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PubMed1987

Isolation and in vitro translation of polysomes from mature rye leaves.

Cytoplasmic polysomes have been prepared from mature leaves of winter rye (Secale cereale L. cv Puma). This is the first time a method has been developed for isolation of highly polymerized polysomes from mature leaves. The degree of intactness of isolated plant polysomes has been determined by two independent but complementary methods: size class distribution by sucrose gradient centrifugation and in vitro translation. The polymerization of isolated polysomes was estimated by the ratio of the proportion of large polysomes to the proportion of small polysomes obtained from the profiles. Our results show that the composition of the optimal polysome isolation buffer for mature rye leaves is different from that reported for young tobacco and pea leaves. Polysomes were translated in vitro with the S-105 wheat germ fraction. The degree of polysome polymerization has a significant effect on their in vitro translation since both the incorporation of amino acid and the presence of high molecular weight polypeptides are proportional to the large polysomes/small polysomes ratio. This study emphasizes the need to evaluate isolation conditions carefully before proceeding with polysome studies in any particular tissue or in tissues under different physiological status.

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PubMed1987

The Mechanics of Injury to Isolated Protoplasts following Osmotic Contraction and Expansion.

Micro-osmotic manipulation was used to determine the influence of osmotic contraction on the expansion potential of individual protoplasts isolated from rye (Secale cereale L. cv Puma) leaves. For protoplasts isolated from leaves of nonacclimated plants (NA protoplasts), osmotic contraction in sufficiently hypertonic solutions (>1.53 osmolal) predisposed the protoplasts to lysis during osmotic expansion when they were returned to isotonic conditions (0.53 osmolal). In contrast, for protoplasts isolated from leaves of cold acclimated plants (ACC protoplasts), osmotic contraction in either 2.6 or 4.0 osmolal solutions was readily reversible. Following osmotic contraction, the resting tension (gamma(r)) of NA protoplasts was similar to that determined for protoplasts in isotonic solutions (i.e. 110 +/- 22 micronewtons per meter). In contrast, gamma(r) of ACC protoplasts decreased from 164 +/- 27 micronewtons per meter in isotonic solutions to values close to zero in hypertonic solutions. Following expansion in hypotonic solutions, gamma(r)'s of both NA and ACC protoplasts were similar for area expansions over the range of 1.3 to 1.6. Following osmotic contraction and reexpansion of NA protoplasts, hysteresis was observed in the relationship between gamma(r) and surface area-with higher values of gamma(r) at a given surface area. In contrast, no hysteresis was observed in this relationship for ACC protoplasts. Direct measurements of plasma membrane tension (gamma) during osmotic expansion of NA protoplasts from hypertonic solutions (1.53 osmolal) revealed that gamma increased rapidly after small increments in surface area, and lysis occurred over a range of 1.2 to 8 millinewtons per meter. During osmotic expansion of ACC protoplasts from hypertonic solutions (2.6 osmolal), there was little increase in gamma until after the isotonic surface area was exceeded. These results are discussed in relation to the differences in the behavior of the plasma membrane of NA and ACC protoplasts during osmotic contraction (i.e. endocytotic vesiculation versus exocytotic extrusion) and provide a mechanistic interpretation to account for the differential sensitivity of NA and ACC protoplasts to osmotic expansion from hypertonic solutions.

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PubMed1987

Low Temperature Development Induces a Specific Decrease in trans-Delta-Hexadecenoic Acid Content which Influences LHCII Organization.

