bluuebunny/crossref_metadata_2025 huggingface dataset:
Induction of chilling tolerance in cucumber (Cucumis sativus) seedlings by endogenous and applied ethanol
Authors: Frenkel Chaim , Erez Amoral
Published: May 2006

Five‐day‐old etiolated cucumber (Cucumis sativus L.) seedlings cv. Marketmore held at 2°C for 72 h developed chilling injury, resulting in desiccation and collapse of the hypocotyl tissue and eventual plant death. Hypoxia‐induced accumulation of ethanol and acetaldehyde led to tolerance of subsequent chilling, as evidenced by continued hypocotyl growth and freedom from injury. Attenuated accumulation of volatiles by applied bisulfite reduced the development of hypoxia‐induced chilling tolerance in seedlings. In seedlings held in normoxia cold tolerance was induced by applied ethanol vapors, whereas acetaldehyde had a marginal effect, suggesting that hypoxia‐induced cold tolerance may arise from the accumulation and activity of ethanol. Cold tolerance was also induced by exposure of seedlings to volatile anesthetics including n‐propanol, n‐butanol, chloroform and halothane, suggesting that ethanol activity may result from fluidization of membrane lipids. This view is consistent with results which showed that ethanol activity was not associated with lipid metabolism. However, development of cold tolerance in ethanol‐enriched tissues was time dependent, indicating that ethanol activity probably also entails biosynthetic event(s).
Photosynthetic response of P‐deficient Gracilaria tenuistipitata under two different phosphate treatments
Authors: García‐Sánchez María J. , Fernández José A. , Niell F. Xavier
Published: May 2006

Phosphorus‐deficient Gracilaria tenuistipitata Zhang et Xia was cultured for 15 days at two different inorganic phosphate (Pi) concentrations: 3 μM (low Pi treatmenl) or 30 μM phosphate (high Pi treatment). The amount of ribulose‐l,5‐bisphosphate carboxy‐lase/oxygenase (Rubisco), phycobiliproteins, Chl a and total soluble proteins were higher in the high Pi than in the low Pi treatment. The total N content of the low Pi plants was lower than in plants grown at high Pi concentrations whereas the amount of total C was highest in low Pi plants. The increase of Rubisco content in the high Pi treatment (3‐fold) was parallel to the enhancement of the maximum photosynthetic rate which increased 5‐fold. This correspondence was also found in the low Pi treatment in which Rubisco content and maximum photosynthesis did not change significantly from the initial values. The photosynthetic efficiency was also higher at high than at low Pi. The high Pi plants also showed higher dark respiration and growth rates. The data presented here suggest that marine macroalgae submitted to Pi deficiency exhibit a decrease in growth caused not only by Pi implication on energy transfer in photosynthesis and respiration, but also by the diminution of the amount of photosynthetic pigments and Rubisco.
Phosphofructokinase from the host fraction of chickpea nodules
Authors: Lee Hoi‐Seon , Copeland Les
Published: May 2006

Two phosphofructokinases (EC 2.7.1.11; PFK) have been isolated from the host fraction of nitrogen–fixing chickpea (Cicer arietinum L.) root nodules that were formed with Rhizobium sp. (Cicer) CC1192. The predominant enzyme, which is suggested to be cytosolic, was isolated as a large aggregate of molecular mass near 2 000 kDa and was purified to a high degree. The less abundant enzyme, suggested to be of plastid origin, had a native molecular mass of 186 kDa. Both forms of PFK displayed typical hyperbolic kinetics with MgATP and fructose‐6‐phosphate. The major form of PFK was strongly inhibited by phosphoenolpyruvate, 2‐phosphoglycerate and 3‐phos‐phoglycerate, and to a lesser extent by ADP, pyrophosphate, glucose‐6‐phosphate and 6‐phosphogluconate. KCl and phosphate were activators and relieved the effect of inhibitors. The major PFK was disaggregated in the presence of ATP into a species which had a molecular mass of approximately 550 kDa and a lower affinity for fructose‐6‐phosphate.
Anaerobic promotion of stem extension in Potamogeton pectinatus. Roles for carbon dioxide, acidification and hormones
Authors: Summers Jacky E. , Jackson Michael B.
Published: May 2006

Dark‐grown shoots of tubers of the aquatic monocot Potamogön pectinatus L. elongated more strongly in anaerobic than aerobic solutions over 5 days. The response was located in the stem rather than the leaf. Anaerobic carbon dioxide (CO2) production was similar to that in aerobic conditions. Approximately half the anaerobic stem extension was attributed to acidification of the submerging medium by respiratory CO2. Sparging with an anaerobic gas mixture of nitrogen and hydrogen to remove dissolved CO2 inhibited stem elongation and prevented acidification of the medium. Similarly, supplying CO2 anaerobically promoted stem elongation while acidifying the medium. Carbon dioxide was also active on aerobic shoots. The effect of CO2 on anaerobic stem extension could be mimicked with an acidic buffer. Anaerobic stem extension was inhibited by exogenous abscisic acid (ABA), while gibberellic acid and the gibberellin‐biosynthesis inhibitor paclobutrazol proved inactive. Exogenous indole‐3‐acetic acid promoted stem extension in the absence of oxygen. A strong gravitropic response by anaerobic stems of P. pectinatus was inhibited by the auxin‐efflux inhibitor naphthylphthalamic acid.
Drought‐ and ABA‐induced changes in photosynthesis of barley plants
Authors: Popova Losanka P. , Tsonev Tsonko D. , Lazova Galia N. , Stoinova Zhivka G.
Published: May 2006

