bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular aspects of heterosis in plants
Authors: Tsaftaris S. Athanasios 
Published: May 2006

Since Shull's original description of heterosis, breeders have made wide use of this phenomenon. However, while agronomists have been utilizing heterosis as a means of improving crop productivity, the biological basis of heterosis remains unkown. It is generally believed that our understanding of heterosis will enhance our ability to form new genotypes which may be used directly as F1 hybrids or form the basis for future selection programmes. While the original concept of heterosis resulted from studies at the phenotypic morpohological level, they were soon followed by biochemical data with the advent of electrophoresis and the consequent ease of accumulation of data related to isozyme variability. However, the large number of restriction fragment length polymorphisms from more recent studies has allowed the development of linkage maps with a high degree of resolution useful in locating and manipulating quantitative trait loci (QTL). When substantial numbers of such neutral markers were used to measure genetic distance in large numbers of maize inbreds, very significant correlations were recorded between parental genetic distance and hybrid performance. Through the same approach, a relatively small number of QTLs dispersed through the maize genome were identified which show clear overdominance expression controlling heterosis.The hypothesis was made that some QTLs could code for regulatory proteins since these proteins are able to control a vast array of other structural genes, the products of which are necessary for the expression of complicated characters such as yield and heterosis for yield. The few such proteins identified thus far are all multimeric proteins with the heteropolymers exhibiting significantly different activities in comparison with the homopolymers, that is in compliance with the clear overdominance manifestation of the few QTLs analyzed so far.In addition, parameters derived from the variability of genome expression assessed through studies of polymorphisms in the amounts of individual proteins or mRNAs show numerous significant correlations between these indices and hybrid vigor. These correlations supported the conclusion that QTLs could be loci controlling the amount of mRNAs or proteins synthesized from a number of structural genes, and stress the significance of both the regulatory proteins (and their encoding genes) and the structural genes, being regulated, in manifestation of complicated characters, such as heterosis.
Effects of UV‐B radiation and nitrogen starvation on enzyme activities in isolated plasma membranes of Euglena gracilis
Authors: Petersen‐Mahrt Silja K. , Ekelund Nils G. A. , Widell Susanne 
Published: May 2006

Circadian rhythms are characteristic of many physiological and biochemical processes in the freshwater flagellate Euglena gracilis. Earlier, we found that the rhythms of photosynthesis, phototaxis and cell shape followed the same pattern in control organisms, but were differently affected by stress such as UV‐B irradiation and nitrogen deficiency. Here we extend our studies to use isolated plasma membranes to characterize the rhythms of some plasma membrane‐bound enzymes. Also, we wanted to see whether stress‐induced changes of these rhythms could be detected at the subcellular level and possibly be coupled to the changes seen in photosynthesis, phototaxis and cell shape. The isolation of plasma membranes using aqueous polymer two‐phase partitioning was successful, as judged by the large enrichment of the plasma membrane‐marker 5′‐nucleotidase, and the difference in the polypeptide pattern compared with the microsomal fraction from which it was prepared.Two other enzymes were analyzed, K+, Mg2+‐ATPase, and adenylyl cyclase. The specific activities of all three enzymes were decreased by UV‐B radiation by ca 30–50%, compared with the control cultures. On the other hand, nitrogen deficiency not only reduced the activity of the K+.Mg2+‐ATPase but also increased the activities of the 5′‐nucleotidase and adenylyl cyclase. The different treatments also resulted in differences in polypeptide pattern, e.g., a polypeptide around 30 kDa seemed to be specific to plasma membranes of nitrogen‐deficient cultures and one at 39 kDa for the UV‐B radiated ones.All three enzymes showed diurnal rhythms that were affected by UV‐B radiation. The peak in the rhythm of the ATPase was shifted by UV‐B radiation, the rhythm of the 5′‐nucleotidase nearly eliminated. The first peak of adenylyl cyclase activity was delayed, so that it looked more like a broad peak between 2 and 11 h after the onset of light. The rhythm of ATPase activity could be correlated with that of photosynthesis in both control and UV‐B irradiated cultures. Also, the rhythms of adenylyl cyclase activity and cell shape changes showed some similarities.
Optimal leaf area indices in C3 and C4 mono‐ and dicotyledonous species at low and high nitrogen availability
Authors: Anten N. P. R. , Schieving F. , Medina E. , Werger M. J. A. , Schuffelen P. 
Published: May 2006

