Kaurene Synthetase Activity in Helianthus annuus L. : Increases in Enzyme Activity after Storage of Seedlings in Liquid Nitrogen

In previous studies, the conversion of geranylgeranyl pyrophosphate to ent-kaurene (kaurene synthetase AB activity) could not be detected readily in crude extracts of sunflower (Helianthus annuus L.) seedlings (Shen-Miller, West 1982 Plant Physiol 69: 637-641). These investigations also revealed the presence of inhibitors for Marah macrocarpus kaurene synthetase AB activity in crude extracts of sunflower seedlings. It has now been found that crude extracts prepared from intact sunflower seedlings stored in liquid N₂ for several days have greatly enhanced AB activity in comparison with frozen, but not stored, controls. The levels of activity for the conversion of copalyl pyrophosphate to ent-kaurene (kaurene synthetase B activity) are affected only slightly by storage of intact seedlings in liquid N₂. Extracts from intact seedlings that had been stored in liquid N₂ also showed less inhibitory activity for Marah macrocarpus endosperm kaurene synthetase AB activity.     

Comparative reproductive patterns in culture of differentGigartina subgenusMastocarpus andPetrocelis populations from northern Japan

Samples of theGigartina pacifica-ochotensis complex were collected at 21 localities around Hokkaido and northern Honshu. The carpospore and blade tip cultures showed 3 reproductive patterns. (1) 237 (86.8%) of the 273 cultured isolates derived from single plants have a direct type of life history. (2) 29 (10.6%) isolates exhibited a heteromorphic type with the alternation of foliose gametophytes and crustose tetrasporophytes. (3) 7 (2.6%) isolates showed a mixed pattern in which carposporelings developed intoPetrocelis-like crusts, basal discs with uprightGigartina blades, or chimera-like discs with compositePetrocelis-Gigartina anatomy. CulturedGigartina blades derived from bothG. pacifica andG. ochotensis were similar in morphology. In 18 cultures from 5 localitiesPetrocelis tetraspores developed into dioeciousGigartina gametophytes. A single tetrasporeling grew into aGigartina plant that reproduced directly. In hybridization experiments with 8 male and 14 female isolates from 4 localities on Hokkaido 85 (78.0%) of 109 were positive. On the basis of these and earlier studies it is concluded that a single species is present in northern Japan:G. pacifica Kjellm. has priority overG. ochotensis (Rupr.) Rupr. ex Yendo.     

Fc receptors on mouse effector cells mediating natural cytotoxicity against tumor cells.

Mouse effector cells mediating natural cytotoxicity against tumor cells have been previously thought to be lymphocytes that lack any detectable cell surface markers. The present study presents evidence for receptors for the Fc portion of IgG on these cells. By adsorption of cytotoxic spleen cells on monolayers of sheep erythrocytes (E) plus IgG antibodies to sheep erythrocytes (EA), 50 to 96% of the total cytotoxic reactivity could be removed. Parallel adsorption of cells on E monolayers or on EA monolayers coated with protein A, to block the Fc portion of IgG, resulted in little or no depletion of cytotoxic activity. The presence of Fc receptors on the NK cells was confirmed by combining EA rosette formation with velocity sedimentation at unit gravity. Peak cytotoxicity occurred at the same sedimentation velocity as the peak of Fc-positive cells. After EA rosette formation, there was a shift to a higher sedimentation velocity in the Fc-positive cells and in the natural cytotoxic activity. The increase in sedimentation velocity of NK activity that was observed in these experiments indicated that most of the cells had only bound a small number (three or four) of antibody-coated erythrocytes. Together, these data indicate that cells with Fc receptors account for most of the total lytic activity of normal mouse spleen cells.     