Lipid and fatty acid analyses were performed on whole leaf extracts and isolated thylakoids from winter rye (Secale cereale L. cv Puma) grown at 5 degrees C cold-hardened rye (RH) and 20 degrees C nonhardened rye (RNH). Although no significant change in total lipid content was observed, growth at low, cold-hardening temperature resulted in a specific 67% (thylakoids) to 74% (whole leaves) decrease in the trans-Delta(3)-hexadecenoic acid (trans-16:1) level associated with phosphatidyldiacylglycerol (PG). Electron spin resonance and differential scanning calorimetry (DSC) indicated no significant difference in the fluidity of RH and RNH thylakoids. Separation of chlorophyll-protein complexes by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that the ratio of oligomeric light harvesting complex:monomeric light harvesting complex (LHCII(1):LHCII(3)) was 2-fold higher in RNH than RH thylakoids. The ratio of CP1a:CP1 was also 1.5-fold higher in RNH than RH thylakoids. Analyses of winter rye grown at 20, 15, 10, and 5 degrees C indicated that both, the trans-16:1 acid levels in PG and the LHCII(1):LHCII(3) decreased concomitantly with a decrease in growth temperature. Above 40 degrees C, differential scanning calorimetry of RNH thylakoids indicated the presence of five major endotherms (47, 60, 67, 73, and 86 degrees C). Although the general features of the temperature transitions observed above 40 degrees C in RH thylakoids were similar to those observed for RNH thylakoids, the transitions at 60 and 73 degrees C were resolved as inflections only and RH thylakoids exhibited transitions at 45 and 84 degrees C which were 2 degrees C lower than those observed in RNH thylakoids. Since polypeptide and lipid compositions of RH and RNH thylakoids were very similar, we suggest that these differences reflect alterations in thylakoid membrane organization. Specifically, it is suggested that low developmental temperature modulates LHCII organization such that oligomeric LHCII predominates in RNH thylakoids whereas a monomeric or an intermediate form of LHCII predominates in RH thylakoids. Furthermore, we conclude that low developmental temperature modulates LHCII organization by specifically altering the fatty composition of thylakoid PG.

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PubMed1987

Development at Cold-Hardening Temperatures : The Structure and Composition of Purified Rye Light Harvesting Complex II.

Light harvesting complex II (LHCII) was purified from cold-hardened (RH) and nonhardened winter rye (RNH) (Secale cereale L. cv Puma) employing a modified procedure of JJ Burke, CL Ditto, CJ Arntzen (Arch Biochem Biophys 187: 252-263). Triton X-100 solubilization of thylakoid membranes followed by three successive precipitations with 100 mm KCl and 10 mm MgCl(2) resulted in yields of up to 25% on a chlorophyll (Chl) basis and a purity of 90 to 95%, based on polypeptide analysis within 4 hours. Polypeptide and pigment analyses, 77 K fluorescence emission and room temperature absorption spectra indicate the LHCII obtained by this modified method is comparable to LHCII obtained by other published methods. Comparison of purified RH and RNH LHCII indicated no significant differences with respect to polypeptide, amino acid, Chl, and carotenoid compositions as well as no differences in lipid content. However, RH LHCII differed from RNH LHCII specifically with respect to the fatty acid composition of phosphatidyldiacylglycerol only. RH LHCII exhibited a 54% lower trans-Delta(3)-hexadecenoic acid level associated with PG and a 60% lower oligomeric LHCII:monomeric LHCII (LHCII(1):LHCII(3)) than RNH LHCII. Both RH and RNH LHCII exhibited a 5-fold enrichment in PG specifically. Complete removal of PG by enzymic hydrolysis resulted in a significant reduction in the oligomeric content of both RH and RNH LHCII such that LHCII(1):LHCII(3) of RH and RNH LHCII preparations were the same. This confirms that this specific compositional change accounts for the structural differences between RH and RNH LCHII observed in situ and in vitro.

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PubMed1987

Early and late heat shock proteins in wheats and other cereal species.

Coleoptiles and roots of 3-day-old seedlings from five cereal species (Triticum aestivum L., T. durum Desf., Hordeum vulgare L., Secale cereale L., and Triticale) respond to heat shock at 40 degrees C by synthesizing a new set of 13 strong bands (as revealed by one-dimensional sodium dodecyl sulfate gel electrophoresis) as well as some 20 degrees C proteins. Heat shock proteins (HSPs) belong to three different size groups: high molecular mass HSPs in the 103 to 70 kilodalton range, intermediate molecular mass HSPs in the 62 to 32 kilodalton range, and low molecular mass HSPs about 17 to 16 kilodalton in size. At the beginning of the heat shock coleoptiles show a reduced ability to synthesize intermediate molecular mass HSPs but after 4 hours at 40 degrees C they exhibit fully developed HSP patterns identical to that found in roots. Synthesis of early HSPs declines after 7 hours of treatment followed by the appearance of a new set of 12 protein bands (late HSPs) in the ranges 99 to 83, 69 to 35, and 15 to 14 kilodaltons. After 12 hours at 40 degrees C, three other late HSPs of 89, 45, and 38 kilodalton are induced. The induction of late HSPs after 7 hours at 40 degrees C appears to be associated with an enhancement of radioactive methionine incorporation into proteins.