From an analytical model it was shown that for a given total amount of nitrogen in the canopy, there exists an optimal leaf area index (LAI), and therefore an optimal average leaf introgen content, at which canopy photosynthesis is maximal. If the LAI is increased above this optimum, increased light interception will not compensate for reduction in photosynthetic capacity of the canopy resulting from reduced leaf nitrogen contents. It was further derived from the model that the value of the optimal LAI increases with the photosynthetic nitrogen use efficiency (PNUE) and decreases with the canopy extinction coefficient for light (KL) and incident photon flux density (PFD) at the top of the canopy. These hypotheses were tested on dense stands of species with different photosynthetic modes and different architectures. A garden experiment was carried out with the C4 monocot sorghum (Sorghum bicolor [L.] Moensch cv. Pioneer), the C3 monocot rice (Oryza sativa L. cv. Araure 4), the C4 dicot amaranth (Amaranthus cruentus L. cv. K113) and the C3 dicot soybean (Glycine max [L.] Merr. cv. Williams) at two levels of nitrogen availability.The C4 species had higher PNUEs than the C3 species while the dicots formed stands with higher extinction coefficients for light and had lower PNUEs than the monocots. The C4 and monocot species were found to have formed more leaf area per unit leaf nitrogen (i.e., had lower leaf nitrogen contents) than the C3 and dicot species, respectively. These results indicate that the PNUE and the extinction coefficient for light are important factors determining the amount of leaf area produced per unit nitrogen as was predicted by the model.
Xyloglucan endotransglycosylase activity during fruit development and ripening of apple and kiwifruit
Authors: Percy Ann E. , O'Brien Iona E. W. , Jameson Paula E. , Melton Laurence D. , MacRae ELspeth A. , Redgwell Robert J. 
Published: May 2006

Xyloglucan endotransglycosylase (XET) activity was measured in apple (Malus domestica Borkh. cv. Braeburn) pericarp and kiwifruit (Actinidia deliciosa [A. Chev.] C. F. Liang et A. R. Ferguson var. deliciosa cv. Hayward) outer pericarp and core tissues in order to establish whether a correlation exists between the activity of the enzyme and different stages of fruit development Whereas the growth rate of kiwifruit paralleled changes in XET activity throughout fruit growth, that of apple did not. Both fruits showed the highest XET activity, on a fresh weight basis, in the first two weeks after anthesis when cell division was at its highest. XET activity then decreased sharply, but as the fruit increased in size (4–8 weeks after anthesis) there was a concomitant increase in XET activity in both fruits. In the latter stage of fruit development (16–26 weeks after anthesis) XET activity increased to peak at harvest in apple fruit. During this time there was relatively little increase in fruit size and presumably therefore minimal cell expansion. XET activity then declined as fruit softened after harvest. In core tissue from kiwifruit, XET activity increased throughout the later stages of fruit growth to harvest maturity in a similar manner to apple, but continued to increase after harvest until fruit were ripe. In contrast, XET activity in the outer pericarp of kiwifruit did not increase until ripening after harvest. In apple tissue up to 30% of the XET activity was cell wall bound and could not be solubilised, even in buffer containing 2 M NaCl.The results implicate XET in cell wall assembly during cell division and expansion early in apple and kiwifruit growth. However, the disparity between apple and kiwifruit with respect to XET activity late in fruit development and ripening and the different affinities of the enzyme for the cell wall in each fruit, suggest that XET has several roles in plant development, not all of which are related to cell wall loosening during periods of accelerated growth.
Differential expression of β‐conglycinin genes in nodulated and non‐nodulated isolines of soybean
Authors: Ohtake Norikuni , Suzuki Momoko , Takahashi Yoshihiko , Fujiwara Toru , Chino Mitsiio , Ikarashi Taro , Ohyama Takuji 
Published: May 2006

