UMLS:C0009443 - FACTA Search

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Query: UMLS:C0009443 (cold)
92,137 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We investigated seasonal patterns of water relations in current-year leaves of three evergreen broad-leaved trees (Ilex pedunculosa Miq., Ligustrum japonicum Thunb., and Eurya japonica Thunb.) with delayed greening in a warm-temperate forest in Japan. We used the pressure-volume method to: (1) assess the extent to which seasonal variation in leaf water relations is attributable to leaf development processes in delayed greening leaves versus seasonal variation in environmental variables; and (2) investigate variation in leaf water relations during the transition from the sapling to the adult tree stage. Leaf mass per unit leaf area was generally lowest just after completion of leaf expansion in May (late spring), and increased gradually throughout the year. Osmotic potential at full turgor (Psi(o) (ft)) and leaf water potential at the turgor loss point (Psi(w) (tlp)) were highest in May, and lowest in midwinter in all species. In response to decreasing air temperature, Psi(o) (ft) dropped at the rate of 0.037 MPa degrees C(-1). Dry-mass-based water content of leaves and the symplastic water fraction of total leaf water content gradually decreased throughout the year in all species. These results indicate that reductions in the symplastic water fraction during leaf development contributed to the passive concentration of solutes in cells and the resulting drop in winter Psi(o) (ft). The ratio of solutes to water volume increased in winter in current-year leaves of L. japonicum and E. japonica, indicating that osmotic adjustment (active accumulation of solutes) also contributed to the drop in winter in Psi(o) (ft). Bulk modulus of elasticity in cell walls fluctuated seasonally, but no general trend was found across species. Over the growing season, Psi(o) (ft) and Psi(w) (tlp) were lower in adult trees than in saplings especially in the case of I. pedunculosa, suggesting that adult-tree leaves are more drought and cold tolerant than sapling leaves. The ontogenetic increase in the stress resistance of I. pedunculosa may be related to its characteristic life form because I. pedunculosa grows taller than the other species studied.
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PMID:Seasonal variations in water relations in current-year leaves of evergreen trees with delayed greening. 1665 Dec 52

Plasma membrane alterations in two tuber-bearing potato species during a 20-day cold acclimation period were investigated. Leaf-callus tissues of the frost-resistant Solanum acaule Hawkes ;Oka 3878' and the frost-susceptible, commonly grown Solanum tuberosum ;Red Pontiac,' were used. The former is a species that can be hardened after subjecting to the low temperature, and the latter does not harden. Samples for the electron microscopy were prepared from callus cultures after hardening at 2 C in the dark for 0, 5, 10, 15, and 20 days. After 20 days acclimation, S. acaule increased in frost hardiness from -6 to - 9 C (killing temperature), whereas frost hardiness of S. tuberosum remained unchanged (killed at -3 C). Actually, after 15 days acclimation, a -9 C frost hardiness level in S. acaule callus cultures had been achieved.Membrane protein particle aggregation was monitored using freeze-fracture electron microscopy. Protein particles were aggregated in S. acaule up to 10 days after the initiation of acclimation treatment and then redistributed almost to the level of control after 15 days. No such changes were observed for S. tuberosum under similar experimental conditions. The change in protein particle aggregation pattern in S. acaule is interpreted as indicating the presence of an adaptive fluidity control mechanism in that species.
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PMID:Plasma Membrane Alterations in Callus Tissues of Tuber-bearing Solanum Species during Cold Acclimation. 1666 98

Cold temperature acclimation in strawberry (Fragaria virginiana) leaves apparently involves the alteration of cellular osmotic properties. Alterations in leaf osmotic potential were closely correlated with alterations in soluble carbohydrate content of the leaf tissue and changing temperatures. Leaf starch content was inversely related to soluble carbohydrate levels, suggesting that starch is a partial source of osmoticum during osmotic adjustment associated with cold temperature stress. Free amino acid changes were more closely linked to senescence and growth processes while changes in ion content suggested a rapid mobilization of solutes at the onset of freezing temperatures. This was supported by changes in whole plant gradients in leaf osmotic potential before and after exposure to freezing temperatures. In terms of freezing resistance and the role of osmotic adjustment in the development of resistance, it was found that of all leaves undergoing osmotic adjustment only the younger leaves survived, suggesting an age-dependent component to freezing resistance in leaves. Freezing resistance appears to involve alterations in several cellular properties that act in concert to confer a hardy state of the tissue. Although osmotic adjustment may be an important component of the final combination of cellular properties, this study indicates that solute accumulation does not function alone to confer freezing resistance.
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PMID:Osmotic Adjustment and the Development of Freezing Resistance in Fragaria virginiana. 1666 42

