A microsatellite marker in Helianthus annuus L.

The importance of genetic polymorphism detected by microsatellites is now well established in mammalian genomes. Sequences with a CA repeat, specific to sunflower, Helianthus annuus L., were found by screening a genomic library in M13. After amplification, some polymorphism was detected on these sequences within a sample of cultivars and populations.     

Ent-Kaurene Biosynthesis in Extracts of Helianthus annuus L. Seedlings

Kaurene synthetase B activity (conversion of copalyl pyrophosphate to ent-kaurene) is readily detectable in crude cell-free extracts of 3- to 4-day old dark-grown sunflower (Helianthus annuus cv. Mammoth) seedlings, whereas little or no kaurene synthetase AB activity (conversion of geranylgeranyl pyrophosphate to ent-kaurene) can be found in these extracts under comparable assay conditions. A low amount of AB activity is evident only if an extensively dialyzed extract is used in low concentrations as the enzyme source. One factor which may contribute to the low apparent levels of AB activity is the presence of inhibitory factors in the crude sunflower extract since these extracts can be shown to act as a potent inhibitor of Marah macrocarpus endosperm kaurene synthetase AB activity. Heat treatment (100°C) or dialysis of the sunflower extract reduces the amount of its inhibitory activity. Also, it was observed that low concentrations of extensively dialyzed sunflower extracts act to stimulate M. macrocarpus AB activity. There is no evidence for the presence of an inhibitory factor for M. macrocarpus kaurene synthetase B activity in sunflower extracts. However, there does appear to be present in the crude preparation of sunflower extract a dialyzable factor(s) that impedes its own B activity. There is little information to date on the nature of these inhibitory and stimulatory factors for kaurene synthetase activity or their possible roles in physiological regulation. The possible presence of such factors should be considered, however, when attempting to evaluate kaurene synthetase activities in extracts of vegetative plants.     

The domestication of Helianthus annuus L. (sunflower)

All modern domesticated sunflowers can be traced to a single center of domestication in the interior mid-latitudes of eastern North America. The sunflower achenes and kernels recovered from six eastern North American sites predating 3000 b.p. that document the early history of this important crop plant are reanalyzed, and two major difficulties in the interpretation of archaeological sunflower specimens are addressed. First, achenes and kernels obtained from a modern wild sunflower population included in a prior genetic study because of its minimal likelihood for crop-wild gene flow, and its close genetic relationship to domesticated sunflowers, provide a new and more tightly drawn basis of comparison for distinguishing between wild and domesticated achene and kernel specimens recovered from archaeological contexts. Second, achenes and kernels from this modern wild baseline population were carbonized, allowing a direct comparison between carbonized archaeological specimens and a carbonized modern wild reference class, thereby avoiding the need for the various problematic shrinkage correction conversion formulas that have been employed over the past half century. The need for further research on museum collections is underscored, and new research directions are identified.     

Longitudinal variation in cadmium influx in intact first order lateral roots of sunflower (Helianthus annuus. L)

Aims

Contamination of sunflower (Helianthus annuus L.) by cadmium (Cd) is a concern for food and feed safety as this species accumulates Cd to a greater extent than other crops. We examined the relationships between root architecture and Cd²⁺ uptake by roots.

Methods

We determined and mathematically modelled the longitudinal variation of Cd²⁺ influx in first order roots of sunflower grown in hydroponics by using short-term exposure to ¹⁰⁹Cd-labelled solutions (0.8 to 500 nM). Thereafter, by taking into account the longitudinal variation of the influx, we simulated the uptake of Cd²⁺ for 24 h by cohorts of roots characterised by various architectural characteristics.

Results

Cd²⁺ influx at the root tip was on average 2.9 times that of the basal region close to the taproot. The simulations indicated that the total Cd²⁺ uptake by root cohorts mainly depends on 1/ the root diameter and the number of roots, 2/ the value of the Cd²⁺ influx at the basal region 3/ the stronger influx at the root tip.

Conclusion

Considering a higher Cd²⁺ influx at the root tip may be important to understand the relationship between root architecture and Cd²⁺ uptake by the root system.     