The changes caused by drought stress and abscisic acid (ABA) on photosynthesis of barley plants (Hordeum vulgare. L. cv. Alfa) have been studied. Drought stress was induced by allowing the leaves to lose 12% of their fresh weight. Cycloheximide (CHI), an inhibitor of stress‐induced ABA accumulation, was used to distinguish alterations in photosynthetic reactions that are induced after drought stress in response to elevated ABA levels from those that are caused directly by altered water relations. Four hoars after imposition of drought stress or 2 h after application of ABA, Ihe bulk of the leaf's ABA content measured by enzyme‐amplified ELISA, increased 14‐ and 16‐fold, respectively. CHI fully blocked the stress‐induced ABA accumulation. Gas exchange measurements and analysis of enzyme activities were used to study the reactions of photosynthesis to drought stress and ABA. Leaf dehydration or ABA treatment led to a noticeable decrease in both the initial slope of the curves representing net photosynthetic rate versus intercellular CO2 concentration and the maximal rate of photosynthesis; dehydration of CHI‐treated plants showed much slower inhibition of the latter. The calculated values of the intercellular CO2 concentration, CO2 compensation point and maximal carboxylating efficiency of ribulose 1,5‐bisphosphate (RuBP) carboxylase support the suggestion that biochemical factors are involved in the response of photosynthesis to ABA and drought stress. RuBP carboxylase activity was almost unaffected in ABA‐ and CHI‐treated, non‐stressed plants. A drop in enzyme activity was observed after leaf dehydration of the control and ABA‐treated plants. When barley plants were supplied with ABA, the activity of carbonic anhydrase (CA, EC 4.2.2.1) increased more than 2‐fold. Subsequent dehydration caused an over 1.5‐fold increase in CA activity of the control plants and a more than 2.5‐fold increase in ABA‐treated plants. Dehydration of CHI‐treated plants caused no change in enzyme activity. It is suggested that increased activity of CA is a photosynthetic response to elevated ABA concentration.
Factors affecting transient gene expression in cultured radiata pine cotyledons following particle bombardment
Authors: Rey Manuel , González María Victoria , Ordás Ricardo J. , Tavazza Raffaela , Ancora Giorgio
Published: May 2006

Transfer and expression of the β–glucuronidase gene (gusA) in cultured cotyledons of radiata pine (Pinus radiata D. Don) were obtained by particle bombardment. Conditions for optimum transient expression were established by using plasmid pB[/12], delivered by gold particles, 1.6 μm in diameter, into 8‐day‐old cultured cotyledons. Helium pressure of 7.6 MPa, bombardment distance between the stopping screen and the target tissues of 6 cm, and 0.8 μg of plasmid DNA per bombardment proved to be the best parameters for transient expression; using these parameters 79% of bombarded cotyledons showed GUS activity, with 4.3 blue spots per cotyledon. This system was used for studying the expression of several gus‐driven promoters the expression of the sunflower ubiquitin gene promoter was higher (99% of positive cotyledons, with 14.2 blue spots per cotyledon) than that of the CaMV 35S promoter, whereas the rice actin and the maize alcohol dehydrogenase gene promoters gave lower gusA expression, as determined histochemically. These results were confirmed by using the gus fluorometric assay. Use of the sunflower ubiquitin gene promoter resulted in gusA expression up to 20 days after bombardment, with a significant level of gus expressing loci per bombarded cotyledon, whereas with the CaMV 35S promoter gusA expression was lost 12 days after bombardment.
The gigas mutant in pea is deficient in the floral stimulus
Authors: Beveridge Christine A. , Murfet Ian C.
Published: May 2006

Identification of a gene acting in the floral stimulus pathway should provide a basis for determining the identity of this elusive substance. Our tests indicate the Gi (gigas) gene in pea (Pisum sativum L.) acts in this manner. The gigas mutant was selected by Dl M. Vassiteva following gamma radiation of the late flowering, quantitative long day cultivar Virtus. The gigas trait showed single gene recessive inheritance and the mutant allele was symbolised gi consistent with our preliminary report. Gigas plants were later flowering than the initial line in all conditions tested and they showed an enhanced response to photoperiod and vernalisation. Unvernalised gigas plants did not flower under a 24‐h photoperiod comprising 8 h of daylight and 16 h of weak (3μmol m−2 s−1) incandescent light and they took on a phenotype similar to the vegl (vegetative) mutant in pea. However, genetic tests showed the two mutants were not allelic. Three or four weeks vernalisation at 4−C resulted in 100% flowering of gigas plants under the 24‐h photoperiod. Applied gibberellin A3 inhibited flowering in gigas plants given partial cold induction. Grafting studies showed the promotive effect of vernalisation occurred in the shoot. Grafting studies were also used to examine the physiological basis of delayed flowering in the gigas mutant. These studies indicated that gigas plants produced normal levels of flower inhibitor and they responded in a normal manner to the floral stimulus, Reciprocal grafts were made between the gigas mutant and the wild‐type initial line. Under the 24‐h photoperiod, either a wild‐type root‐stock with cotyledons or a wild‐type shoot induced flowering in a gigas graft partner. However, under a 9‐h photoperiod, flowering was only induced if the wild‐type partner possessed both roots and a shoot. We conclude that gigas plants are deficient in the floral stimulus or a precursor which can be supplied across a graft union by a wild‐type donor. Of the 12 major flowering genes known in pea, Gi is the first found to act on the synthesis pathway for the floral stimulus.
Nuclear and cytoplasmic “stay‐green” mutations of soybean alter the loss of leaf soluble proteins during senescence
Authors: Guiamet Juan J. , Giannibelli M. Cristina
Published: May 2006