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PubMed1987

Polysomes from winter rye seedlings grown at low temperature : I. Size class distribution, composition, and stability.

We have studied the influence of growth at low temperature on size class distribution, stability and composition of leaf cytoplasmic polysomes from rye seedlings (Secale cereale, cv Puma) grown at 5 degrees C and at 20 degrees C. Leaves of seedlings grown at 5 degrees C contain 2.7 times more cytoplasmic polysomes (expressed on a DNA basis) and the polysome size class distribution is skewed toward larger polysomes. These changes were more pronounced in the free polysome fraction than in the membrane-bound fraction. The melting point of the total ribosome fraction from cold-grown leaves was decreased by 3.7 degrees C. Electrophoresis did not reveal any difference in the rRNA or in core-ribosomal proteins (KCl nondissociable) following growth at low temperature. Some differences were noted in peripheral ribosomal proteins. This study is the first to examine the effect of growth at low and high temperatures on polysome metabolism using plants of similar developmental stage. Polysome quantity, polymerization, melting point and peripheral ribosomal proteins in rye seedlings are modified during growth at low temperature.

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PubMed1988

Modifications of Sulfhydryl Groups on Phytochrome and Their Influence on Physicochemical Differences between the Red- and Far-Red-Absorbing Forms.

Phytochrome extracted from shoots of dark-grown rye (Secale cereale cv Rymin) and oat (Avena sativa cv Garry) as the far-red-form (Pfr) and/or under conditions conducive to oxidation exhibited a blue shift in the visible absorption maximum of its red-light-absorbing form (Pr) relative to that measured in vivo. This spectral alteration could not be reversed but could be prevented by inclusion of 10 millimolar diethyldithiocarbamate and 140 millimolar 2-mercaptoethanol in homogenization buffers. Similar blue shifts were induced in purified rye phytochrome by addition of the sulfhydryl-modifying reagent, 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB). In spectrally normal phytochrome (i.e., no detectable blue shift), Pfr had three to four more sulfhydryls available for rapid reaction with DTNB than did Pr. This difference was maintained over a 2.5-hour time course. Phytochrome purified under conditions resulting in a blue-shifted Pr absorption maximum exhibited a decreased short-term reactivity of Pfr to DTNB. Comparison of the binding and elution of altered and unaltered phytochrome from agarose-immobilized Cibacron blue 3GA confirmed that the Pfr form of spectrally normal phytochrome had a greater affinity for the dye than did the Pr form but that spectral alteration of phytochrome was accompanied by a loss of this difference as evidenced by an increased binding of Pr to the dye. It was concluded that phytochrome has highly reactive sulfhydryl residues located on the portion of the protein that undergoes conformational changes on interconversion of Pr and Pfr and that these residues require rigorous protection in order to extract the native form of the protein from plant tissue.

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PubMed1988

A comparative spin-label study of isolated plasma membranes and plasma membranes of whole cells and protoplasts from cold-hardened and nonhardened winter rye.

