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PubMed1989

Relationships among cold hardiness, root growth potential and bud dormancy in three conifers.

Greenhouse-cultured, container-grown ponderosa pine (Pinus ponderosa var. scopulorum Engelm.), interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) and Engelmann spruce (Picea engelmannii (Parry) Engelm.) were cold acclimated and deacclimated in growth chambers over 19 weeks. Stem cold hardiness, total new root length at 14 days and days to bud break were measured weekly. Relationships among cold hardiness, root growth potential (RGP) and bud dormancy suggest that cold hardiness, which can be measured quickly, could provide a useful basis for estimating the two other parameters. During cold acclimation, there was a lag period in which stem cold hardiness remained at -15 degrees C and RGP was at a minimum, in all three species. Douglas-fir and Engelmann spruce buds remained fully dormant during this lag period. Ponderosa pine buds had no chilling requirement for the loss of dormancy, and reached quiescence during the lag period. Immediately following the lag period, as stem cold hardiness progressed to -22 degrees C, RGP increased to a high plateau in all three species, and Douglas-fir and Engelmann spruce buds approached quiescence. Cold deacclimation and bud development began immediately on exposure to warm, long days, but RGP remained high until stem cold hardiness returned to approximately -15 degrees C. At bud break, cold hardiness and RGP were at the minimum.

Journal Article↗

PubMed1986

Interactions between macrophages and T-lymphocytes: tumor sneaking through intrinsic to helper T cell dynamics.

In a mathematical model of the cellular immune response we investigate immune reactions to tumors that are introduced in various doses. The model represents macrophage T-lymphocyte interactions that generate cytotoxic macrophages and cytotoxic T-lymphocytes. In this model antigens (tumors) can induce infinitely large T-lymphocyte effector populations because effector T-lymphocytes are capable of repeated proliferation and we have omitted immunosuppression. In this (proliferative) model small doses of weakly antigenic tumors grow infinitely large (i.e. sneak through) eliciting an immune response of limited magnitude. Intermediate doses of the same tumor induce larger immune responses and are hence rejected. Large doses of the tumor break through, but their progressive growth is accompanied by a strong immune response involving extensive lymphocyte proliferation. Similarly a more antigenic tumor is rejected in intermediate doses and breaks through in large doses. Initially small doses however lead to tumor dormancy. Thus although the model is devoid of explicit regulatory mechanisms that limit the magnitude of its response (immunosuppression is such a mechanism), the immune response to large increasing tumors may either be a stable reaction of limited magnitude (experimentally known as tolerance or unresponsiveness) or a strong and ever increasing reaction. Unresponsiveness can evolve because in this model net T-lymphocyte proliferation requires the presence of a minimum number of helper T cells (i.e. a proliferation threshold). Unresponsiveness is caused by depletion of helper T cell precursors.

Aging↗

PubMed1978

Cytotoxic effects of maleic hydrazide.

Since 1950, maleic hydrazide (MH) has been introduced into agriculture as a major commercial herbicide and a depressant of plant growth in numerous circumstances such as suppression of sprouting of vegetables and stored food crops, control of sucker growth on tobacco plants, ratardation of flowering and prolongation of dormancy period. Since 1951 MH has been known as an effective chromosome-breaking agent in higher plants, in sharp contrast with its low effect on the chromosomes and general health of tested mammals. The selectivity of action of MH in plants and animals was obviously the main reason of low interest devoted to the chemical by people working the field of environmental mutagenesis. In early works the inhibitory effects of MH on plant growth were mainly considered to result from the suppression of plant metabolism (inhibition of enzymic activity) and interference of the compound with plant hormones and growth regulators. More recently, numerous experiments performed with various plant species have shown that MH acts as an inhibitor of the synthesis of nucleic acids and proteins. Similar results have been obtained with animal tumour cells. The chromosome-breaking effect of MH on plant chromosomes resembles very closely the chromosome-breaking properties of alkylating agents and other mutagenic compounds such as mitomycin C. MH-induced chromosomal aberrations have also been recorded in grasshoppers, fish and mice, although tests with some mammalian cell lines gave negative results. Among higher plants, selective sensitivity to the toxic effects of MH is well proved. This phenomenon seems to be due to the differential ability of various plant species to detoxicate the chemical. Plants can break down MH into several products, one of which, hydrazine, is a well-known mutagen and carcinogen. MH does not seem to be toxic to bacteria and fungi. The compound is degraded by soil microflora and hence can be utilized as a source of nitrogen nutrition. MH proved to be of low toxicity to mammals, but in some instances it decreased the fertility of rats. The reported carcinogenic effects of MH in mice and rats raise the question of its risks to man.

