Nutrient inflows into apple roots. I. 32P-orthophosphate uptake from solution by M.9 rootstocks and Worcester Pearmain seedlings

Abstract. The rates of uptake of ³²P-labelled orthophosphate by whole root systems of young apple trees (M.9 rootslocks and Worcester Pearmain seedlings) were measured in solution culture. Using a solution depletion technique, the ³²P-phosphate uptake rates per unit length, surface area or fresh weight of roots were determined as a function of ³²P-phosphate concentration in solution at the root surface over the range 0.25–10 mmol m⁻³. The effect of P concentration within various plant parts on the relation between uptake rate and external P concentration was studied using plants differing in internal P levels.
The apparent minimutn P concentration below which P uptake ceased was of the order of 0.25–0.50 mmol m⁻³. Fluxes, inflows and unit absorption rates increased approximately proportionately with solution concentration up to 10mmolm⁻³. Except perhaps in the case of the low-P M.9 plant, there was no evidence of a diminishing returns type of relationship over the range of solution concentrations examined. The threshold P concentration in solution above which uptake rates cease to increase thus appears to be higher for apples than for other species.
At any given P concentration, fluxes, inflows and unit absorption rates were higher for M.9 than for Worcester and for low-P plants than for high-P plants. The difference between plants of different P status was more marked for M.9 and seems to be more closely related to shoot P levels than to root P.     

The Possible Involvement of Lipoxygenase in Downy Mildew Resistance in Pearl Millet

The downy mildew disease, incited by Sclerospora graminicola,is a major biotic constraint for pearl millet production inthe semi-arid tropics. Sources of resistance to this diseasehave been identified. However, the mechanism of host resistancestill remains obscure. The enzyme lipoxygenase (LOX) is knownto play a role in disease resistance in many host-pathosystems.In the present study, LOX activity was tested in seeds of differentgenotypes of pearl millet with different susceptibility to downymildew. The LOX assay of the seeds indicated a good correlationbetween enzyme activity and their downy mildew reaction in thefield. Maximum activity was recorded in seeds of highly resistantgenotypes and minimum activity was found in the highly susceptiblegenotypes. Seeds obtained from plants recovered from the downymildew disease had more LOX activity than that of the originalparent seeds. Thus, in seeds, the LOX activity can be used asa biochemical marker for screening different genotypes of pearlmillet for downy mildew. The study, carried out in the susceptiblegenotype of pearl millet seedlings, showed that LOX activitydecreased after inoculating with S. graminicola zoospores whencompared with uninoculated controls. However, a significantincrease in the enzyme activity was observed on the second andthird days after inoculation in resistant seedlings. The possiblerole of LOX in conferring resistance to downy mildew infectionof pearl millet is discussed. Key words: Lipoxygenase, pearl millet, downy mildew     

Thermodynamics and Kinetics of MTBE Degradation: A Density Functional Theory Study

Computational studies using density functional theory can help define which of a variety of reactions may be involved in the degradation of the fuel oxygenate methyl tert-butyl ether (MTBE). It is shown that hydrolysis of MTBE in the vapor phase or in neutral aqueous media, as well as its unimolecular decomposition, are not significant degradation mechanisms. The acid catalyzed hydrolysis of MTBE is a more feasible degradation pathway and is shown to proceed via tert-butyl carbonium ion formation. Hydrogen abstraction is shown to be the dominant first step in the degradation of MTBE initiated by hydroxyl radicals.     

Clinal variation in body size and sexual dimorphism in an Indian fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae)

Geographic variation in body size and sexual dimorphism of the short‐nosed fruit bat (Cynopterus sphinx) was investigated in peninsular India. Bats were sampled at 12 localities along a 1200 km latitudinal transect that paralleled the eastern flanks of the Western Ghats. The geographic pattern of variation in external morphology of C. sphinx conforms to the predictions of Bergmann's Rule, as indicated by a steep, monotonic cline of increasing body size from south to north. This study represents one of the first conclusively documented examples of Bergmann's Rule in a tropical mammal and confirms that latitudinal clines in body size are not exclusively restricted to temperate zone homeotherms. Body size was indexed by a multivariate axis derived from principal components analysis of linear measurements that summarize body and wing dimensions. Additionally, length of forearm was used as a univariate index of structural size to examine geographic variation in a more inclusive sample of bats across the latitudinal transect. Multivariate and univariate size metrics were strongly and positively correlated with body mass, and exhibited highly concordant patterns of clinal variation. Stepwise multiple regression on climatological variables revealed that increasing size of male and female C. sphinx was associated with decreasing minimum temperature, increasing relative humidity, and increasing seasonality. Although patterns of geographic size variation were highly concordant between the sexes, C. sphinx also exhibited a latitudinal cline in the magnitude and direction of sexual size dimorphism. The size differential reversed direction across the latitudinal gradient, as males averaged larger in the north, and females averaged larger in the south. The degree of female‐biased size dimorphism across the transect was negatively correlated with body size of both sexes. Canonical discriminant analysis revealed that male‐ and female‐biased size dimorphism were based on contrasting sets of external characters. Available data on geographic variation in the degree of polygyny in C. sphinx suggests that sexual selection on male size may play a role in determining the geographic pattern of sexual size dimorphism.     