In soybean (Glycine max [L.] Merr.) the homozygous combination of the recessive alleles dI and d2 (i.e., dldld2d2) at two different nuclear loci or the cytoplasmic gene cytG inhibit chlorophyll degradation during senescence; i.e. their leaves are green when they are shed. The main objectives of the present work were: (J) to determine whether these “stay‐green” genes also interfere with the loss of the bulk of leaf soluble proteins and ribulose bisphospnate carboxylase/oxygensase (Rubisco; EC 4.1.1.39) during senescence and (2) to relate this to alterations in leaf proteolytic activity. Leaves of the normal. Yellowing cvs Clark and Harosoy lost about 90% of their soluble proteins before abscission. The abscising leaves of these cultivars contained no detectable Rubisco. By contrast, protein degradation was significantly less in leaves of near‐isogenic lines of Clark and Harosoy carrying dIdId2d2, with or without G (a dominant nuclear gene in a third locus causing green seed coats). These leaves still retained 50% of the soluble protein and large amounts of both subunits of Rubisco at the time of abscission. Alone, neither dl nor d2 had any effect. The cytoplasmic gene cytG slowed the loss of Rubisco. although eventually when leaves were shed they contained as little Rubisco as Clark. Despite inhibition (i.e. dIdId2d2 and GGdIdId2d2) or retardation (i.e. cytG) of protein loss, these mutant genotypes did not differ from Clark in the breakdown of endogenous Rubisco by leaf extracts (“autodigestion”). The wild‐type alleles in the dI and d2 loci may control a central regulatory process of the senescence syndrome.
Protein deamidases from germinating seeds
Authors: Vaintraub Iosif , Kotova Ludmila , Shaha Ranajid
Published: May 2006

Enzymes catalyzing the deamidation of seed storage proteins were found in germinating seeds of kidney beans (Phaseolus vulgaris L. cv. Moldavian) and squash (Cucurbita pepo L. cv. Mozoleevskaya). They were partially purified and characterized. The properties of these enzymes closely resemble those of the protein deamidase in germinating wheat grains. The detection of similar protein deamidases in germinating seeds of plants belonging to phytogenetically unrelated species indicates that protein deamidases are of considerable physiological significance.
Rhythmic growth and carbon allocation in Quercus robur. Sucrose metabolizing enzymes in leaves
Authors: Alaoui‐Sossé B. , Ricaud S. , Barnola P. , Dizengremel P.
Published: May 2006

The high sucrose phosphate synthase (SPS) capacity and the low soluble acid invertase activity of mature leaves of the first flush of leaves remained stable during second flush development. Conversely, fluctuations of sucrose synthase (SS) activity were in parallel with the sucrose requirement of the second flush. Sucrose synthase activity (synthesis direction) in first flush leaves could increase in ‘response’ to sink demand constituted by the second flush growth. Only the ptotosynthates provided by flush mature leaves were translocated for a current flush, while the starch content of these leaves remained stable. After their emergence, second flush leaves showed an increase in SPS and SS (Synthetic direction) activities. The high sucrose synthesis in second flush leaves was used for leaf expansion. When young leaves were 30% fully expanded (stage II20), SPS activity showed little change whereas SS activity declined rapidly toward and after full leaf expansion. The starch accumulation in the young leaves occured simultaneously with their expansion. Developing leaves showed a high level of acid invertase activity until maximum leaf expansion (stage II1). In first and second flush leaves, changes in acid invertase activity correlated positively with changes in reducing sugar concentrations. Alkaline invertase and sucrose synthase (cleavage direction) activities showed similar changes with low values when compared with those of acid invertase activity, especially in second flush leaves. The present results suggest that soluble acid invertase was the primary enzyme responsible for sucrose catabolism in the expanding common oak leaf.
Organization of the reduced plastid genome of Lathraea clandestina, an ahlorophyllous parasitic plant
Authors: Delavault Philippe M. , Russo Nathalie M. , Lusson Nathalie A. , Thalouarn Patrick A.
Published: May 2006

Heterologous probes representing the entire tobacco chloroplast genome were used to investigate the degree of sequence conservation in the plastid DNA of the totally achlorophyllous plant Lathraea clandestina. Lathraea, a root parasite that grows in the soil, has retained a plastid genome in which the inverted repeat region (IR) is well conserved, with the exception of a short deletion in one of its extremities close to the large single copy region (LSC). Transcription of the 16S rRNA gene located in the IR was demonstrated, suggesting the functionality of the gene expression apparatus. Besides genes for ribosomal proteins (rps7 and rpl20) and for the plastid‐encoded subunits of RNA polymerase (rpoA, rpoB, rpoC1 and rpoC2) were amplified by PCR. The single copy regions which contain most of the bioenergetic genes are more divergent than the inverted repeat regions with deleted or strongly altered sequences. This is particularly noticeable in the small one (SSC) which contains, in land plants studied so far, ndh genes for subunits of an NAD(P)H dehydrogenase. Despite some large deletions in the LSC, PCR experiments have shown that some photosynthetis genes, either functional (rbcL) or not (atpB–E) have been maintained. In addition heterologous hybridizations demonstrate that some genes (psaA, psaB, psbC–D) not amplified by PCR have been retained, at least partially. Because the psbA gene, despite having been amplified by PCR, did not map to any location on the Lathraea plastid genome, it is suspected that this sequence has been incorporated in another genome. From these findings we conclude that Lathraea plastid DNA is altered to a lesser extent than in Epifagus, a member of the Orobanchaceae, whilst being very different from Cuscuta reflexa whose plastid DNA (ptDNA) still contains all the photosynthetic genes found in autotrophic angiosperms. The maintenance of an intact rbcL gene might be the reason (or one of the reasons) why Lathraea has retained a plastid genome, even if the function of Rubisco in its amyloplasts remains unclear.
Aluminum‐induced alterations in lipid composition of microsomal membranes from an aluminum‐resistant and an aluminum‐sensitive cultivar of Triticum aestivum
Authors: Zhang Guichang , Slaski Jan J. , Archambault Daniel J. , Taylor Gregory J.
Published: May 2006