Animals↗

PubMed1999

Gibberellins and Subapical Cell Divisions in Relation to Bud Set and Bud Break in Salix pentandra.

In young plants of Salix pentandra, a temperate zone deciduous woody species, elongation growth ceases and a terminal bud is formed at day lengths shorter than a critical length. This is the first step in dormancy development, making survival under harsh winter conditions possible. Early studies strongly indicate that gibberellin is involved in the photoperiodic control of bud set and bud break. GA(1) action was studied by application under short days to plants where cessation of shoot elongation had occurred, followed by subsequent anatomic investigations of shoot tips. Under short days the frequency of cell division decreased rapidly along with the earlier observed decrease in GA(1) levels. Application of GA(1) to short-day-induced terminal buds rapidly stimulated cell division in apices several days before visible shoot elongation in response to this treatment was observed. One day after GA(1) application a fourfold increase in cell division frequency in apices was observed, increasing to a maximum of sevenfold 2 days after application. Long-day treatment leading to induction of bud break after about 4-6 days was followed by slowly increasing frequency of cell divisions. In earlier studies of this species, short days and gibberellins had no effect on cell elongation. These data show that increased GA(1) content, by application or long-day treatment, results in increased frequency of mitosis. This strongly indicates that GA(1) affects stem elongation in connection with bud set and bud break primarily by affecting cell divisions in subapical tissues.

Journal Article↗

PubMed1997

Effects of near-lethal heat stress on bud break, heat-shock proteins and ubiquitin in dormant poplar (Populus nigra Charkowiensis x P. nigra incrassata).

We assessed the effects of near-lethal heat stress on bud break, heat-shock proteins (HSPs) and ubiquitin in hybrid poplar (Populus nigra (L.) Charkowiensis x P. nigra (L.) incrassata). Shoots, with 10-15 buds each, were collected from September to March and exposed to temperatures between 20 and 60 degrees C for 2 h. Shoots were then placed in a greenhouse at 18-22 degrees C with supplemental light and cumulative bud break was recorded over a 4-week period. Samples of bud tissues were collected during and up to 96 h after heat treatment for protein analysis. De novo synthesis of proteins was monitored by exposing excised buds to [(35)S]-methionine for 3 h before, during, or after heat treatment. Heat treatments of 40-45 degrees C resulted in both a release from endodormancy and a decrease in thermal units needed for bud break during ecodormancy. The response to near-lethal heat stress was complex and was affected by intrinsic thermal sensitivity. Heat treatments were least effective during August and became progressively more effective as endodormancy progressed. In the later stages of ecodormancy, a heat treatment of 45 degrees C either inhibited bud break or killed the buds. Although temperatures of 42.5 to 45 degrees C inhibited incorporation of [(35)S]-methionine into proteins for at least 48 h, several HSPs were synthesized in response to temperatures of 40-45 degrees C. Immunoblots indicated that one of the heat-induced proteins was immunologically related to HSP70. Increases in free and conjugated forms of ubiquitin were also observed in response to heat treatment. Production of HSPs and ubiquitin, however, was not consistently associated with the heat treatments that induced the highest percentage of bud break. The roles of heat-induced protein degradation, HSPs, and ubiquitin in overcoming dormancy by near-lethal heat stress are discussed.