Nodulated (T202) and non‐nodulated (T201) isolines of soybean (Glycine max [L.] Merr.) were cultivated in a rotated paddy field in Niigata, Japan. The pods, and seeds were harvested at 7‐day intervals until maturity, and the subunit compositions of seed storage proteins were analyzed by SDS‐PAGE. The β‐subunit of β‐conglycinin could scarcely be detected in the non‐nodulated isoline, T201, at any period throughout seed development, although it was a major component in T202. The accumulation of α′‐ and α‐subunits of β‐conglycinin, together with the acidic and basic subunits of glycinin, appeared about one week later in seeds of T201 than in those of T202, perhaps due to a shortage of nitrogen and growth retardation. Northern hybridization could not detect the β‐subunit mRNA in immature T201 seeds, while it was pronounced in T202. These results indicate that the suppression of the β‐subunit in the non‐nodulating isoline T201 is regulated at the level of mRNA accumulation. The α′(α)‐subunit mRNAs were actively expressed in both isolines. Total nitrogen concentration was consistently lower in T201 than T202. No significant difference was observed in either the free amino acid or ureide concentrations in seeds, although the concentration of sucrose was considerably lower in T201 seeds and pods compared with T202. This result indicates the possibility that β‐subunit accunmlation was regulated not only directly by total nitrogen concentration but also by carbohydrate concentrations.Nitrogen regulation of storage protein subunit levels of soybean seed were evaluated using T201 and T202. Greenhouse‐grown plants were subjected to different levels and timing of nitrate treatments. The culture solution (2, 5 or 10 mM NO3–was supplied from flowering, 42 days after planting (DAP), until maturation (137 DAP), or switched from 2 to 10 mM, or from 10 to 2 mM at 61 DAP. With a continuous 2 mM NO3–treatment, seed dry weight and N concentration of the T201 plants were significantly lower than those in the T202 plants due to the lack of N2 fixation by the non nodulated T201 plants. However, when adequate NO3 was supplied, N concentration and dry weight were similar in T201 and T202 seeds. When 5 mM NO3 was supplied, the subunit proportion of the seed storage protein was similar in non‐nodulating and nodulating isolines. On the other hand, when plants received a low level of NO3 (2 mM), the β‐conglycinin proportion was lower in T201 than in T2O2. Furthermore, in the nodulating T202 plants treated with 10 mM NO3–the proportion of β‐conglycinin increased markedly.The results indicate that non‐nodulated T201 has a normal, non‐defective, β‐subunit gene and that limited N availability decreases accumulation of β‐conglycinin, whereas high N availability increases the proportion of β‐conglycinin in soybean seeds, irrespective of whether N was derived from N2 fixation or from NO3 absorption.
Random root movements in weightlessness
Authors: Johnsson Anders , Karlsson Christina , Iversen Tor‐Henning , Chapman David K. 
Published: May 2006

The dynamics of root growth was studied in weightlessness. In the absence of the gravitropic reference direction during weightlessness, root movements could be controlled by spontaneous growth processes, without any corrective growth induced by the gravitropic system. If truly random of nature, the bending behavior should follow socalled ‘random walk’ mathematics during weightlessness. Predictions from this hypothesis were critically tested.In a Spacelab ESA‐experiment, denoted RANDOM and carried out during the IML‐2 Shuttle flight in July 1994, the growth of garden cress (Lepidium sativum) roots was followed by time lapse photography at 1‐h intervals.The growth pattern was recorded for about 20 h. Root growth was significantly smaller in weightlessness as compared to gravity (control) conditions.It was found that the roots performed spontaneous movements in weightlessness. The average direction of deviation of the plants consistently stayed equal to zero, despite these spontaneous movements. The average squared deviation increased linearly with time as predicted theoretically (but only for 8–10 h).Autocorrelation calculations showed that bendings of the roots, as determined from the 1‐h photographs, were uncorrelated after about a 2‐h interval.It is concluded that random processes play an important role in root growth. Predictions from a random walk hypothesis as to the growth dynamics could explain parts of the growth patterns recorded. This test of the hypothesis required microgravity conditions as provided for in a space experiment.
Sucrose accumulation in developing peach fruit
Authors: Vizzotto Giannina , Pinton Roberto , Varanini Zeno , Costa Guglielmo 
Published: May 2006