Spinach (Spinacia oleracea L.) seedlings, grown in soil or on an agar medium in vitro, became cold acclimated when exposed to a constant 5 degrees C. Plants subjected to cold acclimation, beginning 1 week postgermination, attained freezing tolerance levels similar to that achieved by seedlings that were cold acclimated beginning 3 weeks after sowing. Seedlings at 1 week of age had only cotyledonary leaves, while 3-week-old seedlings had developed true leaves. Plants grown in vitro were able to increase in freezing tolerance, but were slightly less hardy than soil-grown plants. These results suggest that spinach, a cool-season crop that begins growth in early spring when subzero temperatures are likely, can undergo cold acclimation at the earliest stages of development following germination. Axenic seedlings, grown in vitro, were used to develop a noninjurious radiolabeling technique. Leaf proteins were radiolabeled to specific activities of 10(5) counts per minute per microgram at 25 degrees C or 5 x 10(4) counts per minute per microgram at 5 degrees C over a 24 hour period. The ability to radiolabel leaf proteins of in vitro grown plants to high specific activities at low temperature, without injury or microbial contamination, will facilitate studies of cold acclimation.
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PMID:Induction of Freezing Tolerance in Spinach during Cold Acclimation. 1666 35

Spinach (Spinacia oleracea L. cv Bloomsdale) seedlings cultured in vitro were used to study changes in protein synthesis during cold acclimation. Seedlings grown for 3 weeks postsowing on an inorganic-nutrient-agar medium were able to increase their freezing tolerance when grown at 5 degrees C. During cold acclimation at 5 degrees C and deacclimation at 25 degrees C, the kinetics of freezing tolerance induction and loss were similar to that of soil-grown plants. Freezing tolerance increased after 1 day of cold acclimation and reached a maximum within 7 days. Upon deacclimation at 25 degrees C, freezing tolerance declined within 1 day and was largely lost by the 7th day. Leaf proteins of intact plants grown at 5 and 25 degrees C were in vivo radiolabeled, without wounding or injury, to high specific activities with [(35)S]methionine. Leaf proteins were radiolabeled at 0, 1, 2, 3, 4, 7, and 14 days of cold acclimation and at 1, 3, and 7 days of deacclimation. Up to 500 labeled proteins were separated by two-dimensional gel electrophoresis and visualized by fluorography. A rapid and stable change in the protein synthesis pattern was observed when seedlings were transferred to the low temperature environment. Cold-acclimated leaves contained 22 polypeptides not found in nonacclimated leaves. Exposure to 5 degrees C induced the synthesis of three high molecular weight cold acclimation proteins (CAPs) (M(r) of about 160,000, 117,000, and 85,000) and greatly increased the synthesis of a fourth high molecular weight protein (M(r) 79,000). These proteins were synthesized during day 1 and throughout the 14 day exposure to 5 degrees C. During deacclimation, the synthesis of CAPs 160, 117, and 85 was greatly reduced by the first day of exposure to 25 degrees C. However, CAP 79 was synthesized throughout the 7 day deacclimation treatment. Thus, the induction at low temperature and termination at warm temperature of the synthesis of CAPs 160, 117, and 85 was highly correlated with the induction and loss of freezing tolerance. Cold acclimation did not result in a general posttranslational modification of leaf proteins. Most of the observed changes in the two-dimensional gel patterns could be attributed to the de novo synthesis of proteins induced by low temperature. In spinach leaf tissue, heat shock altered the pattern of protein synthesis and induced the synthesis of several heat shock proteins (HSPs). One polypeptide synthesized in cold-acclimated leaves had a molecular weight and net charge (M(r) 79,000, pI 4.8) similar to that of a HSP (M(r) 83,000, pI 4.8). However, heat shock did not increase the freezing tolerance, and cold acclimation did not increase heat tolerance over that of nonacclimated plants, but heat-shocked leaf tissue was more tolerant to high temperatures than nonacclimated or cold-acclimated leaf tissue. When protein extracts from heat-shocked and cold-acclimated leaves were mixed and separated in the same two-dimensional gel, the CAP and HSP were shown to be two separate polypeptides with slightly different isoelectric points and molecular weights.
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PMID:Induction of freezing tolerance in spinach is associated with the synthesis of cold acclimation induced proteins. 1666 36