Journal Article↗

PubMed2006

[Responses of Shenyang urban tree phrenology to climate warming].

By using statistic and linear regression methods, this paper studied the last 40 years responses of Shenyang urban tree phenology to climate warming. The results showed that there was a significant correlation between the duration of tree dormancy and the mean air temperature in winter. Appropriate cold condition was beneficial to bud break, and a significant negative correlation was observed between the outset of sprouting and the mean air temperature in winter and early spring. Leaf expansion started 15 days after sprouting, which was mainly affected by the mean air temperature in spring but had no correlation with the temperature in winter. The air temperature within 20-80 days and especially 20-40 days before flowering had a significant effect on the outset of flowering, i. e. , an increasing temperature in spring could advance the outset of flowering. Both sprouting and leaf expansion were negatively correlated with cold index (CI) , but no significant correlation was observed between the outset of flowering and CI. An increase of mean annual air temperature by 1 degree C would advance the outset of sprouting by 9 days, leaf expansion by 10 days, and outset of flowering by 5 days.

China↗

PubMed1999

Preservation of murine embryos in a state of dormancy at 4 degreesC.

With the aim of improving preservation of blood products and organs for transplantation, we designed solutions to induce a state of dormancy in cells and tissues at 4 degreesC. The solutions were devoid of combinations of ions (e.g., K+, Rb+, Cs+, and NH+4 with HCO-3, H2PO-4, and Cl-) that are believed to break down low-density water in the entrance compartments of ion channels, resulting in cyclical open states (normal water) and closed states (low-density water). The total osmolality was always 0.29-0.3 osmol/kgH2O, made up of combinations of a di- or trisaccharide, a compatible solute, sodium sulfate, citrate, or chloride, and 1.75 mM CaCl2. The end point was the ability of murine embryos to progress to hatching in culture after preservation in such a solution at 4 degreesC. Embryos hatched after 5 or 6 days in some preservative solutions compared with 1-3 days in most saline solutions; survival was improved by pretreatment with sodium butyrate.

Animals↗

PubMed2003

Molecular mechanisms of tumor invasion and metastasis: an integrated view.

As tumors progress to increased malignancy, cells within them develop the ability to invade into surrounding normal tissues and through tissue boundaries to form new growths (metastases) at sites distinct from the primary tumor. The molecular mechanisms involved in this process are incompletely understood but those associated with cell-cell and cell-matrix adhesion, with the degradation of extracellular matrix, and with the initiation and maintenance of early growth at the new site are generally accepted to be critical. This article discusses current knowledge of molecular events involved in these various processes. The potential role of adhesion molecules (eg. integrins and cadherins) has undergone a major transition over the last ten years, as it has become apparent that such molecules play a major role in signaling from outside to inside a cell, thereby controlling how a cell is able (or not) to sense and interact with its local environment. Similarly the roles of proteolytic enzymes and their inhibitors (eg. matrix metalloproteinases and TIMPs) have also expanded as it has become apparent that they not only have the abilities to break down the components of the extracellular matrix but also are involved in the release of factors which can affect the growth of the tumor cells positively or negatively. Recent work has highlighted the importance of the later, post-extravasational stages of metastasis, where adhesion and proteolysis are now known to play a role along with other processes such as apoptosis, dormancy, growth factor-receptor interactions and signal transduction. Recent work has also demonstrated that not only the immediate cellular microenvironment, in terms of specific cell-cell and cell-matrix interactions, but also the extended cellular microenvironment, in terms of vascular insufficiency and hypoxia in the primary tumor, can modify cellular gene expression and enhance metastasis. Mechanisms of metastasis appear to involve a complex array of genetic and epigenetic changes many of which appear to be specific both for different types of tumors and for different sites of metastasis. Our improved understanding of the expanded roles of the individual molecules involved has resulted in a mechanistic blurring of the previously described discrete stages of the metastatic process.