We have studied the effect of aluminum (Al) on the lipid composition of microsomal membranes isolated from 5‐mm root tips of an Al‐resistant (T 741) and an Al‐sensitive (Katepwa) cultivar of Triticum aestivum L. Exposure of both genotypes to 10 and 50 μM AeCl3 for 1 day had no effect on lipid composition; however, decreases in phospholipids and increases in monogalactosyl diacylglycerols, free sterols, free fatty acids and triacylglycerols were observed with prolonged exposure (3 days) to 5O μM AlCe3. Several genotype‐specific changes were also observed under these conditions. The content of digalactosyl diacylglycerols increased by 66.7% in Katepwa. but decreased slightly in PT 741. Thus, the ratio of rnonogalactosyl diacylglycerols to digalactosyl diacylglycerols increased by 46.2% in PT 741, but decreased by 21.3% in Katepwa. Genotype‐specific differences were also observed in steryl lipids. Treatment with Al induced a 70.2% increase in sterylglucosides and a 23.3% increase in acylated sterylglucosides in Katepwa. In contrast, a 18.9% decrease in acylated sterylglucosides and no changes in sterylglucosides were observed in PT 741. Our limited understanding of the effect of membrane composition on membrane structure and function makes it difficult to predict how these changes relate to Al toxicity and resistance. While it is possible that many changes reflect the toxic effects of Al, we believe that changes observed only in the Al‐resistant genotype could contribute to continuous growth in the face of Al stress.
Inositol 1,4,5‐trisphosphate formation in leaves of winter oilseed rape plants in response to freezing, tissue water potential aed abscisic acid
Authors: Smolénska‐Sym Gabriela , Kacperska Alina
Published: May 2006

Time courses of formation of inositol 1,4,5‐trisphosphate (IP3) were followed in the leaves of non‐acclimated and cold (2°C)‐acclimated winter oilseed rape (Brassica napus L. var. oleifera) plants, subjected to different freezing temperatures or to polyethylene glycol 8000 (PEG) and abscisic acid (ABA) treatments. Changes in water potential (Ψw) and in ABA level in the frost‐ and PEG‐treated tissues were also determined. Results obtained indicate that temperatures sligthly higher than LT50 induced a transient and substantial increase in IP3 level, both in non‐acclimated and cold‐acclimated tissues. At comparable freezing temperature (–5°C) the response of cold‐acclimated leaves was lower than that of non‐acclimated ones. The PEG‐depedent decrease in Ψw to –0.9 MPa or ABA (0.1 mM) treatment gave rise to a transient increase in IP3 content in non‐acclimated tissues only. Collectively, the data indicate that cold acclimation of plants may lead to lower cell responsiveness to the factors studied in terms of induction of IP3 formation. Changes in the IP3 content, observed in the present experiments, support our previous suggestion that non‐killing freezing temperatures may induce the phosphoinositide pathway, both in non‐acclimated and cold‐acclimated tissues. Lowering of tissue water potential to some threshold value or a high exogenous ABA supply may mimic the freezing‐dependent reaction in the non‐acclimated leaves.
Differences in transcription products and in translation and enzymatic activities during the early stages of imbibition of Phacelia tanacetifolia seeds with germination inhibited by light
Authors: Pirovano Livia , Morgutti Silvia , Espen Luca , Cocucci Sergio M.
Published: May 2006

To elucidate the inhibitory effect of light on the germination of the negatively photo‐blastic seeds of Phacelia tanacetifolia Benth. (cv. Bleu Clair). we have compared the changes that occur during the first 24 h of imbibition in the dark and in the light. Here, we give data on transcription products, translation activity, activities of some enzymes involved in the metabolic reactivation of seeds (glucose‐6‐phosphate dehydrogenase, pyruvate kinase, glucokinase and malate dehydrogenase), and the capability to absorb L‐[U‐14C]‐leucine. During the first stages of imbibition, the changes in the protein pattern and in the mRNA populations that occurred were not related to the light/dark regimes. Differences due to the light treatment did not appear until after 24 h. when new microsomal proteins appeared in the dark and some mRNA populations encoding low molecular mass polypeptides were increased in the light. The translation activity, measured as L‐[U‐14C]‐leucine incorporated into proteins and as the ratio polysomes/monosomes, increased with time in both darkness and light, but to a much higher extent in the dark. The activities of the four enzymes tested were higher in the light than in the dark before 16 h, then decreased in the light and increased sharply in the dark. Together with the behaviour of the increase in the ratio polysomes/monosomes in the dark, this suggests an increased rate of protein degradation in the dark during the period 0–16 h. The absorption of L‐[U‐14C]‐leucine was severely inhibited by light during the whole period studied, as expected since light inhibits the reactivation of the transport mechanisms at the plasma membrane. In seeds imbibed in the dark and then transferred to light, the inhibition by light of absorption and of incorporation into proteins of L‐[U‐14C]‐leucine, as well as the inhibition of the increase in the ratio poly‐somes/monosornes, was effective before the 22nd h; after which time the control exerted by light disappeared.
Effect of sulphate on photosynthesis in greenhouse–grown tomato plants
Authors: Xu H. L. , Lopez J. , Rachii F. , Tremblay N. , Gauthier L. , Desjardins Y. , Gosselin A.
Published: May 2006