CULTURE AND HYBRIDIZATION STUDIES ON GIGARTINA PAPILLATA (RHODOPHYTA)1

The foliose red alga Gigartina papillata (C. Ag.) J. Ag. was studied in culture to determine its life history and possible relationship to the life history of Petrocelis middendorffii (Ruprecht) Kjellman. Carpospores cultured from individual female plants gave rise to either crustose Petrocelis-like plants that reproduced by tetraspores, or to another generation of foliose female (cystocarpic) plants that reproduced by carpospores. Apices cultured from blades of individual field-collected female plants produced either papillae with many procarps that developed cystocarps only when crossed with male plants, or papillae with few procarps that produced cystocarps in the absence of male plants. The results are interpreted to demonstrate that two types of life history occur in G. papillata: one, a sexual life history involving a crustose tetrasporophyte; the other, a possibly apomictic life history involving only cystocarpic plants. Hybridization experiments demonstrated, that G. papillata is interfertile with Gigartina-phase gametophytes cultured from tetraspores of P. middendorffii. Sexual plants of G. papillata are postulated to represent the naturally-occurring gametophyte of P. middendorffii in California. The possible relationships of the sexual and apomictic plants of G. papillata are discussed.     

Role of SSB protein in RecA promoted branch migration reactions

Summary The RecA protein ofEscherichia coli is essential for genetic recombination and postreplicational repair of DNA. In vitro, RecA protein promotes strand transfer reactions between full length linear duplex and single stranded circular DNA of X174 to form heteroduplex replicative form II-like structures (Cox and Lehman 1981a). In a similar way, it transfers one strand of a short duplex restriction fragment to a single stranded circle. Both reactions require RecA and single strand binding protein (SSB) in amounts sufficient to saturate the ssDNA. The rate and extent of strand transfer is enhanced considerably when SSB is added after preincubation of the DNA with RecA protein. In contrast, SSB protein is not required for RecA protein catalysed reciprocal strand exchanges between regions of duplex DNA. These results indicate that while SSB is necessary for efficient transfer between linear duplex and ssDNA to form a single heteroduplex, it is not required for branch migration reactions between duplex molecules that form two heteroduplexes.Abbreviations SSB single strand binding protein - ssDNA single stranded DNA - X phage X174 - bp base pairs - ATP[S] adenosine 5-O-(gamma-thiotriphosphate)     

Muscarinic cholinergic and preganglionic physiological stimulation increase cyclic GMP levels in guinea-pig superior cervical ganglia.

Abstract— Incubation of guinea-pig superior cervical ganglia in 500μ4mUm -carbachol for 2min increased cyclic GMP levels 530% over control values. The increase was blocked by prior incubation in 300μm atropine. No increase in cyclic GMP levels after incubation in 100 μm -l -norepinephrine was observed. Preganglionic physiological stimulation for 8 min at 10 Hz increased cyclic GMP levels 180% over control values. We conclude that both muscarinic cholinergic and preganglionic physiological stimulation increase cyclic GMP levels in guinea pig superior cervical ganglia, while norepinephrine has no effect.     

Effect of incubation temperature on the frequency of sister chromatid exchanges in Bloom's syndrome lymphocytes

Summary The effect of incubation temperature on the frequency of sister chromatid exchange (SCE) has been studied in blood cultures from three Bloom's syndrome (BS) patients, three controls, and three BS heterozygotes. All cell types show slight increases of SCE at 39°C while at 35°C and 32°C, SCE is reduced considerably in BS and slightly increased in normal cells. Prolonging lymphocyte culture to 140 h and adding BUdR for the last two S periods causes a similar decrease in the percentage of SCE in normal and BS cells but, while the latter show a further reduction if they are incubated at 32°C during BUdR labelling, the normal cells show an increase. Therefore, BS and control lymphocytes respond similarly to changes in incubation time and differently to changes in incubation temperature. The possibility that the discrepant behaviour of the BS and control cultures may be due to different growth kinetics of their B and T lymphocytes has been discussed but considered unlikely. Since low temperature lengthens the cell cycle, it has been suggested that our findings and those published by others on co-cultivation experiments (except those of Tice et al. 1978) can be explained by assuming that slow growth reduces SCE in BS cells. This, and unpublished observations (Giannelli et al. 1981), suggest that some imbalance in the factors responsible for DNA replication may exist in BS and possibly account for the high level of SCE.