Sunflower Stem Research Articles

Erratum to the article “Sunflower stem: a novel and economical scavenger for Hg(II) ions from aqueous solutions and its kinetic and thermodynamic investigation” by Ummat Rasul Malik, Syed Moosa Hasany, Muhammad Sadiq Subhani

Erratum to the article “Sunflower stem: a novel and economical scavenger for Hg(II) ions from aqueous solutions and its kinetic and thermodynamic investigation” by Ummat Rasul Malik, Syed Moosa Hasany, Muhammad Sadiq Subhani

Sunflower stem: a novel and economical scavenger for Hg(II) ions from aqueous solutions and its kinetic and thermodynamic investigation

Summary The sorption of > 93% of Hg(II) ions is achieved onto sunflower stem (50 mg/4.5 cm3) from deionized water (D.W.) in 10 minutes equilibration time between two phases. The kinetics of sorption follows Reichenberg, Lagergren and Morris-Weber equations. The first order rate constant of sorption computed from Lagergren equation is 0.28 ± 0.01 min-1. The sorption data obey Dubinin–Radushkevich (D–R) and Freundlich isotherms. The Freundlich sorption capacity K F = 13 ± 6 mmol g-1, 1/n = 0.68 ± 0.03 and D–R saturation capacity C m = (2.9 ± 0.4)×102 μmol g-1, β = -0.0047 ± 0.0002 mol2 kJ-2 and mean free energy = 10.3 ± 0.2 kJ mol-1. The variation of sorption with temperature (293–318 K) gives ΔH = - 32 ± 2 kJ mol-1, ΔS = 123 ± 6 J mol-1 K-1, ΔG 298K = - 4.30 ± 0.05 kJ mol-1. Ascorbate, Sr(II) and Y(III) enhance the sorption whereas disufite, iodide, Cd(II), bisulfite and thiocyanate suppress the sorption. Selectivity studies indicate that Hg(II) ions can be separated from I(I) and Cs(I) using sunflower stem column. The sorbent may be used as a scavenger for the preconcentration of Hg(II) ions from its very dilute solutions or treatment of industrial and municipal effluents containing Hg(II) ions. A possible mechanism of biosorption of Hg(II) ions onto the sunflower stem is suggested.

Plasmid distribution in European Diaporthe helianthi isolates

Diaporthe helianthi is the causal agent of sunflower stem canker, a serious pathogen of sunflower in Europe, which has been sporadically recorded in Italy. A collection of 26 Diaporthe helianthi isolates deriving from different geographic origins was analysed in order to determine the presence of extra-chromosomal genetic determinants and their molecular diversity. Extra-chromosomal bands in total genomic DNAs were identified in every French and the Yugoslavian isolate and in only one Italian isolate, while no Romanian and Argentinean isolates resulted to host any plasmids. When tested for their chemicophysical nature, they were recognised as linear plasmids sized about 2.3 Kb. A more detailed analysis was performed on a plasmid purified from a French isolate (plasmid F). Its intracellular localisation resulted as mitochondrial. Plasmid F was also exploited as a probe in Southern hybridisation experiments, in which it recognised only plasmids present in the genomes of French and Yugoslavian isolates (countries were the disease has a heavy incidence) indicating a strong correlation to geographic origin. An RFLP hybridisation analysis performed on genomic DNAs revealed a homogeneous restriction pattern in all French and Yugoslavian isolates, suggesting molecular homology among plasmids present in those isolates.

Pleiotropic gene and its influence on stem, petiole and bract tip pigmentation in sunflower (Helianthus annuus L.)

