Morphological plasticity of white clover (Trifolium repens L.) in response to spatial and temporal resource heterogeneity

Heterogeneity in resource distribution has been an important selective force shaping morphological plasticity in plants. When resources are patchily distributed, changes in morphology are assumed to affect placement of the resource-acquiring structures (roots and leaves) such that they enhance the plant's capacity for resource uptake. Morphological development of four white clover (Trifolium repens) genets was studied in two glasshouse experiments. In the spatial experiment, two substrates (potting soil and sand) were used to create the following discrete patch combinations, sand-sand, soil-sand, sand-soil, and soil-soil. Stolons grew across each combination and consecutive ramets from a given stolon permitted rooting in each substrate pair. In the temporal experiment, the two ramets were first rooted in sand only. After a predetermined period, the sand was replaced and the same substrate combinations created as in the spatial experiment. In each experiment, total developmental time within a given substrate combination was held constant. All measurements were conducted on the second (i.e., younger) of the ramet pairs. In the spatial experiment, ramets rooted in soil had significantly greater branching frequencies than ramets rooted in the sand substrate, regardless of genotype or the preceding substrate type. Ramets occupying the sand-sand combination had the lowest branching frequencies but branch production for the ramet rooted in sand was higher if the preceding ramet was rooted in soil. The substrate occupied by a preceding ramet had no influence upon branching propensity if a ramet was rooted in soil. There were no significant differences in branching frequencies between the sand and soil substrates in the temporal experiment. The relationship between branching and substrate thus depended upon whether a ramet was exposed to a given substrate type during its early development. In both experiments, branched ramets in the soil-soil combinations had significantly greater shoot mass than corresponding ramets in the sand-sand combinations. Internode length was significantly shorter in the soil versus sand combinations of the spatial experiment but was unaffected by substrate in the temporal experiment. Leaf area and stolon width showed significant genotype2treatment interactions in both experiments but no consistent trends were evident; petiole length was unaffected by substrate.     

Influence of permanent raised bed planting and residue management on physical and chemical soil quality in rain fed maize/wheat systems

Densely populated, intensively cropped highland areas in the tropics and subtropics are prone to erosion and declining soil fertility, making agriculture unsustainable. Conservation agriculture in its version of permanent raised bed planting with crop residue retention has been proposed as an alternative wheat production system for this agro-ecological zone. A five years field experiment comparing permanent and tilled raised beds with different residue management under rainfed conditions was started at El Batán (Mexico) (2,240 m asl; 19.31°N, 98.50°W; Cumulic Phaeozem) in 1999. The objective of this study was to determine the soil quality status after five years of different management practices. The K concentration was 1.65 times and 1.43 times larger in the 0–5 cm and 5–20 cm profiles, respectively, for permanent raised beds compared to conventionally tilled raised beds. The Na concentration showed the opposite trend. Sodicity was highest for conventionally tilled raised beds and for permanent raised beds it increased with decreasing amounts of residue retained on the surface. Permanent raised beds with full residue retention increased soil organic matter content 1.4 times in the 0–5 cm layer compared to conventionally tilled raised beds with straw incorporated and it increased significantly with increasing amounts of residue retained on the soil surface for permanent raised beds. Soil from permanent raised beds with full residue retention had significantly higher mean weight diameter for wet and dry sieving compared to conventionally tilled raised beds. Permanent raised beds with full residue retention had significantly higher aggregate stability compared to those with residue removal. A lower aggregation resulted in a reduction of infiltration. Principal component analysis (PCA) was performed using these soil physicochemical variables that were significantly influenced by tillage or residue management. The PC1 and PC2 separated the conventionally tilled raised beds from the permanent raised beds and PC3 separated permanent raised beds with at least partial residue retention from permanent raised beds with no residue retention. These clear separations suggest that tillage and residue management have an effect on soil processes. The research indicates that permanent raised bed planting increases the soil quality and can be a sustainable production alternative for the (sub)tropical highlands. Extensive tillage with its associated high costs can be reduced by the use of permanent raised beds while at least partial surface residue retention is needed to insure production sustainability.     

