused by voles eating bark, were studied.During 1970–80 two synchronous 4-year cycles were observed for voles, predators (Tengmalm's owl and red fox) and their alternative prey species (grouse and mountain hare). In grouse the change of numbers was correlated with that of recruitment. Autumn vole numbers peaked about a year before the other species and extensive forest damage occurred at winter peak densities of voles. These population fluctuations are consistent with a predator-prey model for their regulation. In short the model suggests that vole-food plant interactions trigger the cycle of voles, that voles generate the cycle of predators and that these in turn synchronize alternative prey populations to the others at vole declines.For voles, grouse and red fox the amplitude was higher in the first cycle compared to the second one whilst the opposite was true for the mountain hare. Although temperature and cone crops showed large interannual variations they still implied that herbivore food conditions were better during the former cycle. Hence, the reduction of the amplitude of the vole cycle may be explained by inter-cyclic differences in plant food conditions, implying food shortage (as indicated by bark-eating) at different population levels. The similar decrease of grouse and red fox populations may also be explained by deteriorated food conditions and/or for the fox by an outbreak of sarcoptic mange (Sarcoptes scabiae var. vulpes). The increased amplitude of the mountain hare cycle was part of a long-term rise in numbers after a tularemia epidemic in 1967. This is interpreted as a recovery, probably towards the generally higher pre-epidemic population level.