SUMMARY The inheritance of stem, petiole and bract tip color was studied in the cross cms -103A × PFNB-2. F 1 studies revealed that purple color of stem, petiole and bract tip is dominant over green color of these plant parts. Complementary gene action was observed for these characters in F 2 . The genes governing the inheritance of stem, petiole and bract tip colors were designated as Ptla and Psmb, Ptla and Ptlb, Ptla and Pbtb, respectively, the gene Ptla being common to all three traits. RESUMEN La herencia del color del tallo, el pecíolo y el pico de la bráctea, era estudiada en el cruzamiento cms -103 A × PFNB-2. El estudio de la generación F 1 mostró que el color violeta del tallo, el pecíolo y el pico de la bráctea era dominante en relación con el color verde de dichas partes vegetales. Fue observada la acción complementaria de genes para estas propiedades en la generación F 2 . Los genes que dirigían la herencia del color del tallo, el pecíolo y el pico de la bráctea, fueron designados como Ptla y Psmb, Ptla y Ptlb y Ptla y Pbtb. El gen Ptla es común para todas las tres propiedades. RÉSUMÉ La transmission de la couleur de la tige, du pétiole et du sommet de la bractée a été étudiée dans le croisement cms -103 A × PFNB-2. Les études F 1 ont démontré que la couleur violette de la tige du pétiole et du sommet de la bractée était dominante par rapport à la couleur verte de ces parties de la plante. Pour ce qui est de ces caractéristiques, une action complémentaire du gène a été observée en F 2 . Les gènes qui gèrent la transmission de la couleur de la tige, du pétiole et du sommet de la bractée ont été respectivement désignés comme Ptla et Psmb, Ptla et Ptlb et Ptla et Pbtb. Le gène Ptla est commun aux trois caractéristiques.

Influence of Planting Date on Sunflower Stem Weevil (Coleoptera: Curculionidae) Larval Density and Parasitism in Oilseed and Confection Sunflower in Western Kansas

The sunflower stem weevil infests stalks of cultivated sunflower and can cause lodging resulting in loss of the head prior to harvest. Our objective was to determine whether altered planting periods could reduce weevil densities in confection and oilseed sunflower in the central High Plains production region. We evaluated impact of planting date by measuring larval density within sunflower stalks, larval parasitoid species present, and parasitization rates. Trials were conducted at Colby, KS from 1999 to 2001, with plots seeded in four planting periods. Results, although inconsistent over years and between the two sunflower types, showed that later planting dates reduced weevil density in stalks. Weevil numbers in stalks from the first seeding period until the last had decreased by 10% to 50%. The third planting date in each year coincided with cumulative degree-days (581) for the predicted emergence of 90% of adult sunflower stem weevils. Yields were not reduced as planting was delayed. Fewer weevils were observed in oilseed than in confection hybrids. Lower densities of sunflower stem weevils in the stalk can reduce losses from lodged plants. Seven hymenopteran parasitoid species were reared from sunflower stem weevil larvae. Nealiolus curculionis (Fitch) and Neocatolaccus tylodermae (Ashmead) were the most common species. Parasitization rates were low, but wasps actively attacked the weevil throughout the growing season. Research showed that delaying planting until after the early and later May planting periods reduced weevil densities in western Kansas.

Sorptive potential of sunflower stem for Cr(III) ions from aqueous solutions and its kinetic and thermodynamic profile

The sorptive potential of sunflower stem (180–300 μm) for Cr(III) ions has been investigated in detail. The maximum sorption (≥85%) of Cr(III) ions (70.2 μM) has been accomplished using 30 mg of high density sunflower stem in 10 min from 0.001 M nitric and 0.0001 M hydrochloric acid solutions. The accumulation of Cr(III) ions on the sorbent follows Dubinin–Radushkevich (D–R), Freundlich and Langmuir isotherms. The isotherm yields D–R saturation capacity X m = 1.60 ± 0.23 mmol g −1, β = −0.00654 ± 0.00017 kJ 2 mol −2, mean free energy E = 8.74 ± 0.12 kJ mol −1, Freundlich sorption capacity K F = 0.24 ± 0.11 mol g −1, 1/ n = 0.90 ± 0.04 and of Langmuir constant K L = 6800 ± 600 dm 3 mol −1 and C m = 120 ± 18 μmol g −1. The variation of sorption with temperature (283–323 K) gives Δ H = −23.3 ± 0.8 kJ mol −1, Δ S = −64.0 ± 2.7 J mol −1 K −1 and Δ G 298k = −4.04 ± 0.09 kJ mol −1. The negative enthalpy and free energy envisage exothermic and spontaneous nature of sorption, respectively. Bisulphate, Fe(III), molybdate, citrate, Fe(II), Y(III) suppress the sorption significantly. The selectivity studies indicate that Cr(III), Eu(III) and Tb(III) ions can be separated from Tc(VII) and I(I). Sunflower stem can be used for the preconcentration and removal of Cr(III) ions from aqueous medium. This cheaper and novel sorbent has potential applications in analytical and environmental chemistry, in water decontamination, industrial waste treatment and in pollution abatement. A possible mechanism of biosorption of Cr(III) ions onto the sunflower stem has been proposed.