Growth and Heavy Metal Binding Properties of Transgenic Chlamydomonas Expressing a Foreign Metallothionein Gene

We have compared the growth rates and cadmium binding capacity of wild-type and transgenic Chlamydomonas reinhardtii cells expressing a foreign class-II metallothionein. We observed that cells expressing metallothionein grew to significantly higher cell densities than wild-type cells in the presence of a toxic cadmium concentration (40 μM). When grown at a low (5 μM) cadmium concentration, cells expressing metallothionein bound twofold more cadmium (0.43 μg Cd)mg Ch1) than wild-type. At cadmium concentrations (40 μM), which induce phytochelatin synthesis in wild-type cells the cadmium binding capacity of both wild-type (79.6 μg Cd)mg Ch1) and transformed cells (86.4 μg Cd)mg Ch1) was similar; however, the transformed cells grew to higher densities than the wild type. These results suggest that under conditions that apparently induce phytochelatin expression, the presence of metallothionein in the cytoplasm reduces heavy metal toxicity. Furthermore, because cells expressing metallothionein grow to higher densities than wild-type cells at a toxic cadmium concentration (40 μM), the transgenic cells sequester more total cadmium (9% of total Cd) from the medium than the wild type (5.5% of total Cd). These results indicate that the trace-metal binding properties of Chlamydomonas can be enhanced through the expression of trace-metal-specific binding proteins.     

Contact x-ray microscopy. A new technique for imaging cellular fine structure.

Contact x-ray microscopy potentially allows living, wet cells to be visualized at a resolution of up to 100 A. Furthermore, differential absorption by specific elements permits the study of the distribution of those elements in biological specimens. In contact x-ray microscopy, soft x-rays (10 A to 100 A) pass through a biological sample and expose an underlying x-ray sensitive polymer (resist), producing an image that reflects the photon absorbance within the specimen. The high penetrating power of soft x-ray enables images to be obtained from specimens up to several microns thick. In this paper, the technique is described, some of the areas currently under study are considered, and biological examples of the use of contact x-ray microscopy are given.     

Towards the development of selective amine oxidase inhibitors. Mechanism-based inhibition of six copper containing amine oxidases.

Four substrate analogs, 4-(2-naphthyloxy)-2-butyn-1-amine (1), 1,4-diamino-2-chloro-2-butene (2), 1,6-diamino-2,4-hexadiyne (3), and 2-chloro-5-phthalimidopentylamine (4) have been tested as inhibitors against mammalian, plant, bacterial, and fungal copper-containing amine oxidases: bovine plasma amine oxidase (BPAO), equine plasma amine oxidase (EPAO), pea seedling amine oxidase (PSAO), Arthrobacter globiformis amine oxidase (AGAO), Escherichia coli amine oxidase (ECAO), and Pichia pastoris lysyl oxidase (PPLO). Reactions of 1,4-diamino-2-butyne with selected amine oxidases were also examined. Each substrate analog contains a functional group that chemical precedent suggests could produce mechanism-based inactivation. Striking differences in selectivity and rates of inactivation were observed. For example, between two closely related plasma enzymes, BPAO is more sensitive than EPAO to 1 and 3, while the reverse is true for 2 and 4. In general, inactivation appears to arise in some cases from TPQ cofactor modification and in other cases from alkylation of protein residues in a manner that blocks access of substrate to the active site. Notably, 1 completely inhibits AGAO at stoichiometric concentrations and is not a substrate, but is an excellent substrate of PSAO and inhibition is observed only at very high concentrations. Structural models of 1 in Schiff base linkage to the TPQ cofactor in AGAO and PSAO (for which crystal structures are available) reveal substantial differences in the degree of interaction of bound 1 with side-chain residues, consistent with the widely divergent activities. Collectively, these results suggest that the development of highly selective amine oxidase inhibitors is feasible.     

Tempo and mode of concerted evolution in the L1 repeat family of mice

A 300-bp DNA sequence has been determined for 30 (10 from each of three species of mice) random isolates of a subset of the long interspersed repeat family L1. From these data we conclude that members of the L1 family are evolving in concert at the DNA sequence level in Mus domesticus, Mus caroli, and Mus platythrix. The mechanism responsible for this phenomenon may be either duplicative transposition, gene conversion, or a combination of the two. The amount of intraspecies divergence averages 4.4%, although between species base substitutions accumulate at the rate of approximately 0.85%/Myr to a maximum divergence of 9.1% between M. platythrix and both M. domesticus and M. caroli. Parsimony analysis reveals that the M. platythrix L1 family has evolved into a distinct clade in the 10-12 Myr since M. platythrix last shared a common ancestor with M. domesticus and M. caroli. The parsimony tree also provides a means to derive the average half-life of L1 sequences in the genome. The rates of gain and loss of individual copies of L1 were estimated to be approximately equal, such that approximately one-half of them turn over every 3.3 Myr.