Relative growth rate correlates negatively with pathogen resistance in radish: the role of plant chemistry

Plant growth rate has frequently been associated with herbivore defence: a large investment in quantitative defence compounds occurs at the expense of growth. We tested whether such a relationship also holds for growth rate and pathogen resistance. For 15 radish (Raphanus sativus L.) cultivars, we determined the potential growth rate and the resistance to fungal wilt disease caused by Fusarium oxysporum. We subsequently aimed to explain a putative negative relationship between growth rate and resistance based on plant chemical composition. Both growth rate and resistance level varied greatly among cultivars. Moreover, there was a strong negative correlation between growth rate and resistance, i.e. there are costs associated with a high resistance level. Roots of slow-growing, resistant cultivars have a higher biomass density. Using pyrolysis mass spectrometry. we part1y explained variation in both growth rate and resistance in terms of the same change in chemical composition. Leaves of slow-growing, resistant cultivars contained more cell wall material. Surprisingly, roots of slow-growing, highly resistant cultivars contained significantly less cell wall material, and more cytoplasmic elements (proteins). We speculate that this higher protein concentration is related to high construction and turn-over costs and high metabolic activity. The latter in turn is thought to be responsible for a rapid and adequate resistance reaction, in which phenols may be involved.     

Possible explanation of the disparity between the in vitro and in vivo measurements of Rubisco activity: a study in loblolly pine grown in elevated pCO2.

Rubisco activity can be measured using gas exchange (in vivo) or using in vitro methods. Commonly in vitro methods yield activities that are less than those obtained in vivo. Rubisco activity was measured both in vivo and in vitro using a spectrophotometric technique in mature Pinus taeda L. (loblolly pine) trees grown using free-air CO2 enrichment in elevated (56 Pa) and current (36 Pa) pCO2. In addition, for studies where both in vivo and in vitro values of Rubisco activity were reported net CO2 uptake rate (A) was modelled based on the in vivo and in vitro values of Rubisco activity reported in the literature. Both the modelling exercise and the experimental data showed that the in vitro values of Rubisco activity were insufficient to account for the observed values of A. A trichloroacetic acid (TCA) precipitation of the protein from samples taken in parallel with those used for activity analysis was co-electrophoresed with the extract used for determining in vitro Rubisco activity. There was significantly more Rubisco present in the TCA precipitated samples, suggesting that the underestimation of Rubisco activity in vitro was attributable to an insufficient extraction of Rubisco protein prior to activity analysis. Correction of in vitro values to account for the under-represented Rubisco yielded mechanistically valid values for Rubisco activity. However, despite the low absolute values for Rubisco activity determined in vitro, the trends reported with CO2 treatment concurred with, and were of equal magnitude to, those observed in Rubisco activity measured in vivo.     

Identification of a stretch-activated monovalent cation channel from teleost urinary bladder cells.

The urinary bladder of euryhaline teleost is an important osmoregulatory organ which absorbs Na+, Cl-, and water from urine. Using patch clamp technique, single stretch-activated channels, which were permeable to K+ and Na+ (PNa/PK approximately 0.75) and had conductances of 55 and 116 pS, were studied. In excised, inside-out patches which were voltage-clamped in the physiological range of membrane potential, the single-channel open probability (Po) was low (approximately 0.02), and increased to a maximum of 0.9 with applied pipette suction. Single-channel conductance also increased with suction. The channels showed adaptation to applied suction and relaxed to a steady-state activity about 20 seconds after application of suction. The Po increased up to 0.9 with strong membrane depolarization (Vm = 0 to +80 mV); however, there was little dependence of Po on membrane potential in the physiological range. The kinetic data suggest that there is one conducting state and at least two non-conducting states of the channel. The open-time constant increased with suction but remained unchanged with membrane potential (Vm = -70 to +60 mV). The mean closed-time of the channel decreased with suction and membrane depolarization. These results demonstrate the presence of a non-selective monovalent cation channel which may be involved in cell volume regulation in the goby urinary bladder. Additionally, this channel may function as an enhancer of Na+ influx and K+ efflux across the bladder cell as part of transepithelial ion transport if it is located in apical membrane.     