Polyamines in Helianthus annuus L. during Germination under Salt Stress

The level of the three main polyamines putrescine, spermidine, and spermine and the biosynthetic enzyme arginine decarboxylase (ADC) decreased in Helianthus annuus L. seedlings subjected to increasing (50, 100, and 150 mm) NaCl concentrations. The pattern of polyamines in control plants increased during the initial 72 h and then reached a plateau. The putrescine level showed an increase of 370% after 72 h of development. The lower salt treatment slightly diminished the overall polyamine content. The highest NaCl concentration (150 mm) induced a strong putrescine diminution (from 381 to 78.9 nmol g⁻¹ FW) at 72 h whereas a small decrease in ADC activity was detected. ODC was detected in neither control nor treated plantlets during the experimental period. The level of spermidine also decreased, but the magnitude of the decay was less pronounced than putrescine. The fact that ODC was not detected and ADC activity followed a pattern similar to that of putrescine led us to suppose that the variation in putrescine content could be attributed entirely to the decrease in ADC activity. α-Difluoromethylarginine and α-difluoromethylornithine (ADC and ODC inhibitor, respectively) did not inhibit but delayed the onset of germination of sunflower seeds, and α-difluoromethylornithine increased the content of spermidine and spermine. The present data suggest that polyamines could be involved in the germination process of H. annuus seeds and in response to salt stress. Received April 14, 1997; accepted July 10, 1997     

Autosyndesis and structural hybridity in F1-hybrid Helianthus tuberosus L. x Helianthus annuus L. and their sequences

Summary Meiosis in F₁-hybridHelianthus tuberosus (n=51) xH. annuus (n=17) was studied. At least five inversions were determined with certainty. The genom formula ofH. tuberosus should be At₁At₂Bt/At₁At₂Bt and that ofH. annuus-Ba/Ba. Genom formula of F₁-hybrid is At₁Bt/At₂Ba, the chromosomes of Ba-genom conjugating with those of Bt-genom, while the other chromosomes of the other two genoms (At₁ and At₂) conjugating autosyndetically.Cytogenetic indices for producing plants combining characters ofH. tuberosus andH. annuus are discussed.     

Cell-wall synthesis and elongation growth in hypocotyls of Helianthus annuus L.

The relationship between growth and increase in cell-wall material (wall synthesis) was investigated in hypocotyls of sunflower seedlings (Helianthus annuus L.) that were either grown in the dark or irradiated with continuous white light (WL). The peripheral three to four cell layers comprised 30–50% of the entire wall material of the hypocotyl. The increase in wall material during growth in the dark and WL, respectively, was larger in the inner tissues than in the peripheral cell layers. The wall mass per length decreased continuously, indicating that wall thinning occurs during growth of the hypocotyl. When dark-grown seedlings were transfered to WL, a 70% inhibition of growth was observed, but the increase in wall mass was unaffected. Likewise, the composition of the cell walls (cellulose, hemicellulose, pectic substances) was not affected by WL irradiation. Upon transfer of dark-grown seedlings into WL a drastic increase in wall thickness and a concomitant decrease in cell-wall plasticity was measured. The results indicate that cell-wall synthesis and cell elongation are independent processes and that, as a result, WL irradiation of etiolated hypocotyls leads to a thickening and mechanical stiffening of the cell walls.     

Regeneration of fertile interspecific hybrids from protoplast fusions between Helianthus annuus L. and wild Helianthus species

The use of interesting characteristics from wild Helianthus species in sunflower breeding is limited by poor crossability or sterility of interspecific hybrids. To overcome this barrier, mesophyll protoplasts of Sclerotinia sclerotiorum-resistant clones of Helianthus maximiliani, H. giganteus and H. nuttallii were fused with hypocotyl protoplasts of H. annuus in the presence of polyethyleneglycol and dimethylsulfoxide. Fusion products were embedded in agarose and subjected to a regeneration protocol developed for sunflower protoplasts. Organogenic calli were transferred onto solid medium and emerging shoots were elongated in the absence of plant growth regulators. Rooting of shoots was induced by a 1-naphthaleneacetic acid treatment and putative hybrid plants from fusions between H. annuus + H. maximiliani and H. annuus + H. giganteus were transferred into the greenhouse. All of them exhibited a hybrid phenotype with a high percentage of rhizome producing plants. Their hybrid origin was confirmed by random amplified polymorphic DNA analysis. Plants flowered after 3–4 months and set seeds, of which 70–80% germinated. Received: 18 February 1997 / Revision received: 25 March 1997 / Accepted: 15 May 1997     