A coding region in Diaporthe helianthi reveals genetic variability among isolates of different geographic origin.

A set of Diaporthe helianthi isolates collected in different geographic areas was studied in order to examine whether different genetic biotypes could be responsible for epidemiological differences shown by sunflower stem canker. D. helianthi causes serious losses in France and in former Yugoslavia, while the pathogen is only sporadically recorded in Italy in spite of conducive pedoclimatic conditions. Variability of a D. helianthi coding genomic region, evaluated by means of polymerase chain reaction (PCR), Southern blot hybridisation and restriction fragments length polymorphism (RFLP), showed a conserved homogeneous pattern shared by French and Yugoslavian isolates compared with the heterogeneous pattern of Italian isolates. These results are consistent with other investigations (IGS and ITS region variability) performed on the same set of isolates, allowing a correlation between D. helianthi biotypes, their geographic origin and sunflower stem canker epidemiology.

Intraspecific Diversity within Diaporthe Helianthi: Evidence from Rdna Intergenic Spacer (IGS) Sequence Analysis

Diaporthe helianthi is the causal agent of sunflower stem canker, a serious pathogen of sunflower in Europe but recorded sporadically in Italy. The genetic diversity of D. helianthi isolates from different geographic origins (Argentina, France, Italy, Yugoslavia, Romania) was investigated using IGS sequences. A 400 bp fragment of the portion of the IGS region flanking the 5' end of the 18S gene was amplified from each isolate. The aligned nucleotide sequences showed intraspecific sequence homology from 99-100% among French/Yugoslavian isolates to 95-100% among Italian isolates. French/Yugoslavian isolates shared 90-92% sequence homology with Italian isolates. The phylogenetic tree obtained from the aligned data revealed three separate groups. Group 1 included all isolates from France and former Yugoslavia and one isolate from Argentina; Group 2 included all Italian isolates and one isolate from Argentina. The most distantly related isolate was that from Romania (Group 3). The average genetic distances among isolates within Group 1 and within Group 2 were 0.22 and 3.29 respectively. The analysis showed that all isolates originating from countries where severe outbreaks of the disease are reported annually (France and former Yugoslavia) form a well defined taxon characterized by relatively low variability. This group is distinct from the group formed by isolates originating from Italy, whose variability is relatively much higher. Results obtained revealed a marked differentiation among pathogen isolates, and members of Group 1 seem not yet to have spread into Italian sunflower-growing areas.

Polymorphisms in nuclear rDNA and mtDNA reveal the polyphyletic nature of isolates of Phomopsis pathogenic to sunflower and a tight monophyletic clade of defined geographic origin