Animals↗

PubMed2000

Using (1)H magnetic resonance imaging and complementary analytical techniques to characterize developmental changes in the Zantedeschia Spreng. tuber.

Nuclear magnetic resonance imaging (MRI) and complementary analytical techniques were used to examine tissue structure and developmental changes occurring during active growth in the root tuber of ZANTEDESCHIA: Spreng. cv. Chianti, a commercially significant cut flower. Plants were observed during the period of leaf senescence and tuberization at the end of the first growth cycle of micropropagated plantlets and, following cool storage to break endodormancy, during development occurring after the replanting of ecodormant tubers. MRI distinguished two distinct regions within the tuber, and the differences in the binding state of water in the two regions were reflected in differences in tissue morphology and function. An abundance of free water was observed in tissue comprised of large parenchyma cells, at the base of the tuber. This tissue appeared to be involved in maintaining the viability of the plant during the period of dormancy, a function indicated primarily by increased metabolic activity in this tissue during dormancy, and reduced metabolic activity during periods of active growth. In contrast, water was more tightly bound in tissue comprised of small parenchyma cells. This tissue appeared to operate as a region for dynamic carbohydrate storage. The initial increase in the free water content of this tissue during the growth phase was linked to the mobilization of starch during canopy development. The subsequent decrease in free water in the remainder of the growth period was linked to the reaccumulation of starch while the tuber functioned as a sink for photosynthate prior to canopy senescence.

Carbohydrate Metabolism↗

PubMed2004

Nitrogen storage and its interaction with carbohydrates of young apple trees in response to nitrogen supply.

Bench-grafted 'Fuji/M.26' apple (Malus domestica Borkh.) trees received a constant nitrogen (N) supply (10.7 mM) from bud break to the end of June, and were then fertigated with 0, 5, 10, 15 or 20 mM N in a modified Hoagland's solution for 2 months during the summer. In mid-October, half of the trees fertigated at each N concentration were sprayed twice with 3% urea, whereas the remaining trees served as controls. All trees were harvested after natural leaf fall and were stored at 2 degrees C. Five trees from each of the N treatment combinations were destructively sampled during dormancy to determine the composition of N and total nonstructural carbohydrates (TNC). As the N supply from fertigation increased, amounts of N in both free amino acids and proteins increased, whereas C/N ratios decreased. Foliar urea applications in the fall significantly increased amounts of N in both free amino acids and proteins, but decreased their C/N ratios. Arginine, the most abundant amino acid in both free amino acids and in proteins, accounted for an increasing proportion of N in free amino acids and proteins with increasing N supply from fertigation or foliar urea application. The ratio of protein N to free amino acid N decreased from about 27.1 to 3.2 as N supply from fertigation increased from 0 to 20 mM, and decreased further to 3.0 in response to foliar urea applications in the fall. Concentrations of glucose, fructose, sucrose and TNC decreased as the N supply from fertigation increased, whereas concentrations of sorbitol and starch remained relatively unchanged. Foliar urea applications decreased the concentration of each TNC component and the TNC concentration in each N fertigation treatment. A negative linear relationship was found between carbon in TNC and N in proteins and free amino acids. The sum of carbon in TNC, proteins and free amino acids remained constant in response to N supply from fertigation. However, foliar urea applications decreased the sum of carbon in proteins, free amino acids and TNC because about 21% of the decrease in TNC carbon was not recovered in free amino acids or proteins. Young apple trees store N and carbon dynamically in response to N supply. As N supply increases, an increasing proportion of N is found in the form of free amino acids, which have a low carbon cost, although proteins remain the main form of N storage. Furthermore, part of the carbon from TNC is incorporated into amino acids and proteins, decreasing the carbon stored as TNC and increasing the carbon stored as amino acids and proteins.

Carbohydrate Metabolism↗

PubMed1997

Effect of heat on cambial reactivation during winter dormancy in evergreen and deciduous conifers.