The objective of this research was to develop a system in which the direction of fructan metabolism could be controlled. Three-week-old wheat seedlings (Triticum aestivum L. cv Caldwell) grown at 25 degrees C were transferred to cold temperature (10 degrees C) to induce fructan synthesis and then were transferred to continuous darkness at 25 degrees C after defoliation and fructan degradation monitored. The total fructan content increased significantly 1 day after transferring from 25 degrees C to 10 degrees C in both leaf blades and the remainder of the shoot tissue, 90% of which was leaf sheath tissue. Leaf sheaths contained higher concentrations of fructan and greater portions of high molecular weight fructan than did leaf blades. Fructan content in leaf sheaths declined rapidly and was gone completely within 48 hours following transfer to 25 degrees C in darkness. In leaf blades the invertase activity fluctuated during cold treatment. The activity of sucrose:sucrose fructosyl transferase increased markedly during cold treatment, while fructan hydrolase activity decreased slightly. In leaf sheaths, however, the activity of invertase decreased rapidly upon transfer to cold temperature and remained low. Trends in sucrose:sucrose fructosyl transferase and hydrolase activity in sheaths were the same as those of leaf blades. Sheath invertase and hydrolase activity increased when plants were transferred back to darkness at 25 degrees C, while sucrose:sucrose fructosyl transferase activity decreased. These results indicate that changing leaf sheath temperature can be utilized to control the direction of fructan metabolism and thus provide a system in which the synthesis or degradation of fructan can be examined.
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PMID:Fructan metabolism in wheat in alternating warm and cold temperatures. 1666 99

To gain a better understanding of the mechanism of cold induced sweetening, sugar accumulation in potato, Solanum tuberosum cv Bintje, was compared to the maximum activity of inorganic pyrophosphate (PPi):fructose 6-phosphate 1-phosphotransferase (EC 2.7.1.90) and the concentration of two regulatory metabolites. Mature tubers accumulated reducing sugars and sucrose at an almost linear rate of 13.4 and 5.2 micromole per day per gram dry weight at 2 degrees C and 4.5 and 1.3 micromole per day per gram dry weight, respectively, at 4 degrees C. During storage at 8 degrees C sugar accumulation was nil. Sugar accumulation was preceded by a lag phase of about 4 days. The accumulation of reducing sugars persisted for at least 4 weeks, whereas sucrose accumulation declined after 2 weeks of storage. The ratio of glucose:fructose changed concomitantly with sugar increase from 65:35 to equimolarity. The maximum activity of PPi:fructose 6-phosphate 1-phosphotransferase was 2.51 and 2.25 units per gram dry weight during storage at 2 and 8 degrees C, respectively. The temperature coefficient of this enzyme from potatoes kept at 2 or 8 degrees C was 2.12 and 2.48, respectively. The endogenous concentration of fructose 2,6-biphosphate increased from 0.15 to 1 nanomole per gram dry weight during storage at 2 and 4 degrees C but remained the same throughout storage at 8 degrees C. After exposure to 2 degrees C an initial increase in the concentration of PPi was observed from 4.0 to 5.6 nanomoles per gram dry weight. Pyrophosphate concentration did not change during storage at 4 degrees C but decreased slightly at 8 degrees C. All observed changes became annulled after transfer of cold stored tubers to 18 degrees C. These data strongly indicate that PPi:fructose 6-phosphate 1-phosphotransferase can be fully operational in cold stored potato tubers and the lack of increase in PPi concentration supports the functioning of this enzyme during sugar accumulation.
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PMID:Potential Role of Pyrophosphate:Fructose 6-Phosphate Phosphotransferase in Carbohydrate Metabolism of Cold Stored Tubers of Solanum tuberosum cv Bintje. 1666 18