The molecular diversity of Diaporthe helianthi (anamorph Phomopsis helianthi), the causal agent of sunflower stem canker, was studied in 16 isolates of different geographic origin using nuclear and mitochondrial markers. PCR products corresponding to the internal transcribed spacers (ITS1 and ITS2) of the nuclear ribosomal RNA gene, and to the mitochondrial atp6 gene were sequenced. The ITS1 and ITS2 sequences were compared with those of Phomopsis spp. and Diaporthe spp. obtained from databases. The diversity in the region surrounding the atp6 gene was also studied by restriction analysis using four enzymes. The analyses revealed a marked diversity within the sunflower-isolated strains, which appear to belong to phylogenetically unrelated groups. Noticeably, all the isolates collected in France and in the former Yugoslavia, where severe epiphytotics of sunflower stem canker are frequently reported, showed high similarity to each other forming a clade which clearly differentiated from all other ones within the genus Phomopsis. Conversely, all the isolates collected in Italy, where, despite favourable environmental conditions, the incidence of the disease is low, were only distantly related to the former group and showed sequence similarity with other previously established phylogenetic clades within the Phomopsis/Diaporthe complex.

Influence of crop management on sunflower stem canker (Diaporthe helianthi)

Le phomopsis du tournesol, maladie cryptogamique causee par Diaporthe helianthi Munt.-Cvet. et al., est responsable de pertes de rendement pouvant atteindre 40 %. Au travers d'une collaboration INRA-Cetiom (1994-2000), les effets de la conduite de culture du tournesol sur la frequence et la gravite des attaques de phomopsis ont ete etudies experimentalement dans la region toulousaine. Il a ete montre que la densite de peuplement augmente la proportion de tiges presentant des taches de phomopsis. Par contre, l'augmentation des doses d'azote peut se traduire dans certaines conditions par une diminution de la frequence de tiges attaquees. Le retard de semis reduit le risque de contamination foliaire et de degât sur tige. Des conduites integrant ces techniques ont ete evaluees pendant 7 annees : si la strategie de rationnement vegetatif (reduction de la densite de peuplement et de la fertilisation azotee) n'est pas suffisante a elle seule pour maitriser le phomopsis, son association avec le semis tardif permet d'atteindre des niveaux d'attaque proches de ceux obtenus en semis precoce, proteges chimiquement. La rentabilite des conduites « bas intrants », ne recevant pas de fongicides, n'est assuree que si l'on utilise des varietes peu a tres peu sensibles et en l'absence de forte hygrometrie en juin.

First Report of Charcoal Rot (Macrophomina phaseolina) on Sunflower in North and South Dakota.

In September 1998, symptoms suggestive of charcoal rot were observed on oilseed sunflower (Helianthus annuus L.) plants in western North and South Dakota. Symptoms first observed on plants approaching physiological maturity consisted of silver-gray lesions girdling the stem at the soil line, premature plant death, and reduced head diameter. The pith in the lower stem was completely absent or compressed into horizontal layers. Black, spherical microsclerotia were observed in the pith of the lower stem, underneath the epidermis, and on the exterior of the taproot. Confirmation of Macrophomina phaseolina (Tossi) Goid. as the causal agent was based on the size of the microsclerotia, which ranged from 80 to 90 μm in diameter, from both infected sunflowers and pure cultures (1). The only other sunflower pathogen known to form microsclerotia is Verticillium dahliae Kleb., whose microsclerotia are irregular in shape and are 15 to 50 μm in diameter. Some prematurely dead sunflower plants lacked typical charcoal rot stem lesions, but contained Macrophomina microsclerotia. Plants with atypical symptoms were colonized by the sunflower stem weevil (Cylindrocopturus adspersus (LeConte)) and the black sunflower stem weevil (Apion occidentale Fall). This agrees with observations in Texas, where Macrophomina-infected sunflower plants parasitized by stem-feeding insects often displayed atypical charcoal rot symptoms (3). Charcoal rot incidence in 1998 in western North Dakota was 25%, compared with 0% in eastern North Dakota. Charcoal rot was not observed in 1999, the fourth wettest growing season on record, but was observed again in 2000 and 2001. The recent increase in sunflower production in western North and South Dakota, areas typically hotter and drier than the eastern portions of both states, and the potential involvement of stem weevils as vectors of Macrophomina (2) may lead to an increased incidence of charcoal rot in sunflower.