Sulphate accumulates in the rhizosphere of plants grown in hydroponic systems. To avoid such sulphate accumulation and promote the use of environmentally sound hydroponic systems, we examined the effects of four sulphate concentrations (0.1, 5,2, 10.4 and 20.8 mM) on photosynthesis, ribulose‐l,5‐bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) activities and related physiological processes in greenhouse–grown tomato plants (Lycopersicon esculentum Mill. cv. Trust). The lowest sulphate concentration (0.1 mM) significantly decreased photosynthetic capacity (Pc) and Rubisco activities on a leaf area basis. This result was supported by our data for dry matter per plant, which was low for plants in the 0.1 mM treatment. The photosynthesis‐related variables such as leaf conductance, chlorophyll and soluble protein were lowest for the 0.1 mM treatment. Both total Rubisco activity and the activated ratio were reduced with this treatment. However, Rubisco activities expressed per g of protein or per g of chlorophyll were not significantly affected. These results suggest that sulphur deficiency depressed Pc– by reducing the amount of both Rubisco and chlorophyll and by causing an inactivation of Rubisco. The ratio of organic sulphur vs organic nitrogen (S/N) in plants of the 0.1 mM treatment was far below the normal values. This low S/N ratio might be accountable for the negative effect of low sulphate on Pc and plant growth. Pc and dry matter were not affected until sulphate concentration in the nutrient solution reached a high level of 20.8 mM.
The complex circadian system of Gonyaulax polyedra
Authors: Roenneberg Till
Published: May 2006

Circadian oscillations are a fundamental biological property from bacteria to humans. The molecular mechanisms which produce a ca 24‐h rhythmicity are still unknown but it has become clear that they are part of the biochemical machinery of the single cell. The cellular circadian system can be favorably studied in single‐cell organisms such as the dinoflagellate Gonyaulax polyedra. The complexity of this circadian model system, which consists of at least two circadian oscillators, receives light via two input systems with different spectral sensitivities, and has several feed–back loops between the central oscillator(s) and the environment, is described here.
Dynamics of the response of cyanobacteria to salt stress: Deciphering the molecular events
Authors: Joset Francoise , Jeanjean Robert , Hagemann Martin
Published: May 2006

Cyanobacteria, the only prokaryotes performing oxygemc photosynthesis and probable ancestors of chloroplasts, constitute valuable models for the study of the molecular mechanisms involved in tolerance to high salinity, or to its corollary, drought, a major agricultural problem. The critical demands of cyanobacteria exposed to high salinity, i.e., accumulation of osmoprotectors and extrusion of sodium ions, are met through immediate activation and/or long term (protein synthesis‐dependent) adaptation of various processes: (1) uptake and endogenous biosynthesis of osmotica, the nature and amount of which are strain‐ and salt concentration‐dependent; (2) enhancement of P‐ATPase activity and active extrusion of sodium ions; (3) probable modifications of membrane lipid composition: and (4) increased energetic capacity, at the level of cyclic electron flow around photosystem I (through routes induced under these conditions) and cytochrome c oxidase. The processes involved highlight similarities with general stress responses and with salt stress responses in plants. Deciphering the molecular and genetic events regulating these coordinated responses is presently starting in cyanobacteria.
Two barley catalase genes respond differentially to light
Authors: Acevedo Alberto , Skadsen Ronald W. , Scandalios John G.
Published: May 2006

Cloned catalase probes from barley (Hordeum vulgare L.) and maize (Zea mays L.) were used to examine catalase gene expression in greened and etiolated leaves of several barley lines. Etiolated leaves had greater levels of an mRNA detected by barley Cat1, compared with greened leaves, in all lines. In contrast, a Cat2‐like mRNA (homologous to Cat2 of maize) was induced by light and accumulated to high levels in greened leaves, compared to the negligible levels detected in etiolated leaves. This suggests that barley contains light‐inducible and light‐repressible catalase genes. In the catalase‐deficient barley mutant RPr 79/4, no hybridization signal was detected when RNA from greened or etiolated leaves was probed with maize Cat2, indicating that this mutant is deficient for the light‐induced Cat mRNA. In etiolated seedlings of both RPr 79/4 and its motherline, the level of the Cat1 mRNA increased coordinately with a steady increase in catalase activity. Even though the mutant RPr 79/4 was able to grow to maturity in normal air, it sustained chlorosis and significant head sterility, probably due to the lack of a light‐inducible catalase. Although the mutant RPr 79/4 is not completely lacking catalase (EC 1.11.1.6), the loss of the CAT‐1 isozyme is evidently harmful. This observation underscores the protective role of catalases in plants.
Loss of chlorophylls, cessation of photosynthetic CO2 assimilation and respiration in the poikilochlorophyllous plant Xerophyta scabrida during desiccation
Authors: Tuba Z. , Lichtenthaler H. K. , Csintalan Zs. , Nagy Z. , Szente K.
Published: May 2006