Responses of cambium to warming were recorded three times (December 14-27, 1990, January 18-February 3 and February 27-March 13, 1991) on 14-year-old Cryptomeria japonica D. Don and four times (December 12-26, 1990, January 18-February 2, February 26-March 12 and March 28-April 13, 1991) on 27-year-old Larix leptolepis Gord., during a period of winter cambial dormancy. Stem surfaces at breast height, mid-tree height and the crown base were warmed to 25-30 degrees C for 2 weeks. After heat treatment, cambia in the treated regions and in untreated regions 1 m above each treated area were examined by optical and transmission electron microscopy (TEM). In C. japonica, heat treatment often resulted in cambial reactivation in the treated regions, and this response to heat gradually increased as the dormant season passed from winter to spring. Conversely, in L. leptolepis, no cell division was observed in the cambial region of warmed stems until natural resumption of cambial activity, which occurred after bud break.

Journal Article↗

PubMed1992

Lattice degeneration of the retina and retinal detachment.

Lattice retinal degeneration is considered the most significant peripheral retinal disorder potentially predisposing to retinal breaks and retinal detachment. Lattice degeneration affects the vitreous and inner retinal layers with secondary changes as deep as the retinal pigment epithelium and perhaps the choriocapillaris. Variations in clinical appearance are the rule; geographically, lattice lesions favor the vertical meridians between the equator and the ora serrata. Lattice degeneration begins early in life and has been reported in sequential generations of the same family. Along with its customary bilateral occurrence, lattice shares other characteristics of a dystrophy. The association between the vitreous and retina in lattice lesions may be responsible for the majority of lattice-induced retinal detachments. The tumultuous event of posterior vitreous separation in the presence of abnormally strong vitreoretinal adherence is the trigger for a retinal tear that, in turn, may lead to retinal detachment. Although retinal holes in young patients with lattice degeneration may play a role in the evolution of retinal detachment, the clinical course of lattice degeneration seems to be one of dormancy rather than of progressive change. This discussion outlines the pathophysiology of lattice retinal degeneration and the relationship of pathophysiology to clinical presentation. The epidemiology of lattice degeneration is summarized, as are the possible precursors to retinal detachment. A clinical characterization of the natural history of lattice degeneration is offered, and interventions for complications are described. To conclude, management strategies from a primary-care standpoint are reviewed.

Cataract Extraction↗

PubMed2001

Localization and targeting of the VP14 epoxy-carotenoid dioxygenase to chloroplast membranes.

Abscisic acid (ABA) is a key regulator of seed dormancy and plant responses to environmental challenges. ABA is synthesized via an oxidative cleavage of 9-cis epoxy-carotenoids, the first committed and key regulatory step in the ABA biosynthetic pathway. Vp14 of maize encodes an epoxy-carotenoid dioxygenase that is soluble when expressed in E. coli. An important goal has been to determine how the soluble VP14 protein is targeted to epoxy-carotenoid substrates that are located in the thylakoid and envelope membranes of chloroplasts and other plastids. Using an in vitro chloroplast import assay, we have shown that VP14 is imported into chloroplasts with cleavage of a short stroma-targeting domain. The mature VP14 exists in two forms, one which is soluble in stroma and the other bound to thylakoid membranes. Analysis of a series of truncated VP14 mutants mapped the membrane targeting signal to the 160 amino acid N-terminal sequence. A putative amphipathic alpha-helix within this region is essential, but not sufficient, for the membrane targeting. Either deletion of or insertion of helix breaking residues into this region abolished the membrane binding, whereas a chimeric protein carrying just the amphipathic region fused with bacterial glutathione S-transferase failed to associate with the thylakoid membrane. The membrane-bound VP14 was partially resistant to chaotropic washes such as 0.1 M Na2CO3 (pH 11.5) and 6 M urea. Unlabelled recombinant VP14 inhibited the tight binding of imported VP14, suggesting that VP14 is associated with specific components of the thylakoid membrane.