Population genomics of wild and laboratory zebrafish (Danio rerio)

Understanding a wider range of genotype–phenotype associations can be achieved through ecological and evolutionary studies of traditional laboratory models. Here, we conducted the first large‐scale geographic analysis of genetic variation within and among wild zebrafish (Danio rerio) populations occurring in Nepal, India, and Bangladesh, and we genetically compared wild populations to several commonly used lab strains. We examined genetic variation at 1832 polymorphic EST‐based single nucleotide polymorphisms (SNPs) and the cytb mitochondrial gene in 13 wild populations and three lab strains. Natural populations were subdivided into three major mitochondrial DNA clades with an average among‐clade sequence divergence of 5.8%. SNPs revealed five major evolutionarily and genetically distinct groups with an overall F_ST of 0.170 (95% CI 0.105–0.254). These genetic groups corresponded to discrete geographic regions and appear to reflect isolation in refugia during past climate cycles. We detected 71 significantly divergent outlier loci (3.4%) and nine loci (0.5%) with significantly low F_ST values. Valleys of reduced heterozygosity, consistent with selective sweeps, surrounded six of the 71 outliers (8.5%). The lab strains formed two additional groups that were genetically distinct from all wild populations. An additional subset of outlier loci was consistent with domestication selection within lab strains. Substantial genetic variation that exists in zebrafish as a whole is missing from lab strains that we analysed. A combination of laboratory and field studies that incorporates genetic variation from divergent wild populations along with the wealth of molecular information available for this model organism provides an opportunity to advance our understanding of genetic influences on phenotypic variation for a vertebrate species.     

Anatomical diversity of Indian rattan palms (Calamoideae) in relation to biogeography and systematics

Of the 13 genera and 600 species of the subdivision Calamoideae, only four genera– Calamus, Daemonorops, Korthalsia , and Plectocomia –represent the Indian rattans which are found in three major regions: Western Ghats of Peninsular India, Andaman and Nicobar islands and north and north-eastern India. Detailed anatomical survey of 42 species shows considerable differences among the four genera. The vascular bundle in Calamus, Daemonorops and Korthalsia is characterized by a solitary metaxylem vessel and two phloem fields, while Plectocomia shows 1–2 metaxylem vessels and a single phloem field. The mechanical tissues show diversity in Korthalsia and Plectocomia with sclereids as a yellow cap on the outer side of the fibrous sheaths of vascular bundles. The size of the different cells, the diameter of the metaxylem vessel in particular, appears to be related to species habit, geography and stem size. The Andaman and Nicobar islands with equable temperature and high humidity provide the best environment for cane growth–the widest vessels are in canes from this region. While altitudinal influence on vessel diameter appears to be relatively small, the higher latitude is associated with narrow and short vessel elements. With the exception of C. erectus , an erect species with the thickest stem, vessel diameter shows positive correlation with stem diameter. Vessel perforations are simple or rarely scalariform. Climbing palms which grow to enormous heights generally have wider vessels with simple perforations, an adaptation for conductive efficiency. Based on these results, the implications of stem anatomy for rattan biogeography, systematics and identification are discussed, and identification keys to species presented.     

Identification and characterization of expressed sequence tags‐derived simple sequence repeats markers from robusta coffee variety ‘CxR’ (an interspecific hybrid of Coffea canephora × Coffea congensis)

SSR (simple sequence repeats) markers derived from ESTs (expressed sequence tags), commonly called EST‐SSRs or genic SSRs provide useful genetic markers for crop improvement. These are easy and economical to develop as by‐products of large‐scale EST resources that have become available as part of the functional genomic studies in many plant species. Here, we describe for the first time, nine genic‐SSRs of coffee that are developed from the microsatellite containing ESTs from a cDNA library of moisture‐stressed leaves of coffee variety, ‘CxR’ (a commercial interspecific hybrid between Coffea congensis and Coffea canephora). The markers show considerable allelic diversity with PIC values up to 0.70 and 0.75 for Coffea arabica and Coffea canephora, respectively, and robust cross‐species amplification in 16 other related taxa of coffee. The validation studies thus demonstrate the potential utility of the EST‐SSRs for genetic analysis of coffee germplasm.