Uptake of 14C‐sugars and activities of sucrose metabolizing enzymes were determined in order to study the mechanism(s) of sucrose accumulation in developing peach fruit. Mesocarp of young peach fruit contained glucose and fructose but little sucrose. Starting 88 days after anthesis (DAA) the sucrose concentration increased greatly. The mechanism of sucrose accumulation was studied by measuring 14C‐sucrose and 14C‐glucose uptake rates at three different stages of fruit development, and by assaying weekly the activity of enzymes involved in the hydrolysis and/or synthesis of the soluble sugars. Uptake of 0.5–100 mM14C‐sucrose and 14C‐glucose by mesocarp tissue slices showed a complex pattern at the first stage of fruit development (62 DAA). During the subsequent growth stages the pattern of sugar uptake changed and was approximately monophasic at the third stage of fruit development.At 10 mM, glucose was taken up more rapidly than sucrose at the first and second stage of fruit development. Uptake was partially inhibited by the uncoupler carbonylcyanide m‐chlorophenylhydrazone (CCCP) at 25 μM. These results, together with the presence of a putative extracellular invertase, suggest an apoplastic route for sucrose uptake which is dependent, at least in part, on energy supply.Activities of sucrose hydrolyzing enzymes (insoluble acid invertase, soluble acid invertase, neutral invertase, sucrose synthase) were high in young fruits and declined sharply with fruit development concomitantly with accumulation of sucrose. The storage of the sugar was not accompanied by a rise in synthetic activities (sucrose synthase, sucrose phosphate synthase), suggesting that sucrose could, at least in part enter the carbohydrate pool directly.
Changing root and shoot architecture with the rolA gene from Agrobacterium rhizogenes: Interactions with gibberellic acid and polyamine metabolism
Authors: Ben‐Hayyim Gozal , Martin‐Tanguy Josette , Tepfer David 
Published: May 2006

The effects of rolA on root and shoot architecture have been ascribed to a deficiency in gibberellic acid (GA3) and to changes in polyamine metabolism. Using tobacco, we examined interactions among GA3, a polyamine accumulation inhibitor (α‐DL‐difluoromethylornithine or DFMO) and the rolA gene controlled by the 35S CaMV promoter. We measured the effects of these three agents on architecture and polyamine accumulation in excised roots and whole plants grown in vitro. Previous work showed that DFMO or genetic transformation with the rolA gene from Agrobacterium rhizogenes, controlled by the 35S promoter (P35S‐rolA), caused excised tobacco roots to grow faster with altered root system architecture. We show that gibberellic acid (GA3) reversed the effects of DFMO on the architecture of excised root systems, but neither reversed the effects of DFMO on growth, nor the changes in growth and architecture associated with P35S‐rolA. GA3 treatment alone resulted in increased agmatine levels, suggesting that the inhibition of the effects of DFMO on architecture was through a stimulation of the arginine decarboxylase (ADC) pathway, GA3 alone also inhibited the accumulation of putrescine and tyramine conjugates in excised roots.In tobacco plants growing in vitro DFMO and P35S‐rolA were associated with reduced shoot height, which was partially restored by GA3 treatment; however, GA3 also stimulated shoot height in the controls. GA3 did not lessen the leaf wrinkling associated with P35S‐rolA. P35S‐rolA increased root number in young seedlings in vitro, and increased root system length in seedlings grown in soil. As in excised roots, the developmental changes linked to DFMO and P35S‐rolA were accompanied by reductions in putrescine titers. GA3 treatment stimulated putrescine accumulation in stems and leaves, and partially reversed the negative effects of DFMO and P35S‐rolA on putrescine accumulation in roots, stems and leaves. Again, the restoration of putrescine pools appeared to be through a stimulation of the ADC pathway, since agmatine accumulated in plants exposed to GA3. In general, the effects of DFMO and P35S‐rolA on phenotype and polyamine metabolism were coordinated, and in many cases these effects were similarly modulated by GA3, reinforcing the previous conclusion that the phenotypic effects of rolA in roots and shoots occur through interference with polyamine metabolism and that the putrescine conjugates are particularly important in regulating root system growth and architecture. We were unable, however, to discem consistent evidence for a direct role for GA3 in establishing the RolA phenotype.
Relationship between cavitation and water uptake in rose stems
Authors: van Doorn Wouter G. , Suiro Véronique 
Published: May 2006