Amino Acid Sequence↗

PubMed1990

Dormancy in Peach (Prunus persica L.) Flower Buds : I. Floral Morphogenesis and Endogenous Gibberellins at the End of the Dormancy Period.

Flower buds of peach (Prunus persica L.) trees, cv Novedad de Cordoba (Argentina), were collected near the end of the dormant period and immediately before anthesis. After removal of scale leaves, morphological observations of representative buds, made on transverse and longitudinal microtome sections, showed that all verticils making up the flower are present in an undifferentiated form during the dormant period (June). Flower buds collected at the end of dormant period (August) showed additional growth and differentiation, at which time formation of two ovules was beginning in the unicarpelar gynoecium. Dehiscence of anthers had not yet occurred 10 days before full bloom, and the ovules were still developing. Free endogenous gibberellin (GA)-like substances were quantified by bioassay (Tan-ginbozu dwarf rice microdrop) after SiO(2) partition column chromatography, reversed phase C18-high performance liquid chromatography, and finally Nucleosil [N(CH(3))(2)]high performance liquid chromatography. Bioactive fractions were then subjected to capillary gas chromatography-mass spectrometry-selected ion monitoring (GC-MS-SIM). Gibberellins A(1), A(3), and A(8) were tentatively identified in peach flower buds using GC-SIM and Kovat's retention indices, and relative amounts approximated by GC-SIM (2:8:6 for GA(1), GA(3), and GA(8), respectively). The highest concentration (330 nanograms per gram dry weight) of free GA(1)/GA(3) was found in dormant buds (June) and diminished thereafter. The concentration free of GA(1)/GA(3) did not increase immediately prior to bud break. However, high GA(1)/GA(3) concentrations occurred during stages where rate of growth and cellular differentiation of (mainly fertile) verticils can be influenced.

Journal Article↗

PubMed2005

Role of the Nfo (YqfS) and ExoA apurinic/apyrimidinic endonucleases in protecting Bacillus subtilis spores from DNA damage.

The Bacillus subtilis enzymes ExoA and Nfo (originally termed YqfS) are endonucleases that can repair apurinic/apyrimidinic (AP) sites and strand breaks in DNA. We have analyzed how the lack of ExoA and Nfo affects the resistance of growing cells and dormant spores of B. subtilis to a variety of treatments, some of which generate AP sites and DNA strand breaks. The lack of ExoA and Nfo sensitized spores (termed alpha-beta-) lacking the majority of their DNA-protective alpha/beta-type small, acid-soluble spore proteins (SASP) to wet heat. However, the lack of these enzymes had no effect on the wet-heat resistance of spores that retained alpha/beta-type SASP. The lack of either ExoA or Nfo sensitized wild-type spores to dry heat, but loss of both proteins was necessary to sensitize alpha-beta- spores to dry heat. The lack of ExoA and Nfo also sensitized alpha-beta-, but not wild-type, spores to desiccation. In contrast, loss of ExoA and Nfo did not sensitize growing cells or wild-type or alpha-beta- spores to hydrogen peroxide or t-butylhydroperoxide. Loss of ExoA and Nfo also did not increase the spontaneous mutation frequency of growing cells. exoA expression took place not only in growing cells, but also in the forespore compartment of the sporulating cell. These results, together with those from previous work, suggest that ExoA and Nfo are additional factors that protect B. subtilis spores from DNA damage accumulated during spore dormancy.

Bacillus subtilis↗

PubMed2006

Characterization and mapping of a shattering mutant in rice that corresponds to a block of domestication genes.