Lipid-lipid and lipid-protein interactions in the plasma membranes of whole cells and protoplasts and an isolated plasma membrane fraction from winter rye (Secale cereale L. cv Puma) have been studied by spin labeling. Spectra were recorded between -40 degrees C and 40 degrees C using the freely diffusing spin-label, 16-doxyl stearic acid, as a midbilayer membrane probe. The probe was reduced by the whole cells and protoplasts and reoxidized by external potassium ferricyanide. The reoxidized probe was assumed to be localized in the plasma membrane. The spectra consisted of the superposition of a narrow and a broad component indicating that both fluid and immobilized lipids were present in the plasma membrane. The two components were separated by digital subtraction of the immobilized component. Temperature profiles of the membranes were developed using the percentage of immobilized lipid present at each temperature and the separation between the outermost hyperfine lines for the fluid lipid component. Lipid immobilization was attributed to lipid-protein interactions, lipid-cell wall interactions, and temperature-induced lipid phase transitions to the gel-state. Temperature profiles were compared for both cold-hardened and nonhardened protoplasts, plasma membranes, and plasma membrane lipids, respectively. Although cold-hardening extended the range of lipid fluidity by 5 degrees C, it had no effect on lipid-protein interactions or activation energies of lipid mobility. Differences were found, however, between the temperature profiles for the different samples, suggesting that alterations in the plasma membrane occurred as a consequence of the isolation methods used.

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PubMed1989

Low Temperature-Induced Decrease in trans-Delta-Hexadecenoic Acid Content Is Correlated with Freezing Tolerance in Cereals.

The effect of growth at 5 degrees C on the trans-Delta(3)-hexadecenoic acid content of phosphatidyl(d)glycerol was examined in a total of eight cultivars of rye (Secale cereale L.) and what (Triticum aestivum L.) of varying freezing tolerance. In these monocots, low temperature growth caused decreases in the trans-Delta(3)-hexadecenoic acid content of between 0 and 74% with concomitant increases in the palmitic acid content of phosphatidyl(d)glycerol. These trends were observed for whole leaf extracts as well as isolated thylakoids. The low growth temperature-induced decrease in the trans-Delta(3)-hexadecenoic acid content was shown to be a linear function (r(2) = 0.954) of freezing tolerance in these cultivars. Of the six cold tolerant dicotyledonous species examined, only Brassica and Arabidopsis thaliana L. cv Columbia exhibited a 42% and 65% decrease, respectively, in trans-Delta(3)-hexadecenoic acid content. Thus, the relationship between the change in trans-Delta(3)-hexadecenoic acid content of phosphatidyl(d)glycerol and freezing tolerance cannot be considered a general one for all cold tolerant plant species. However, species which exhibited a low growth temperature-induced decrease in trans-Delta(3)-hexadecenoic acid also exhibited a concomitant shift in the in vitro organization of the light harvesting complex II from a predominantly oligomeric form to the monomeric form. We conclude that the proposed role of phosphatidyl(d)glycerol in modulating the organization of light harvesting complex II as a function of growth temperature manifests itself to varying degrees in different plant species. A possible physiological role for this phenomenon with respect to low temperature acclimation and freezing tolerance in cereals is discussed.

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PubMed1989

Differences in the Anaerobic Lactate-Succinate Production and in the Changes of Cell Sap pH for Plants with High and Low Resistance to Anoxia.

Anaerobically treated seedlings of Oryza sativa L. var arborio accumulated in their shoots more succinate than lactate and cell sap became alkaline. Conversely, in Triticum aestivum L. var MEK 86 lactate accumulation was far higher than that of succinate and cell sap was acidified. Anoxia clearly induced proton consumption in both species as an important means to prevent or counteract acidosis. Other species studied were: Echinochloa crus-galli L. Beauv., Zea mays L. var De Kalb XL75, Secale cereale L. var primizia and Hordeum vulgare L. var rondo. Changes in cell sap pH and succinate to lactate ratios distinguished resistant from nonresistant species.

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PubMed1989

Red light-induced accumulation of ubiquitin-phytochrome conjugates in both monocots and dicots.