During a slow desiccation in photosynthetically fully active leaves of the poikilochlorophyllous desiccation‐tolerant (PDT) monocotyledon Xerophyta scabrida (Pax) Th. Dur. et Schinz (Velloziaceae), thylakoid activity, CO2 assimilation and respiration decline and chlorophylls and carotenoids are successively broken down. The initially slow rate of leaf water loss is related to the large reduction in leaf area which is reflected in the decrease of specific leaf area. Chlorophylls are broken down faster than carotenoids. The ratio of the variable chlorophyll fluorescence, an indicator of photosynthetic activity (Rfd690‐values), shows that the functionality of thylakoids and chlorophylls is successively lost during desiccation. The decline in net CO2 assimilation in desiccating leaves is largely caused by stomatal closure. The complete cessation of CO2 assimilation, however, is due to the breakdown of chlorophylls and thylakoids. Respiration continued during desiccation and remained active far below ‐3.2 MPa leaf water potential. The differences during desiccation of the photosynthetic apparatus between poikilochlorophyllous and homoiochlorophyllous desiccation‐tolerant plants are discussed.
Inheritance of stomatal conductance in cotton (Gossypium barbadense)
Authors: Percy Richard G. , Lu Zhenmin , Radin John W. , Turcotte Edgar L. , Zeiger Eduardo
Published: May 2006

Stomatal conductance in improved Pima cotton cultivars (Gossypium barbadense) has been previously shown to be positively associated with heat resistance and yield potential. In the present study we determined the mode of inheritance of stomatal conductance in crosses of six G. barbadense parents varying in origin, degree of agronomic development and stomatal conductance. Parents included a primitive tropical cotton (B368), two obsolete cultivars (St Vincent V135, Pima 32), one modern commercial line (Pima S‐6) and two elite genotypes of the Pima germplasm (P70, P73). These lines showed distinct differences in stomatal conductance, under greenhouse and field conditions. The primitive B368 had the lowest conductance, and the elite lines the highest. Generation means analysis was used to quantify genetic effects in the crosses P70 × St Vincent V135, Pima S‐6 × B368, Pima S‐6 × Pima 32, P73 × Pima 32 and P73 × Pima S‐6. Best‐fit models of the inheritance of stomatal conductance varied in complexity from a simple additive‐dominance model in the cross P70 × St. Vincent V135 to models displaying digenic epistatic interactions in the remaining crosses. Significant additive mean effects for stomatal conductance were detected in all crosses. Dominance mean effects were significant in the crosses P73 × Pima 32 and P73 × Pima S‐6. Broadsense heritability estimates of stomatal conductance were relatively low (0.16–0.44) in all crosses except Pima S‐6 × B368 (0.74). Results also show that the mode of inheritance of stomatal conductance is multigenic, and may have maternal as well as nuclear components. Recouping higher stomatal conductance levels from genetically wider crosses appears feasible and could proceed at a moderate rate. Fixing higher levels of stomatal conductance in populations from crosses of elite germplasm may be more difficult because of the presence of dominant mean effects and digenic epistatic interactions.
Correlation between the inhibition of photosynthesis and the decrease in area of detached leaf discs or volume/absorbance of protoplasts under osmotic stress in pea (Pisum sativum)
Authors: Saradadevi K. , Padmasree K. , Raghavendra A. S.
Published: May 2006

Exposure to osmotic stress reduces leaf area and protoplast volume while decreasing photosynthesis. But the measurement of protoplast volume is tedious, while rapid determinations of leaf area in the field are difficult. We evaluated the quantitative relationship between the extent of decrease in area of detached leaf discs or the volume of protoplast of pea (Pisum sativum) and reduction in their photosynthetic capacity under osmotic stress. Osmotic stress was induced by increasing sorbitol concentration in the surrounding medium of the leaf discs from zero to 1.0 M (‐3.1 MPa), and in case of protoplasts from 0.4 M (‐1.3 MPa, isotonicity) to 1.0 M (‐3.1 MPa, hypertonicity). There was a high degree of positive correlation between the extent of reduction in the area of detached leaf discs or the volume of protoplasts (indicated by diameter or absorption at 440 nm) and the decrease in photosynthesis. The correlation coefficients between inhibition of photosynthesis and the decrease in leaf disc area or protoplast volume were 0.96 and 0.99, respectively. We therefore suggest that the decrease in absorbance at 440 nm (corrected for turbidity at 750 nm) can be used as a simple measure to predict the inhibition due to osmotic stress of photosynthesis in mesophyll protoplasts. Similarly, the reduction in area of detached leaf discs could also be a very simple and useful criterion to assess osmotic tolerance of photosynthesis.
Functional relationship between chlorophyll content and leaf reflectance, and light‐capturing efficiency of Japanese forest species
Authors: Lei Thomas T. , Tabuchi R. , Kitao M. , Koike T.
Published: May 2006