Easy shattering reduces yield due to grain loss during harvest in cereals. Shattering is also a hindrance in breeding programs that use wild accessions because the shattering habit is often linked to desirable traits. We characterized a shattering mutant line of rice, Hsh, which was derived from a nonshattering japonica variety, Hwacheong, by N-methyl-N-nitrosourea (MNU) treatment. The breaking tensile strength (BTS) of the grain pedicel was measured using a digital force gauge to evaluate the degree of shattering of rice varieties at 5, 10, 15, 20, 25, 30, 35, and 40 days after heading (DAH). The BTS of Hwacheong did not decrease with increasing DAH, maintaining a level of 180-240 gf, while that of Hsh decreased greatly during 10-20 DAH and finally stabilized at 50 gf. Optical microscopy revealed that Hsh had a well-developed abscission layer similar to the wild rice Oryza nivara (accession IRGC105706), while Hwacheong did not produce an abscission layer, indicating that the shattering of Hsh was caused by differentiation of the abscission layer. On the basis of the BTS value and morphology of the abscission layer of F(1) plants and segregation data in F(2) populations, it was concluded that the easy shattering of Hsh was controlled by the single recessive gene sh-h. The gene sh-h was determined to be located on rice chromosome 7 by bulked segregant analysis. Using 14 SSR markers on rice chromosome 7, the gene sh-h was mapped between the flanking markers RM8262 and RM7161 at distances of 1.6 and 2.0 cM, respectively. An SSR marker Rc17 cosegregated with the gene sh-h. The locus sh-h for shattering was tightly linked to the Rc locus conferring red pericarp, as well as a QTL qSD(s)-7-1 for seed dormancy, implying that this region might represent a domestication block in the evolutionary pathway of rice.

Agriculture↗

PubMed1974

Direct enzymatic repair of deoxyribonucleic acid single-strand breaks in dormant spores.

With the alkaline sucrose gradient centrifugation method, it was found that dormant spores of Clostridium botulinum subjected to 300 krads of gamma radiation showed a distinct decrease in deoxyribonucleic acid (DNA) fragment size, indicating induction of single-strand breaks (SSB). A two- to threefold difference in radiation resistance of spores of two strains of C. botulinum, 33A (37% survival dose [D(37)] = 110 krads) and 51B (D(37) = 47 krads), was accompanied by relatively larger DNA fragments (molecular weight 7.9 x 10(7)) obtained during extraction from the radiation-resistant strain 33A and smaller DNA fragments (molecular weight 1.8 x 10(7)) obtained under identical conditions from radiation-sensitive strain 51B. The apparent number of DNA SSB produced by 300 krads in strains 33A and 51B was 0.37 and 3.50, respectively, per 10(8) daltons of DNA. Addition of 0.02 M ethylenediaminetetraacetic acid (EDTA) to spore suspensions during irradiation doubled the apparent number of SSB in strain 33A but had no effect on strain 51B. In vivo, 0.02 M EDTA present during irradiation to 100 to 300 krads decreased survival of spores of 33A by about 30% but had little or no effect on 51B. Survival of 33A was also reduced by about 45% when the spores were irradiated while frozen in dry ice (-75 C) and, after irradiation, immediately exposed to 0.03 M EDTA for 1 h to inhibit repair in the dormant spores. These results suggest that the highly radiation-resistant strain 33A may be able to accomplish repair of SSB during irradiation or after irradiation under nonphysiological conditions, i.e., in the dormant state. This repair can be inhibited by EDTA. Sedimentation patterns show that DNA from spores of both strains 33A and 51B did not show any postirradiation repair during the first 6 h of germination, as opposed to Bacillus subtilis spores, which exhibit repair immediately after germination. These observations suggest the existence of direct repair in physiological dormant spores of strain 33A in the cryptobiotic resting state in the absence of germination. The repair seems to be similar to that of polynucleotide ligase activity shown to be operative in some vegetative cells. Apparently radiation-sensitive strains such as 51B and B. subtilis are generally poor in DNA repair enzyme activity under conditions of spore dormancy, which may account for the approximately threefold difference in radiation sensitivity or DNA fragility of different strains, or both.

Cell Survival↗