Responses of cortical microtubules in spinach (Spinacia oleracea L. cv Bloomsdale) mesophyll cells to freezing, thawing, supercooling, and dehydration were assessed. Microtubules were visualized using a modified procedure for indirect immunofluorescence microscopy. Leaf sections of nonacclimated and cold-acclimated spinach were slowly frozen to various temperatures, fixed while frozen, and microtubules immunolabelled. Both nonacclimated and cold-acclimated cells exhibited nearly complete microtubule depolymerization after ice formation. After 1 hour thawing at 23 degrees C, microtubules in both nonacclimated and cold-acclimated cells repolymerized. With time, however, microtubules in nonacclimated cells again depolymerized. Since microtubules in cells of leaf tissue frozen slowly are subjected to dehydration as well as subzero temperatures, these stresses were applied separately and their effects on microtubules noted. Supercooling induced microtubule depolymerization in both nonacclimated and cold-acclimated cells, but to a smaller extent than did freezing. Exposing leaf sections to solutions of sorbitol (a cell wall-penetrating osmoticum) or polyethylene glycol 10,000 (a nonpenetrating osmoticum) at room temperature caused microtubule depolymerization. The effects of low temperature and dehydration are roughly additive in producing the observed microtubule responses during freezing. Only small differences in microtubule stability were resolved between nonacclimated and cold-acclimated cells.
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PMID:Microtubules in mesophyll cells of nonacclimated and cold-acclimated spinach : visualization and responses to freezing, low temperature, and dehydration. 1666 66

Freezing, dehydration, and supercooling cause microtubules in mesophyll cells of spinach (Spinacia oleracea L. cv Bloomsdale) to depolymerize (ME Bartolo, JV Carter, Plant Physiol [1991] 97: 175-181). The objective of this study was to determine whether the LT(50) (lethal temperature: the freezing temperature at which 50% of the tissue is killed) of spinach leaf tissue can be changed by diminishing the extent of microtubule depolymerization in response to freezing. Also examined was how tolerance to the components of extracellular freezing, low temperature and dehydration, is affected by microtubule stabilization. Leaf sections of nonacclimated and cold-acclimated spinach were treated with 20 micromolar taxol, a microtubule-stabilizing compound, prior to freezing, supercooling, or dehydration. Taxol stabilized microtubules against depolymerization in cells subjected to these stresses. When pretreated with taxol both nonacclimated and cold-acclimated cells exhibited increased injury during freezing and dehydration. In contrast, supercooling did not injure cells with taxol-stabilized microtubules. Electrolyte leakage, visual appearance of the cells, or a microtubule repolymerization assay were used to assess injury. As leaves were cold-acclimated beyond the normal period of 2 weeks taxol had less of an effect on cell survival during freezing. In leaves acclimated for up to 2 weeks, stabilizing microtubules with taxol resulted in death at a higher freezing temperature. At certain stages of cold acclimation, it appears that if microtubule depolymerization does not occur during a freeze-thaw cycle the plant cell will be killed at a higher temperature than if microtubule depolymerization proceeds normally. An alternative explanation of these results is that taxol may generate abnormal microtubules, and connections between microtubules and the plasma membrane, such that normal cellular responses to freeze-induced dehydration and subsequent rehydration are blocked, with resultant enhanced freezing injury.
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PMID:Effect of microtubule stabilization on the freezing tolerance of mesophyll cells of spinach. 1666 67

Freezing, dehydration, and supercooling cause microtubules in mesophyll cells of spinach (Spinacia oleracea L. cv Bloomsdale) to depolymerize (ME Bartolo, JV Carter [1991] Plant Physiol 97: 175-181). The objective of this study was to gain insight into the question of whether microtubules depolymerize as a direct response to environmental stresses or as an indirect response to cellular changes that accompany the stresses. Leaf sections of spinach were treated with Li(+) before and during exposure to low temperature. Treatment with Li(+) decreased the amount of microtubule depolymerization in cells subjected to low temperature, relative to a nontreated control, raising the possibility that the microtubules in these cells may not be inherently cold labile. Rather, microtubule depolymerization may be in response to cold-induced changes in concentration of cytoplasmic components.
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PMID:Lithium decreases cold-induced microtubule depolymerization in mesophyll cells of spinach. 1666

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