A QTL analysis of sunflower partial resistance to downy mildew ( Plasmopara halstedii) and black stem ( Phoma macdonaldii) by the use of recombinant inbred lines (RILs).

Partial resistance to downy mildew ( Plasmopara halstedii) and to black stem (Phoma macdonaldii) in sunflower were investigated under natural field infection and a controlled growth chamber respectively. Genetic control for resistance to the diseases was determined in recombinant inbred lines (RILs) and their two parents, 'PAC-2' and 'RHA-266.' The experiments were undertaken in a randomized complete block design with two replications, in a field severely infected by downy mildew and in a controlled growth chamber with plants inoculated with an agressive French isolate of P. macdonaldii. Each replication consisted of three rows, 4.6-m long, giving 48 plants per RIL or parent in the field and 15 plants in the growth chamber. Genetic variability was observed among the RILs for resistance to both diseases. When 10% of the selected RILs were compared with the mean of the two parents genetic gain was significant for partial resistance to the diseases. Four putative QTLs for resistance to downy mildew on linkage groups 1, 9 and 17 were detected using composite interval mapping. The QTLs explained 54.9% of the total phenotypic variance. Major QTLs ( dmr1-1 and dmr1-2) for resistance were found on linkage group 1 with up to 31% of the phenotypic variability explained by two peaks. QTL analysis of resistance to black stem showed seven QTLs on linkage groups 3, 6, 8, 9, 11, 15 and 17. The detected QTLs together explain 92% of the phenotypic variation of the trait. Crosses between RILs contrasted for their resistance to downy mildew and black stem, and exhibiting molecular polymorphism in detected QTLs, will be made in order to focus more-precisely on the genomic region of interest.

Sunflower stem weevil and its larval parasitoids in the Central and Northern Plains of the USA

The sunflower stem weevil, Cylindrocopturus adspersus (LeConte) (Coleoptera:Curculionidae), is apest of cultivated sunflower (Helianthusannuus L) from the southern to the northernGreat Plains. The incidence of weevilinfestation in fields from the six differentstates sampled during 1996 and 1997 ranged from33% (Minnesota) to 100% (Kansas, Colorado,Nebraska). Weevil populations in the fieldssampled were statistically greater in thecentral Plains (Colorado, Kansas, Nebraska)with a mean of 12.3 and 19.5 larvae per stalkcompared with the northern Plains (North andSouth Dakota, Minnesota) of 0.7 and 1.3 larvaeper stalk in 1996 and 1997, respectively.Parasitization of weevils varied from field tofield ranging from 1 to 100%, but was usuallyless than 20%. The nine species oflarval parasitoids recovered were allHymenoptera and included: Nealioluscurculionis (Fitch), N. collaris(Brues), Bracon sp. (Braconidae); Neocatolaccus tylodermae (Ashmead), Chlorocytus sp., Pteromalus sp.(Pteromalidae); Quadrastichus ainslieiGahan (Eulophidae), Eurytoma tylodermatisAshmead (Eurytomidae); and Eupelmus sp.(Eupelmidae). Nealiolus curculionis wasthe most prevalent parasitoid reared from C. adspersus, and it was recovered from allstates sampled. Parasitoid species richness wasgreatest in the central Plains. Thereduced number of parasitoid species foundattacking C. adspersus in the northernPlains may be caused by low host populationlevels, slow migration by parasitoids into theregion, or lack of adaptation to climaticconditions. Additional work to understandthe population dynamics of the parasitoidcomplex associated with C. adspersus mayresult in improved biological control of thesunflower stem weevil in cultivatedsunflower.