Phytochrome is rapidly degraded in vivo after photoconversion from the stable red-absorbing (Pr) form to the far red-absorbing (Pfr) form. Previously, we have shown in etiolated oat seedlings that ubiquitin-phytochrome conjugates (Ub-P) appear after Pfr formation suggesting that oat phytochrome is rapidly degraded by a ubiquitin-dependent proteolytic pathway. Here, we extend this observation to etiolated tissue from other monocotyledonous (corn [Zea mays. (L.)] and rye [Secale cereale (L.)] and dicotyledonous species (pea [Pisum sativum (L,)] and zucchini squash [Cucurbita pepo (L.)]). Following Pfr formation by red light, all four species synthesized a heterogeneous series of Ub-P that appeared and disappeared concomitant with the degradation of the chromoprotein. When Pfr was photoconverted back to Pr by a far-red light pulse, degradation of phytochrome ceased and the levels of Ub-P concomitantly dropped. In pea and zucchini squash, loss of Ub-P after photoconversion of Pfr back to Pr was rapid, occurring with a half-life of approximately 5 to 10 minutes. These data indicate that the accumulation of Ub-P after Pfr formation is a general phenomenon in etiolated seedlings of higher plants and further support the hypothesis that plants degrade Pfr via Ub-P intermediates.

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PubMed1989

Anaerobic induction of alanine aminotransferase in barley root tissue.

Alanine aminotransferase, otherwise called glutamate-pyruvate aminotransferase (GPT), activity increases up to fourfold during several days of anaerobic induction in barley (Hordeum vulgare L.) roots, reaching a maximum activity of 13 international units per gram fresh weight. This increase in activity paralleled the increase in alcohol dehydrogenase activity in the same root tissue. Upon return to aerobic conditions, the induced GPT activity declined with an apparent half-life of 2 days. The isozyme profile of GPT in barley root tissue comprised one band of activity; in maize there were three bands of activity, the bands with greater mobility had much lower activity. Native polyacrylamide gel electrophoresis indicated that the induction of GPT activity results from an increase in the level of activity of these bands; no other activities were detected. When root tissue was induced under different levels of hypoxia (0%, 2%, 5%, and 21% O(2)), changes in GPT activity were found to increase with lower levels of oxygen. Comparisons of GPT induction in barley, maize (Zea mays), rye, (Secale cereale) and wheat (Triticum aestivum) indicate that this enzyme is induced in the root tissue of all of these cereals; however, anaerobic root conditions do not result in the induction of GPT activity in leaf tissue. The dependence of GPT induction on high levels of nitrate in the media was tested by comparing activity levels in Hoagland solution and a nitrate-free nutrient solution. GPT activity was induced to similar levels under both conditions. These results indicate that alanine aminotransferase shows a very similar pattern of induction to alcohol dehydrogenase in barley root tissue and may be important in anaerobic glycolysis.

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PubMed1989

Effect of cold acclimation on the incidence of two forms of freezing injury in protoplasts isolated from rye leaves.

The freezing tolerance and incidence of two forms of freezing injury (expansion-induced lysis and loss of osmotic responsiveness) were determined for protoplasts isolated from rye leaves (Secale cereale L. cv Puma) at various times during cold acclimation. During the first 4 weeks of the cold acclimation period, the LT(50) (i.e. the minimum temperature at which 50% of the protoplasts survived) decreased from -5 degrees C to -25 degrees C. In protoplasts isolated from nonacclimated leaves (NA protoplasts), expansion-induced lysis (EIL) was the predominant form of injury at the LT(50). However, after only 1 week of cold acclimation, the incidence of EIL was reduced to less than 10% at any subzero temperature; and loss of osmotic responsiveness was the predominant form of injury, regardless of the freezing temperature. Fusion of either NA protoplasts or protoplasts isolated from leaves of seedlings cold acclimated for 1 week (1-week ACC protoplasts) with liposomes of dilinoleoylphosphatidylcholine also decreased the incidence of EIL to less than 10%. Fusion of protoplasts with dilinoleoylphosphatidylcholine diminished the incidence of loss of osmotic responsiveness, but only in NA protoplasts or 1-week ACC protoplasts that were frozen to temperatures over the range of -5 to -10 degrees C. These results suggest that the cold acclimation process, which results in a quantitative increase in freezing resistance, involves several different qualitative changes in the cryobehavior of the plasma membrane.