We examined the functional relationship between chlorophyll concentrations and light spectral absorption in 16 species of woody, vine and herbaceous plants in northern Japan. Leaves of each species from under forest shade and in more open sites were measured for chlorophyll, specific leaf area (SLA) and spectral absorption. In all species, SLA increased and the Chl a:b ratio declined in shade‐ vs open‐grown leaves indicating an adaptive adjustment to forest shade in these leaf characters. However, the expected increase in the ratio of 680 to 700 nm absorption in shade leaves did not occur in all species. Light absorption at 680 relative to 700 nm was lower in the shade leaves of Acer japonicum. Kalopanax pictus, Panax japonicus and Petasites japonicus even with a reduced Chl a:b, a commonly accepted indicator of shade adaptation. Therefore, spectral measurements in these species failed to support Chl concentrations that were expected to confer an improvement in the absorption of red light (<680nm) deficient relative to far‐red light (>700 nm) in the forest shade. Compared with other species, the absorption pattern of these four ‘non‐conforming’ species is associated with a higher ratio of shade:open leaves in reflectance spectra in the 600–750 nm range. This suggests an increased reflectance in shade leaves caused by changes in leaf surface properties which are not immediately apparent. We conclude that adaptive spectral absorption cannot always be inferred from changes in specific leaf area and chlorophyll a and b concentrations.
Water relations of GA‐ and ABA‐deficient tomato mutants during seed and fruit development and their influence on germination
Authors: Liu Yongqing , Bino Raoul J. , Karssen Cees M. , Hilhorst Henk W. M.
Published: May 2006

To explain the differing germination behaviour of seeds of wild type, gibberellin‐deficient (gibl) or abscisic acid‐deficient (sit”) mutants of tomato (Lycopersicon esculentum Mill. cv. Moneymaker), growth and water relations of fruit tissues, seeds and embryos were determined during development. The objective was to determine whether the hormones influenced water relations of fruit and seed tissues and as a consequence germinability. Despite the up to 70% lower fruit weight of the mutants, the fresh and dry seed weights were similar to that of the wild type. Water relations of pericarp and locular tissues in wild type and gibl fruits were characterized by a slowly increasing Ψa that reached a constant value Ψ of −0.60 MPa at 35–40 days after anthesis, resulting in a complete loss of turgor. However, sitw fruit tissues maintained their turgor throughout development, mainly as a result of considerably lower Ψ values but similar Ψ values compared with the other genotypes. The Ψ of wild type and gibl seeds decreased from ‐0.50 to ‐0.80 MPa and Ψ from ‐0.80 to ‐1.00 MPa between day 30 and 40. From day 40 onwards, Ψp was similar in both genotypes, approximately 0.20 MPa. As in the fruit tissues, sitw seed water relations were also characterized by higher turgor values than the other genotypes. Up to day 40, Ψp was ca 0.40 MPa, dropped temporarily to zero, and increased again to approximately 0.40 MPa at day 50. Embryo water relations of both mutants deviated from the wild type in that Ψp of the gibl and sitw embryos remained at 3.5 MPa and 2.5 MPa, respectively, from day 40 onward, whereas in wild type embryos Ψp decreased from 3.0 MPa at day 35 to approximately 1.0 MPa at 50 days after anthesis. This was mainly due to an increasing Ψn which was absent in the mutants. Throughout development there was equilibrium between Ψ of pericarp, locular tissues and seeds but between embryo and seed or fruit tissues Ψ gradients of up to 1.5 MPa were calculated in the wild type, and up to 1.0 MPa in the mutants. Thus, precocious germination is prevented by the action of the fruit's osmotic environment and ABA on the seed tissues surrounding the embryo and not the embryo itself. Embryos have a Ψ which is low enough to overcome the solute potential of the fruit tissues throughout development.
Functional organization of thylakoid membranes in viable pea mutants with low chlorophyll content
Authors: Krendeleva T. E. , Kukarskikh G. P. , Nizovskaya N. V. , Rubin A. B.
Published: May 2006

The functional organizations of thylakoid membranes from wild type pea (Pisum sativum L. cv. Kapital) and two viable mutants with low chlorophyll (Chl) contents were compared. Nuclear mutations in mutants 7 and 42 led to two‐ and three‐fold decrease in total chlorophyll content, respectively. In spite of low Chl content mutants showed 80% photosynthetic activity, biological productivity, and seed production. It has been shown that mutant membranes differed from that of wild type by Chl distribution between the pigment‐protein complexes and by stoichiometry of the main electrontransport complexes. The ratio photosystem I (PSI): photosystem II (PSII): cytochrome (Cyt) bjf complex: Chl was 1:1.1:1.2:650 in wild type chloroplasts, 1:1.8:1.7:600 in mutant 7, and 1:1.5:1.9:350 in mutant 42. PSI‐ and PSII‐dependent electron‐transport activities were enhanced in the mutants per mg Chl in proportion to number of reaction centers. The activity of the non‐cyclic electron‐transport chain increased in proportion to PSII and Cyt bjf complexes. The amount of ATP synthetase per unit of Chl as estimated by H−ATPase activity was much greater in mutant thylakoids, which is favorable for photosynthetic energy transduction. The low content of the light‐harvesting complexes (LHC) in mutants is compensated by an increase of the number of PSII and Cyt bjf complexes, which eliminates the bottleneck at the site of plastoquinone oxidation.
Use of clones increases the power of physiological experiments on coastal Douglas‐fir
Authors: Burr Karen E. , Tinus Richard W.
Published: May 2006

The statistical benefit of reduced variability in experiments with clones was quantified with cold hardy Douglas‐fir (Pseudotsuga menziesii var. menziesii [Mirb.] Franco) ramets from six clones from a single full‐sib family and a check group of open‐pollinated seedlings from a bulk seed collection from the same geographic seed source. All groups were cold deacclimated under controlled conditions. The variability in response for physiological attributes (cold hardiness, root growth potential, days to bud‐break) was compared within and among groups by using statistical power analyses. Sample sizes required to detect significant differences of varying magnitude between two hypothetical treatment means were calculated. Differences among clones in the average response exhibited for each physiological attribute were large, but within‐clone variability was low, relative to the check group of seedlings. Selection of plant material for a hypothetical experiment from this population of several identifiable clones would have consistently resulted in an experiment with greater power than an experiment using these ramets without the clone identities. From a statistical perspective, the best approach to reduce the number of replicates needed to detect treatment differences was selection of experimental plant material from a single clone, especially with prior screening for the most homogeneous clone for the physiological attributes and time periods of interest. However, from a biological perspective, use of a single clone should be approached with caution because of the lack of representation of natural population variability and the possible inability to broadly apply experimental results.
Hydrolysis of glucuronide‐based substrates mediated by tungsten, Cu2+, Fe2+, and Zn2+
Authors: Wozniak Chris A. , Owens Lowell D.
Published: May 2006