Genetic divergence in South African Wildebeest: comparative cytogenetics and analysis of mitochondrial DNA.

The blue and the black wildebeest, Connochaetes taurinus and C. gnou, are currently classified as congeneric, but previous reports have placed C. taurinus in its own genus, Gorgon. To further clarify the evolutionary relationship between these two species, we examined and compared their mitotic chromosomes and mitochondrial DNA (mtDNA). No species-specific G-banded or C-banded chromosomal markers were found, and we conclude that the karyotypes are invariant at the level of resolution obtained. An evolutionary divergence time of approximately 1 million years was calculated from mtDNA restriction fragment data, indicating a close phylogenetic relationship for the two wildebeest species. The low nucleotide diversity detected within the black wildebeest (0.09%) is thought to reflect the recent population bottleneck to which the species has been subjected. In contrast, the limited heterogeneity (0.02%) within the South African blue wildebeest herds sampled in this study was surprising, and we argue that for many populations, especially those on smaller reserves, this may reflect common descent from a small number of animals through management-controlled translocations.     

Anti-insulin antibody structure and conformation. I. Molecular modeling and mechanics of an insulin antibody.

A knowledge-based three-dimensional model of an anti-insulin antibody, 125, was constructed using the structures of conserved residues found in other known crystallographic immunoglobulins. Molecular modeling and mechanics were done with the 125 amino acid sequences using QUANTA and CHARMm on a Silicon Graphics 4D70GT workstation. A minimal model was made by scaffolding using crystallography coordinates of the antibody HyHEL-5, because it had the highest amino acid sequence homology with 125 (84% light chain, 65% heavy chain). The three hypervariable loop turns that are longer in 125 than in HyHEL-5 (L1, L3, and H3) were modeled separately and incorporated into the HyHEL-5 structure; then other amino acid substitutions were made and torsions optimized. The 125 model maintains all the structural attributes of an antibody and the structures conserved in known antibodies. Although there are many polar amino acids (especially serines) in this site, the overall van der Waals surface shape is determined by positions of aromatic side chains. Based on this model, it is suggested that hydrogen bonding may be key in the interaction between the human insulin A chain loop antigenic epitope and 125.     

Genetic Variation and the Reproduction of Cordylanthus maritimus ssp. maritimus to Sweetwater Marsh, California

This study evaluated the genetic consequences of a reintroduction of the endangered annual plant Cordylanthus maritimus ssp. maritimus to Sweetwater Marsh (San Diego County, California). A survey of 21 enzyme loci in natural populations revealed that genetic diversity is very low and is primarily found as rare alleles at a few loci, making this species especially susceptible to the loss of alleles and heterozygosity through genetic drift. The reintroduction was performed in 1991 and 1992 by sowing seeds (collected from Tijuana Estuary) in numerous small patches of suitable habitat. For this study, leaf tissue was collected from all plants in all patches during flowering in 1995 and surveyed for genotype at the three enzyme loci that are polymorphic at Tijuana Estuary. Rare alleles were absent in 27 out of 30 patches for Pgm-1, in 17 out of 30 patches for Pgm-2, and in 10 out of 11 patches for Mdh-1. In all, half of the patches lacked any rare allele. Rare alleles tended to occur in patches with few individuals. Overall rare allele frequency was lower than in the colonies from which seeds were collected at two of the three loci, and heterozygosity was reduced. The Sweetwater Marsh population is at risk of losing most of its genetic variation at enzyme loci through the extinction of patches with few individuals. Future reintroduction attempts should attempt to create contiguous sets of patches or to periodically reseed existing patches to reduce the loss of genetic variation.