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PubMed1989

Parallel effects of freezing and osmotic stress on the ATPase activity and protein composition of the plasma membrane of winter rye seedlings.

The objective of this study was to determine the influence of freezing versus hypertonic stress on the ATPase activity and polypeptide profile of the plasma membrane of nonacclimated winter rye leaves (Secale cereale L. cv Puma). Exposure of leaves to hypertonic sorbitol solutions resulted in a similar extent of injury as did freezing to subzero temperatures that resulted in equivalent osmotic stresses. When isolated with a two-phase partition system of aqueous polymers, the plasma membrane fractions of control, frozen, or hypertonically stressed leaves were of similar purity as judged by the distribution of marker enzyme activities. When assayed in the presence of Triton X-100 (0.05% w/w), ATPase activity was decreased only slightly in plasma membrane fractions isolated from either frozen or hypertonically stressed leaves. In contrast, the specific ATPase activity of the plasma membrane fractions assayed in the absence of Triton X-100 increased following freezing or hypertonic stress. As a result, the Triton X-100 stimulation of the ATPase activity decreased significantly from sixfold in control leaves to threefold in lethally stressed leaves and reflects an increase in the permeability of the plasma membrane vesicles. The increased permeability was also manifested as a decrease in H(+)-transport following exposure to freezing or hypertonic stress. Both freezing and hypertonic exposure at subzero temperatures altered the polypeptide profile of the plasma membrane, but with the exception of one polypeptide, there was no difference between the two treatments.

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PubMed1990

Cryopreservation of rye protoplasts by vitrification.

A procedure has been developed for the vitrification of mesophyll protoplasts isolated from leaves of nonacclimated (NA) and cold-acclimated (ACC) winter rye seedlings (Secale cereale L. cv Puma). The procedure involves (a) equilibration (loading) of the protoplasts with an intermediate concentration (1.5, 1.75, or 2.0 molar) of ethylene glycol (EG) at 20 degrees C; (b) dehydration of the protoplasts in a concentrated vitrification solution made of 7 molar EG + 0.88 molar sorbitol + 6% (w/v) bovine serum albumin (BSA) at 0 degrees C; (c) placing the protoplasts into polypropylene straws and quenching in liquid nitrogen (LN(2)); and (d) recovery of the protoplasts from LN(2) and removal (unloading) of the vitrification solution. For NA protoplasts, 47 + 1% survival was obtained following recovery from LN(2) if the protoplasts were first loaded with 1.75 molar EG prior to the dehydration step. However, to achieve this level of survival, NA protoplasts had to be unloaded in a hypertonic (2.0 osmolal [osm]) sorbitol solution. If they were unloaded in an isotonic solution (0.53 osm), survival was 3+/-2%. In contrast, survival of ACC protoplasts following recovery from LN(2) was 34 +/- 10% when the protoplasts were loaded in a 2.0 molar EG solution and unloaded in an isotonic sorbitol solution (1.03 osm). If ACC protoplasts were unloaded in an hypertonic sorbitol solution (1.5 osm), survival was 51 +/- 9%. These results indicate that the osmotic excursions incurred during the procedure are a major factor affecting survival.

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PubMed1990

Effect of preincubation temperature on in vitro light saturated photosystem I activity in thylakoids isolated from cold hardened and nonhardened rye.