A variety of metal microprojectiles are currently used for carrying foreign DNA into living cells via particle‐acceleration techniques. While developing a microprojectile‐mediated protocol for transforming cells of sugarbeet (Beta vulgaris L.), formation of a blue precipitate was observed with the indigoqenic substrate 5‐bromo‐4‐chloro‐3‐indolyl‐β‐D‐glucuronic acid (X‐gluc) in the absence of gusA DNA encoding β‐D‐glucuronidase (GUS). Tungsten microcarriers, but not gold or silicon carbide, proved capable of catalyzing the cleavage of the glucuronide residue from three histochemical substrates evaluated: X‐gluc, salmon X‐gluc and magenta X‐gluc. Indigo‐stained sugarbeet cells were observed following bombardment with tungsten in the absence of DNA. Addition of oxidative catalysts to tungsten microcarriers during substrate incubation had no apparent effect on the metal‐mediated catalysis. Treatment of microcarriers with Proteinase K and heat ruled out the presence of enzymes. Microbiological evaluation indicated the absence of contaminating microbes. Similarly, metal‐catalyzed hydrolysis of the fluorogenic substrate 4‐methylumbelliferyl‐β‐D‐glucuronic acid (4‐MUG) was observed in the presence of tungsten spheres but not with gold or silicon carbide particles. With this substrate, hydrolysis also occurred with millimolar concentrations of Cu2+, Fe2+ and Zn2+ ions. Consequently, careful monitoring of DNA‐minus controls and avoidance of millimolar concentrations of Cu2+, Fe2+ and Zn2+ ions are recommended in microprojectile bombardment experiments where transient assays for gusA expression are performed.
Induction of leaf senescence in Arabidopsis thaliana by long days through a light‐dosage effect
Authors: Nooden Larry D. , Hillsberg Jennifer W. , Schneider Michael J.
Published: May 2006

Given the influence of photoperiod on reproductive development and whole‐plant senescence in monocarpic plants, one would suspect that leaf senescence in these plants might be under photoperiodic control. In Arabidopsis thaliana, which is monocarpic and also a nonobligate long‐day (LD) plant, LDs (16 h, 300 μmol m−2 s−1) caused leaves to die earlier than did short days (SDs, 10 h). Since leaf longevity was not paralleled by the reproductive development in the present study, the reproductive structures did not seem to be the primary controls of leaf senescence. The LD effect appeared to depend on the amount of light rather than on day length, for leaves given LDs at reduced light intensity (180 μmol m−2 s−1) lived longer than those in LDs with full light. In addition, the higher light intensity promoted chlorophyll loss and anthocyanin accumulation in LDs. Thus, senescence of these leaves seems to be governed by light dosage rather than photoperiod. Light may play a natural role in promoting the senescence of A. thaliana leaves.
Seasonal patterns of dehydrins and 70‐kDa heat‐shock proteins in bark tissues of eight species of woody plants
Authors: Wisniewski Michael , Close Timothy J. , Artlip Timothy , Arora Rajeev
Published: May 2006

Although considerable effort has been directed at identifying and understanding the function and regulation of stress‐induced proteins in herbaceous plants, reports concerning woody plants are limited. Studies with herbaceous crops have revealed similarities in the types of proteins that accumulate in response to a wide array of abiotic stresses and hormonal cues such as the accumulation of abscisic acid. Many of the identified proteins appear to be related to dehydrins (the D‐11 subgroup of late‐embryogenesis‐abundant proteins). The objective of the present study was to determine if seasonal induction of dehydrins is a common feature in woody plants and to see if seasonal patterns existed for other stress‐induced proteins. Bark tissues from eight species of woody plants were collected monthly for a period of 1.5 years. The species included: peach (Prunus persica) cv. Loring; apple (Malus domestica) cv. Golden Delicious; thornless blackberry (Rubus sp.) cv. Chester; hybrid poplar (Populus nigra); weeping willow (Salix babylonica); flowering dogwood (Cornus florida); sassafras (Sassafras albidum); and black locust (Robinia pseudo‐acacia). Immunoblots of bark proteins were probed with a polyclonal antibody recognizing a conserved region of dehydrin proteins, and monoclonal antibodies directed against members of the HS70 family of heat‐shock proteins. Some proteins, immunologically related to dehydrins, appeared to be constitutive; however, distinct seasonal patterns associated with winter acclimation were also observed in all species. The molecular masses of these proteins varied widely, although similarities were observed in related species (willow and poplar). Identification of proteins using the monoclonal antibodies (HSP70, HSC70, BiP) was more definitive because of their inherent specificity, but seasonal patterns were more variable among the eight species examined. This study represents only a precursory examination of several proteins reported to be stress related in herbaceous plants, but the results indicate that these proteins are also common to woody plants and that further research to characterize their regulation and function in relation to stress adaptation and the perennial life cycle of woody plants is warranted.