Inheritance of partial resistance to black stem (Phoma macdonaldii) in sunflower

Two programmes to investigate the inheritance of resistance to black stem in sunflowers were undertaken in a controlled-environment growth chamber. In the first, an experiment was performed using a randomized complete block design with 24 lines, six male-sterile (A lines), six maintainers (B lines), six restorers (R lines) and their six F1 hybrids in six replications. Each treatment consisted of 12 seedlings. Twelve-day-old seedlings were inoculated with a suspension of pycniospores, and 7 days later the two cotyledon petioles of each seedling were scored on a 1–9 scale for the percentage of necrotic area. Some alloplasmic lines (which have the same nucleus and different cytoplasms) gave a significant cytoplasmic effect for improved partial resistance to the disease. Deviation of F1 hybrids from the mean of the parent values was significant for partial resistance to Phoma macdonaldii in three of the six F1 hybrids. Two further experiments with eight lines (resistant and susceptible) at the fifth leaf-pair and flowering stages were carried out under the same conditions. At both growth stages the previous classification of lines at the seedling stage was confirmed. In the second programme, five male-sterile sunflower lines were crossed with five fertility-restorers in a factorial mating design. The 10 inbred lines and their 25 F1 hybrids were studied in two successive experiments under the same conditions and with the same experimental design and isolate of Phoma as in the seedling-stage experiment in the first programme. Analysis of variance showed that male-sterile and restorer lines possessed general combining abilities, and also that specific combining abilities of F1 hybrids were significant. The estimates of general combining ability for partial resistance were significant in AS617A, AS618A and AS614R inbred lines. These lines are available for developing F1 hybrids with improved resistance to Phoma in sunflower-breeding programmes.

669 Greenhouse Vegetable Production in China

There was a remarkable growth in China's greenhouse horticulture during the past decade. In 1989, the greenhouse area in China was 22,000 ha, but this figure reached up to 350,000 ha in 1999, about 16 times as large as that in 1989. Currently, the main greenhouse design used for commercial production is the energy conservation type—solar greenhouse—and many growers use eco-organic soilless culture for production. The substrates used for vegetable production are perlite, vermiculite, peat, coal cinder, sand, coir, sunflower stem, and sugar cane stem. Dry solid organic manure is mixed into the substrates before conducting cultivation, and then only water is for irrigation. Growing vegetables in this way improved quality, increased market value, and decreased environmental pollution.

Resistance in the leaf and stem of sunflower after infection with two isolates of Phomopsis

Abstract Phomopsis helianthi (sexual stage Diaporthe helianthi) is a major disease in most sunflower growing countries. The objectives of this study were (1) to investigate whether resistance to Phomopsis differs between the leaf and stem tissue and (2) to examine the genetic variation for resistance to Phomopsis in sunflower inbreds. A set of 16 inbred lines was tested using artificial leaf infection with mycelial explants. The lines were screened for their reaction on leaf and stem in four environments to a French Phomopsis isolate and in two environments to a Yugoslavian isolate. Significant genetic variance and mostly high genetic ratios (analogous to heritability) were found for all resistance traits. While fungal growth reflected resistance to Phomopsis in the leaf, petiole score was associated with leaf length. Stem lesion proved to be the most suitable trait for evaluating resistance in the petiole‐stem passage. No correlation existed between resistance in the leaf and stem, suggesting that both resistance factors are inherited independently. Both isolates resulted in similar resistance rankings of the inbreds and no difference in their aggressiveness was detected with regard to leaf resistance. Screening for Phomopsis consisting of several steps is recommended, beginning with petiole score or fungal growth to select the most susceptible plants in the early testing, and measuring stem lesion in further generations of breeding.

Very long-chain methyl-branched alcohols and their acetate esters in pupal internal lipids of developing Coleoptera, Anthonomus grandis and Cylindrocopturus adspersus, and Diptera, Cochliomyia hominivorax and Musca domestica

Mono- and dimethyl-branched primary alcohols from C28 to C56 were identified in the internal lipids of developing mid-stage pupae of two species of Coleoptera; the boll weevil, Anthonomus grandis and the sunflower stem weevil, Cylindrocopturus adspersus, and of two species of Diptera; the screwworm, Cochliomyia hominivorax, and the house fly, Musca domestica. Novel very long-chain dimethyl-branched alcohols (VLMA; C36–C56) were characterized for the first time in these two orders. The major VLMA component was 26,38-dimethylpentacontanol in the boll weevil, 28,38-dimethylpentacontanol in the sunflower stem weevil, and 26,36-dimethyloctatetracontanol in both the screwworm and house fly. These alcohols were six to ten carbons longer than similar alcohols previously reported for Lepidoptera. No terminally-branched or trimethyl-branched alcohols similar to those previously characterized in Lepidoptera were detected.

