Effect of Light Quality (Red:Far-red Ratio) at the Apical Bud of the Main Stolon on Morphogenesis of Trifolium repens L.

A controlled environment experiment investigated whether thered:far-red (R:FR) ratio of light at the apical bud of the mainstolon could alter plant morphogenesis in clonal cuttings ofwhite clover (Trifolium repens L.) The apical bud included theapical meristem, five to six developing leaf primordia withassociated axillary bud primordia and stipules and the firstemerged folded leaf until development was greater than 0·3on the Carlson scale. Three light regimes were imposed on theapical bud by collimating light from R or FR light-emittingdiodes so that the R:FR ratio of light incident at the apicalbud was set at 0·25, 1·6 or 2·1, withoutsignificantly altering photosynthetically active radiation.The effect of these light regimes on white clover seedling growthwas also tested. At a low R:FR ratio seedling hypocotyl and cotyledon lengthswere significantly longer. However, with the cuttings, the lighttreatments did not alter node appearance rate or internode lengthof the main stolon, petiole length, area of leaves or totalshoot dry matter. There was one significant photomorphogeneticresponse in the cuttings, a delay of 0·5 of a phyllochronin the appearance of branches from axillary buds in the lowR:FR ratio treatment relative to the other treatments. Wherebranch appearance was delayed plants had fewer branches. Thisdifference could be ascribed solely to a delay in branch appearanceas there were no significant treatment effects on either theinitiation of axillary bud primordia within the apical bud,the probability of branching or on the rate of growth of branchesafter appearance. Because treatment of the apical bud inducedonly one of the many previously observed responses of whiteclover to a decrease in the R:FR ratio of light, we concludethat other plant organs must also sense the quality of incidentlight.Copyright 1994, 1999 Academic Press White clover, Trifolium repens, apical bud, light quality, red:far-red ratio, light-emitting diode, branching, axillary buds, photomorphogenesis     

Cutting edge: precursor frequency affects the helper dependence of cytotoxic T cells.

Generation of CTL immunity often depends on the availability of CD4 T cell help. In this report, we show that CTL responses induced by cross-priming can be converted from CD4-dependent to CD4-independent by increasing the frequency of CTL precursors. In the absence of CD4 T cells, high numbers of CTL precursors were able to expand in number and become effector CTL. The ability of high frequencies of CD8 T cells to override help was not due to their ability to signal CD40 via expression of CD154. These findings suggest that when precursor frequencies are high, priming of CD8 T cell responses may not require CD4 T cell help.     

Three-dimensional structure of abnormal human haemoglobins Chesapeake and J Capetown

The replacement of the invariant residue, arginine FG4(92)α, by a leucine in the mutant human haemoglobin Chesapeake causes drastically abnormal functional properties. When the arginine is replaced by a glutamine in haemoglobin J Capetown the mutant protein is almost normal. Crystallographic studies at 5.5 Å resolution show that the deoxy form of these two mutants have no significant structural distortions. In contrast, the structure of oxyhaemoglobin Chesapeake is considerably distorted. It appears that in the oxy form, the leucine side chain introduces impermissibly close van der Waal's contacts which disrupt the structure. This disturbance of the oxy structure is probably responsible for the abnormal properties displayed by haemoglobin Chesapeake. The structural basis for the milder abnormalities of haemoglobin J Capetown is as yet unknown.     

Hyposmolar stimulation of secretion of thyrotropin, prolactin, and luteinizing hormone does not require extracellular calcium and is not inhibited by colchicine, cytochalasin B, ouabain, or tetrodotoxin

Hyposmolar stimulation of thyroid-stimulating hormone, prolactin, and luteinizing hormone secretion by dispersed perifused rat pituitary cells was not depressed by removal of Ca2+ from the perifusion medium or by 0.1 mM colchicine, 20 microM cytochalasin B, 0.1 mM ouabain, or 3 microM tetrodotoxin. The secretory response induced by medium hyposmolarity or by thyrotropin-releasing hormone was not appreciably different at 23, 37, or 43 degrees C, but was markedly reduced or abolished when the experiments were performed at 1 degree C. These data indicate that microtubules or microfilaments, transport of extracellular Ca2+ into the cytoplasm, and plasmalemma ion transport mechanisms sensitive to ouabain or tetrodotoxin are not essential components of the mechanism by which extracellular hyposmolarity induces secretion.     