Cavitation in rose stems (Rosa hybrida L.) was assessed in both intact plants and excised flowers, by measurement of ultrasonic acoustic emissions at the stem surface and determination of the air‐conductivity of 2.5‐cm segments that were attached at one end to air at low pressure (0.01 MPa). On sunny days the stems of intact rose plants showed acoustic emissions and conductivity to air, starting early in the morning. In Cara Mia and Sonia rose plants the cavitations were repaired during the late afternoon; in Madelon plants this repair only occurred overnight. Water flow was seriously impaired in stems of Cara Mia roses cut around midday, on sunny days.During dehydration of cut roses in air the onset of a high rate of acoustic emissions coincided with a low rate of water uptake when stems were subsequently placed in water. High emission frequency occurred after 2.4 ± 0.7 h, 6.8 ± 4.3 h and 19.8 ± 9.0 h of exposure to air in Cara Mia, Madelon and Sonia roses, respectively. A low rate of water uptake in excised stems placed in water was found after 3–4, 9–12 and 24–36 h of desiccation in air, respectively. The onset of the high emission frequency corresponded with a water potential of −1.7, −2.9 and −3.8 MPa in the three cultivars, respectively.It is concluded that a high number of cavitations may occur in noncut stems of rose plants, leading to low water uptake immediately after excision, depending on the weather and the cultivar, and that the low rate of water uptake after a period of dry storage, among the three rose cultivars investigated, is correlated with the presence of a high number of cavitated xylem elements.
Alternative oxidase from Arum and soybean: Its stabilization during purification
Authors: Zhang Qisen , Hoefnagel Marcel H. N. , Wiskich Joseph T. 
Published: May 2006

Complete purification of the alternative oxidase from plant mitochondria has not been achieved successfully, because of its instability on solubilization. We report here that the addition of pyruvate to the isolation medium stabilizes the activity of the solubilized enzyme. A procedure is described for the rapid isolation and partial purification of the cyanide‐insensitive alternative oxidase from both Arum maculatum and soybean cotyledon (Glycine max) mitochondria. The degree of purification was 16‐ and 74‐fold for Arum and soybean enzyme, respectively. The specific activities increased from 1 300 to 20 300 nmol oxygen consumed mg−1 protein min−1 (using duroquinol as substrate) after purification for the Arum erizyme and from 6 to 445 nmol oxygen consumed mg−1 protein min−1 for the soybean enzyme. A turnover for the partially purified Arum enzyme was estimated to be 47 electrons s−1.The partially purified enzyme from both Arum and soybean cotyledon mitochondria was sensitive to alternative oxidase inhibitors such as salicylhydroxamic acid, n‐propyl gallate and octyl gallate, but not to myxottriazol, KCN or antimycin A. The activity of the enzyme could be stimulated by pyruvate, but not by malate and suceinate. The stability of the purified enzyme was also dependent on the continued presence of pyruvate. In the absence of pyruvace, the enzyme activity was lost in a time‐dependent manner and the ability of pyruvate to recover the activity was also irreversibly lost.
The oxidative burst in plant defense: Function and signal transduction
Authors: Low P. S. , Merida J. R. 
Published: May 2006

The rapid production and accumulation of active oxygen species (AOS), the oxidative burst, has been shown to occur in a variety of plant/pathogen systems. In particular, two species, hydrogen peroxide (H2O2) and the superoxide radical anion O2− have received considerable attention. H2O2 and O2−, while acting directly as antimicrobial agents, may also serve as second messengers or catalysts in plants to activate a more diverse set of defense responses. Some of the better studied downstream responses promoted by AOS are (1) the cross‐linking of cell wall proteins, (2) the induction of defense‐related genes, (3) the stimulation of phytoalexin biosynthesis and (4) promotion of the hypersensitive response (HR).A useful model for studying the oxidative burst in plants is the neutrophil NADPH ox‐idase complex, the primary source of AOS production in mammals. Several of the subunits of the neutrophil NADPH oxidase complex have been immunologically identified in plants. Furthermore, many of the components known to be involved in the signal transduction pathway in neutrophils have also been found to play a role in the oxidative burst in plants. Just as various ligands activate the oxidase complex in neutrophils, several ligands (elicitors or pathogens) also lead to induction of the oxidative burst in plant cells. The similarities between the neutrophil and plant oxidative bursts will be elaborated in this review.Following stimulation with elicitors, different signal transduction pathways are activated in plants, depending on the source of elicitor used. While the identities and chronologies of the major intermediates in these pathways remain largely unknown, there is strong evidence at least for participation of phospholipases, H+/K+ exchange, Ca2+ influxes, protein kinases and phosphatases, and GTP binding proteins. In an effort to integrate these various signaling events into a single scheme, we have constructed a hypothetical model that proposes how different elicitors might induce the oxidative burst in the same cell by different pathways.