Thylakoids isolated from winter rye (Secale cereale L. cv Muskateer) grown at 5 degrees C or 20 degrees C were compared with respect to their capacity to exhibit an increase in light saturated rates of photosystem I (PSI) electron transport (ascorbate/dichlorophenolindophenol --> methylviologen) after dark preincubation at temperatures between 0 and 60 degrees C. Thylakoids isolated in the presence or absence of Na(+)/Mg(2+) from 20 degrees C grown rye exhibited transient, 40 to 60% increases in light saturated rates of PSI activity at all preincubation temperatures between 5 and 60 degrees C. This increase in PSI activity appeared to occur independently of the electron donor employed. The capacity to exhibit this in vitro induced increase in PSI activity was examined during biogenesis of rye thylakoids under intermittent light conditions at 20 degrees C. Only after exposure to 48 cycles (1 cycle = 118 minutes dark + 2 min light) of intermittent light did rye thylakoids exhibit an increase in light saturated rates of PSI activity even though PSI activity could be detected after 24 cycles. In contrast to thylakoids from 20 degrees C grown rye, thylakoids isolated from 5 degrees C grown rye in the presence of Na(+)/Mg(2+) exhibited no increase in light saturated PSI activity after preincubation at any temperature between 0 and 60 degrees C. This was not due to damage to PSI electron transport in thylakoids isolated from 5 degrees C grown plants since light saturated PSI activity was 60% higher in 5 degrees C thylakoids than 20 degrees C thylakoids prior to in vitro dark preincubation. However, a two-fold increase in light saturated PSI activity of 5 degrees C thylakoids could be observed after dark preincubation only when 5 degrees C thylakoids were initially isolated in the absence of Na(+)/Mg(2+). We suggest that 5 degrees C rye thylakoids, isolated in the presence of these cations, exhibit light saturated PSI electron transport which may be closer to the maximum rate attainable in vitro than 20 degrees C thylakoids and hence cannot be increased further by dark preincubation.

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PubMed1990

Tubulin Isotypes in Rye Roots Are Altered during Cold Acclimation.

The cold stability of cortical microtubules in root-tip cells of winter rye (Secale cereale L. cv Puma) is altered by growth temperature (GP Kerr, JV Carter [1990] Plant Physiol 93:77-82). One hypothesis for the basis of this alteration is that different tubulin isotypes are present at different growth temperatures, and that the cold stability of microtubules is affected by these isotypic differences. We have explored the first part of this hypothesis by comparing protein extracts from roots of seedlings grown for 2 days at 22 degrees C (nonacclimated) or for an additional 2 or 4 days at 4 degrees C (cold-acclimated). Immunoblots of two-dimensional polyacrylamide gels were probed with monoclonal antibodies to alpha- and beta-tubulin. At least six alpha- and seven beta-tubulins were present in the extracts from both the nonacclimated and cold-acclimated roots. Changes in electrophoretic mobility and isotype number of both alpha- and beta-tubulin were observed after only 2 days at 4 degrees C. Further changes in tubulin were observed after 4 days at 4 degrees C. Changes in alpha-tubulin were more pronounced than those in beta-tubulin.

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PubMed1990

Effect of growth temperature and temperature shifts on spinach leaf morphology and photosynthesis.

The growth kinetics of spinach plants (Spinacia oleracea L. cv Savoy) grown at 5 degrees C or 16 degrees C were determined to allow us to compare leaf tissues of the same developmental stage rather than chronological age. The second leaf pairs reached full expansion at a plant age of 32 and 92 days for the 16 degrees C and 5 degrees C plants, respectively. Growth at 5 degrees C resulted in an increased leaf area, dry weight, dry weight per area, and leaf thickness. Despite these changes, pigment content and composition, room temperature in vivo fluorescence, and apparent quantum yield and light-saturated rates of CO(2) exchange or O(2) evolution were not affected by the growth temperature. Furthermore, 5 degrees C expanded leaves were found to be more resistant to photoinhibition at 5 degrees C than were 16 degrees C expanded leaves. Thus, it is concluded that spinach grown at low temperature is not stressed. However, shifting spinach leaves from 5 degrees C to 16 degrees C or from 16 degrees C to 5 degrees C for 12 days after full leaf expansion had occurred resulted in a 20 to 25% reduction in apparent quantum yields and 50 to 60% reduction in light saturated rates of both CO(2) exchange and O(2) evolution. This was not accompanied by a change in the pigment content or composition or in the room temperature in vivo fluorescence. It appears that leaf aging during the temperature shift period can account for the reduction in photosynthesis. Comparison of cold-hardened and non-hardened winter rye (Secale cereale L. cv Muskateer) with spinach by in vivo fluorescence indicated that rye is more sensitive to both short term and longer duration temperature shifts than is spinach. Thus, susceptibility to an abrupt temperature shift appears to be species dependent.

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