The raz1 mutant of Arabidopsis thaliana lacks the activity of a high-affinity amino acid transporter

The raz1 mutant of Arabidopsis thaliana (L.) Heynh. has been selected as resistant to the toxic proline analogue, azetidine-2-carboxylic acid (2AZ). Seedlings of the mutant tolerated fivefold higher concentrations of 2AZ (ED₅₀ = 0.25 mM) than the wild-type seedlings (ED⁵⁰ = 0.05 mM). The mutant gene was found to be semi-dominant and the corresponding RAZ1 locus was mapped on chromosome 5 at 69.6±1.8 cM. The resistance to 2AZ could be fully and exclusively accounted for by the lower uptake rate of the proline analogue in the mutant. The influx of L-proline in roots of wild-type seedlings could be dissected into two components: (i) a component with a high affinity and a low capacity for l-proline (K _m≈20 gmM, V _max≈60 nmol·(g FW)^-1·h^-1) and also a high affinity for L-2AZ (K _i≈40 μM) and (ii) a low-affinity, high-capacity component (K _m≈5 mM: V _max = 1300 nmol·(g FW)^-1·h^-1). Clearly, the raz1 mutation affects the activity of a high-affinity transporter, because the high-affinity uptake of proline in the mutant was at least fivefold lower than in the wild-type, whereas the low-affinity uptake was unchanged.     

Characterization of a highly structured domain in Tbp2 from Neisseria meningitidis involved in binding to human transferrin.

The binding of iron-loaded human transferrin at the surface of Neisseria meningitidis is mediated by two polypeptides, Tbp1 and Tbp2. Predicted Tbp amino acid sequences from N. meningitidis strains are highly divergent. This variability is particularly pronounced throughout the Tbp2 polypeptide. In this study, a highly structured and extremely stable Tbp2 domain of about 270 to 290 amino acids which is involved in the binding to transferrin and whose position is well conserved has been characterized. The conservation of such a remarkable structure in a very divergent protein domain (there is only 43% amino acid identity within this region) suggests that is plays an essential biological role and raises a number of questions regarding tbp2 evolution.     

Thiophene synthesis and distribution in young developing plants of Tagetes patula and Tagetes erecta

Thiophene synthesis and accumulation were investigated in organsof Tagetes patula and T. erecta. Thiophene accumulation startedrapidly in germinating seedlings of both species. Roots andhypocotyls were the major thiophene accumulating organs and5-(3-buten-1-ynyl)-2, 2-bithienyl (BBT) and 5-(4-acetoxy-1-butynyl)-2,2 -bithienyl (BBTOAc) were the major accumulated compounds.Higher thiophene concentrations were reached in Tagetes patulathan in T. erecta. Accumulation patterns for individual thiopheneswere different within organs, between organs and between bothspecies. Within hypocotyls of Tagetes patula, thiophene concentrationswere high in the epidermis and the vascular tissue and low inthe parenchymatic tissues of cortex and pith. Synthesis of thiopheneswas high in the roots and hypocotyls and very low in the leaves.Transport of thiophenes from the roots into the shoot occurred,but the rate of transport was too low to explain the high concentrationsin the hypocotyl. It is concluded that for the main part thiophenesare accumulated where they are synthesized. Key words: Tagetes, hiophenest, synthesis, accumulation, secondary metabolites     

Expression of the Phytophthora infestans ipiB and ipi0 genes in planta and in vitro

The ipiB and ipiO genes of the potato late blight fungus Phytophthora infestans (Mont.) de Bary were isolated from a genomic library in a screen for genes induced in planta. Expression of these genes was studied during pathogenesis on various host tissues and different host plants, some of which show specific resistance against P. infestans infection. During pathogenesis on leaves and tubers of the fully susceptible potato cultivar (cv.) Ajax and on leaves of the fully susceptible tomato cv. Moneymaker, the P. infestans ipiB and ipiO genes show a transient expression pattern with highest mRNA levels in the early stages of infection. During the interaction with leaves of the partially resistant potato cv. Pimpernel, the expression is also transient but accumulation and disappearance of the mRNAs is delayed. Also in P. infestans inoculated onto a race-specific resistant potato cultivar and onto the nonhost Solanum nigrum, ipiB and ipiO mRNA is detectable during the initial stages of infection. Apparently, the expression of the ipiB and the ipiO genes is activated in compatible, incompatible and nonhost interactions. In encysted zoospores, ipiB and ipiO mRNA accumulation was not detectable, but during cyst germination and appressorium formation on an artificial surface the genes are highly expressed. Expression studies in mycelium grown in vitro revealed that during nutrient starvation the expression of the ipiB and ipiO genes is induced. For ipiO gene expression, carbon deprivation appeared to be sufficient. The ipiO gene promoters contain a sequence motif that functions as a glucose repression element in yeast and this motif might be involved in the regulation of ipiO gene expression.     