Ultrastructure of the Flame Bulbs of Urastoma cyprinae (Platyhelminthes, ‘Prolecithophora’, Urastomidae)

The ultrastructure of the flame bulbs of the turbellarian Urastoma cyprinae from Mytilus galloprovincialis in the Mediterranean is described. The nucleus of the terminal cell is located some distance basal to the rootlets of the cilia forming the flame; the cytoplasm contains numerous tubules approximately 54–66 nm in diameter, and vesicles. Thick walled, densely packed rod-like structures coil around each other with a tendency towards longitudinal orientation close to the flame. The rod-like structures tightly surround the basal part of the flame and the distal cytoplasmic tube in the apical part of the flame. Some of them, including the inner predominantly longitudinally directed ones, are continuous with the cytoplasm of the terminal cell, others are continuous with the cytoplasm of the distal cytoplasmic tube. Internal leptotriches arise from the cytoplasm of the terminal cell and intrude between the basal parts of the cilia of the flame. The distal cytoplasmic tube possesses a septate junction. The flame bulb of Urastoma differs distinctly from those known from other Platyhelminthes; implications for the phylogeny of Platyhelminthes are discussed.     

Sustained swimming speeds and myotomal muscle function in the trout, Salmo gairdneri

Rainbow trout were trained for 3–4 weeks in a flume at swimming speeds of 1, 2 and 3 l s⁻¹. For each experiment growth rates were estimated and by measuring the hypertrophy of red and mosaic skeletal muscle fibres their function was described at particular swimming speeds and compared with earlier experiments on coalfish using the same technique.
Maximum growth, compared with controls in still water, occurred at swimming speeds of 1 l s⁻¹. At this speed the trout mosaic muscle fibres hypertrophied by 40% but the red muscle fibres showed only a 25% hypertrophy. It is suggested that natural swimming speeds are close to 1Ls^−l and the trout mosaic fibres are better adapted for use at this speed in comparison with coalfish white muscle fibres.     

Habituation of western gorillas: the process and factors that influence it

Habituation of western gorillas to human presence is generally an expensive, lengthy and difficult process. Here we describe the habituation process for two groups of western gorillas at the Mondika Research Center, with the hope that the lessons we learned will facilitate future gorilla studies. We expand upon earlier studies by describing the process through complete habituation for both males and females, and for more than one group. The major obstacle to habituation was developing sufficient tracking skills to follow gorilla trail on a daily basis. Once this was achieved, the silverback became semi-habituated (i.e. ignoring human presence during half of contacts) within a year, although the majority of group females continued to avoid humans. As female presence at contacts increased, a period of male recidivism followed, requiring an additional year before his complete habituation was reached. Habituating the females took longer than the male, but we found, contrary to earlier studies, that it consisted of the same stages, including avoidance, aggression, and curiosity before habituation. We compare results between groups and across sites and discuss how factors such as tracking abilities, group size and cohesion, population density and home range overlap, and the manner of approaching gorillas during contacts influence the habituation process.     

Enzymatic basis for the selective inhibition of varicella-zoster virus by 5-halogenated analogues of deoxycytidine.

5-Bromodeoxycytidine (BrdC) and 5-iododeoxycytidine, at a concentration of 100 mug/ml, effectively inhibit the replication of varicella-zoster (VZ) virus in tissue culture. No toxicity could be demonstrated in uninfected cells under the same conditions. Studies on the enzymatic basis for this selective inhibition were undertaken. Infection of human embryonic lung cell monolayers with VZ virus-infected cells results in the induction of thymidine (dT), deoxycytidine (dC), and BrdC kinase activities (which are increased 10-, 40-, and 60-fold, respectively) and in a 70-fold stimulation in the incorporation of 3H nucleotide (5-bromodeoxyuridylate) derived from BrdC into DNA. The thermal stability of the VZ virus-induced activities differs significantly from the activities induced by herpes simplex virus type 1 and herpes simplex virus type 2 and those present in uninfected human embryonic lung cells. The VZ virus-induced dT, dC, and BrdC kinase are similarly affected by temperature and cofractionate upon Sephadex gel filtration, findings consistent with the hypothesis that these activities are the function of a single enzyme: a pyrimidine deoxyribonucleoside kinase. The molecular weight, calculated on the basis of the elution pattern on Sephadex G-150, is 70,000. Kinetic studies, demonstrating that dT and dC competively inhibit the phosphorylation of BrdC, are consistent with the phosphorylation of these substrates at a common active site. Kinetic parameters include: KidT = 0.6 MUM; KidC = 60 muM; KmBrdC = 8.5 muM. In contrast to its relatively high affinity for the VZ virus-induced kinase, BrdC is a relatively poor substrate for the host kinases. Therefore, the basis for the selective inhibition of VZ virus by 5-halogenated analogues of dC is reflected in the induction of a pyrimidine deoxyribonucleoside kinase with a high affinity for BrdC.