Evaluation of Planting Treatments for Sunflower Stem Weevil Control, 1997

Abstract Sunflower test plots were planted 14 May at the Central Great Plains Research farm 4 miles east of Akron, CO. Plots were 4 rows wide (22-inch row spacing) by 50 ft long and arranged in a RCB with four replications. The two row planter was calibrated to plant 18,000 seeds/acre. The soil type was a Weld silt loam. Gaucho 480°F seed treatment was applied at three rates; (8.2, 12.3, and 16.4 oz (AI)/cwt seed). Furadan 4°F was injected in the seed furrow at planting immediately following seed placement and prior to planter press wheels in a 1:1 (water:Furadan 4 F) dilution using a microinjection unit. Evaluations for lodged plants were made on 27 Sep by counting all plants in the center 2 rows followed by counting the number lodged. Mature SSW larvae were counted by dissecting four stalks from each plot on 15 Oct. Only the lower 18 inches of stalk was dissected. The diam of each stalk was measured at the cotyledon scars. The center two rows of each plot were hand harvested and thrashed. Yield data are adjusted to 10% moisture.

Interaction between proteins containing homeodomains associated to leucine zippers from sunflower

A strategy based on the use of PCR with one degenerate oligonucleotide deduced from conserved sequences and lambda gt10 primers was used to isolate homeobox containing sequences from sunflower stem and root cDNA libraries. Six different partial cDNAs coding for the first 48 amino acids of homeodomains and amino terminal sequences were analyzed and found to be members of the HD-Zip superfamily, which contain a homeobox linked to a leucine zipper coding region. A full-length cDNA clone, Hahb-10, was isolated and characterized. The leucine zipper portions of Hahb-10 and of the previously reported Hahb-1 have been utilized to construct fusions with the N-terminal domain of the lambda repressor. These fusions were tested for their ability to bind to lambda promoters in vivo. The expression of a protein containing an active dimerization domain, but not capable of DNA binding, exerts a dominant negative effect on the ability of repressor-zipper fusions to bind to its target DNA. From these experiments, it was concluded that Hahb-1 and -10, when co-expressed, form preferentially homodimers. Exchange of conserved threonines and leucines at positions a 1 and d 1 of both zippers reduces dimerization efficiency and allows the formation of heterodimers, suggesting that these residues are, among others, determinants of the specificity of interaction, most likely through changes in hydrophobic packing interactions at the dimer interface. The results imply that a great number of interacting molecular entities compose this protein superfamily which is presumably involved in regulating plant developmental responses.

Reduction of ferric iron by tumorous crown gall tissue is associated with cells modified byagro‐bacterium tumefaciens

Abstract Iron (Fe) uptake and use in plants is genetically controlled and physiological mechanisms such as Fe reduction are induced during Fe‐deficiency stress to make it available. Transfer of DNA into the cell genome by Agrobacterium tumefaciens alters physiological processes and causes undifferentiated growth. Tumor cells in sunflower (Helianthus annus L. cv. Mammoth Russian) show enhanced Fe reduction compared to normal stem tissue in a manner similar to root cells in plants that are genetically switched on or off to manage Fe acquisition. This study addresses whether alterations caused by the DNA transfer from A. tumefaciens result in Fe reduction or whether A. tumefaciens inoculum alone reduces Fe. Reduction of Fe was quantified from A. tumefaciens inoculum and from uninoculated or inoculated sunflower stem tissues daily over a 14‐day period. Neither A. tumefaciens inoculum nor uninoculated stem tissue alone activated massive Fe reduction. High rates of Fe reduction were associated with the prolifer...