Visiting bags: a labile thermal environment.

OBJECTIVE--To define usual colour and site of storage of visiting bags in general practitioners'' cars and to investigate effect of these variables on temperature inside bag. DESIGN--Questionnaire to general practitioners; serial temperature measurements from paired black visiting bags at different storage sites and from bags of different colour. SETTING--South Devon coastal town during May and June. SUBJECTS--200 general practitioners, of whom 145 returned legible questionnaires. MAIN OUTCOME MEASURES--Bag colour, duration and site of storage, temperature inside black bags at defined storage sites, and effects of bag colour on internal temperature. RESULTS--111 (77%) of the general practitioners carried a black visiting bag, and 76 kept their bag in their car all day. The bag was coolest in the car boot, but irrespective of storage site, maximum internal temperature of the bag was always over 25 degrees C and reached up to 80 degrees C. Spraying a black bag silver significantly reduced the bag''s internal temperature (mean difference 8.37 degrees C (95% confidence interval 6.68 to 9.86 degrees C) df = 59, t = 10.29, P < 0.001). CONCLUSIONS--General practitioners should use a silver coloured visiting bag; when visiting, they should store it in their car boot; at other times they should remove it to a cooler site.     

A SEARCH FOR SOME ANG1OSPERM HORMONES AND THEIR METABOLITES IN CAULERPA PASPALOIDES (CHLOROPHYTA)1

The best available methods were used to search for an-giosperm hormones in the green alga Caulerpa paspa-loides (Bory) Greville. Solvent partitioning of methanol extracts led to acidic ethyl acetate fractions that it were run through high-performance liquid chromatography. Each of the resulting 25 fractions was divided in half so that one half was tested in the dwarf rice or lettuce hypocotyl assays for gibberellins and the other half was methylated and silylated for capillary gas chromatography combined with computerized mass spectrometry. By comparing algal mass spectra with spectra in the extensive library of mass spectra and associated Kovats Retention Indices that MacMillan's Bristol group has amassed, indole-3-acetic acid's presence in the alga was confirmed and dioxindole-3-acetic acid was found. However, despite the presence of several peaks of gibberellin-like activity in the bioassays, no gibberellin or gibberellin metabolite was found in the thousands of full mass spectra examined. The gibberellin-like activity in the acidic ethyl acetate fractions was therefore presumably not from any gibberellin known from vascular plants.     

Rhizome gravitropism precedes gravimorphogenesis after inversion of the green algal coenocyte Caulerpa prolifera (Caulerpales)

Previous investigations reported that the marine alga Caulerpa prolifera, a giant coenocyte, had a fast morphogenetic response to a change in position with regard to gravity: the next rhizoid formed approximately 1 day later on the new underside of the inverted rhizome (Jacobs and Olson, 1980, American Journal of Botany 67: 141–146). Preceding the change in site of rhizoid development was a striking accumulation of amyloplasts at the new prospective rhizoid-initiation site in the rhizome tip. Detailed monitoring with video equipment of inverted Caulerpa plants, growing under controlled conditions, now reveals that after the amyloplast accumulation, but before the gravimorphogenetic effect on rhizoid development, the inverted rhizome tip shows a negative gravitropism that restores it to its normally upturned position. Because the experiments were performed with two-sided illumination, this was clearly not a phototropic response.     

Phospholipase A2 inhibitors from marine algae

Twelve out of twenty-nine compounds isolated from benthic marine algae from the phyla Chlorophyta, Phaeophyta and Rhodophyta have been found to be potent inhibitors of bee venom derived phospholipase A₂ (PLA₂) (> 50%) in the M range. The compounds investigated were from: Bryopsis pennata, Rhipocephalus phoenix, Caulerpa prolifera, C. racemosa, C. bikinensis, Cymopolia barbata, Laurencia cf. palisada, Laurencia sp., Ochtodes crockeri, Liagora farinosa, Sphaerococcus coronipifolius, Phacelocarpus labillardieri, Dictyota sp., B furcaria galapagensis, Stypopodium zonale, Dictyopteris undulata, Stoechospermum marginatum, Dictyopteris divaricata, Dilophus fasciola and Dilophus sp. This is the first report of bee venom PLA₂ inhibition in vitro by pure compounds isolated from marine algae.