Accumulation of copper by roots,hypocotyls, cotyledons and leaves of sunflower (Helianthus annuus L.)

The effects of different concentrations of copper sulfate on the growth of and the accumulation of Cu2+ by root, hypocotyl, cotyledon and leaf growth of sunflower (Helianthus annuus L.) were examined in this study. The concentrations of copper sulfate (CuSO4 x 5H2O) used were in the range from 10(-5) to 10(-3) M. Seedlings exposed to 10(-5) M Cu2+ solution exhibited a 33% increase in growth (P < 0.005) when compared with the root length of the control. The seedlings treated with 10(-3) M Cu2+ were significantly inhibited in shoot growth (P < 0.005). The Cu2+ content in roots, hypocotyls, cotyledons and leaves increased with increasing solution Cu2+ concentration. The roots of plants exposed to 10(-3) M Cu2+ accumulated a large amount of Cu (1070 microgram/g DW), and the Cu2+ level was approximately 25 fold higher than that of control. The Cu2+ contents in sunflower roots treated with 10(-4) and 10(-5) M Cu2+ were about 3.3 and 2.6 fold higher than the control, respectively. Also, the Cu2- level of the roots exposed to 10(-3) M Cu2+ was approximately 7.7 and 9.8 fold respectively, in comparison with the roots of plants grown in 10(-4) and 10(-5) M Cu2+. At 10(-3) M Cu2+, the Cu accumulated mainly in the roots (about 73%), and small amounts of Cu2+ (27%) were translocated to the hypocotyls, cotyledons and leaves. The Cu2+ concentration in the roots was less than that of the above parts of seedlings in treated groups with 10(-5) - 10(-4) M Cu2+. H. annuus has potential ability to accumulate Cu without being overly sensitive to Cu toxicity.     

Production of asymmetric somatic hybrid plants between Cichorium intybus L. and Helianthus annuus L.

In order to obtain male-sterile asymmetric somatic hybrids between chicory (Cichorium intybus L.) and a sunflower (Helianthus annuus L.) male-sterile cytoplasmic line, mesophyll chicory protoplasts inactivated with iodoacetic acid and hypocotyl sunflower protoplasts irradiated with γ-rays have been fused, using PEG and applying two different procedures. Thirty three plants were regenerated from putative hybrid calli. A cytological analysis of their root-tip cells indicated that most of them had 18 chromosomes, the same number as chicory. Through Southern hybridisation on total DNA using the maize mitochondrial specific gene probes Cox I, Cox II and Cob, three plants were identified as cytoplasmic asymmetric hybrids, as shown by hybridisation bands specific for both chicory and sunflower. One of the regenerated plants produced a novel pattern of hybridisation that was not detected in either parent. When hybridisation of total DNA was carried out with an atpA mitochondrial gene probe the same three cybrids presented both the fertile chicory fragment and the male-sterile sunflower fragment. Finally, Southern hybridisation with an ORF 522 probe, which in sunflower is co-transcribed with the atpA gene, confirmed the hybrid nature of the three plants. The morphology of the cybrids resembled the parental chicory phenotype, and at anthesis their anthers produced fewer pollen grains which could not germinate either ”in vitro” or ”in situ.” Cybrid plants grown in the field produced seeds when free-pollination occurred. Received: 26 April 2000 / Accepted: 28 August 2000     

Root lodging tolerance in Helianthus annuus (L.): associations with morphological and mechanical attributes of roots

Background and aims

The objectives of this study were to quantify the morphological and mechanical properties of the root-plate within two sunflower hybrids of contrasting susceptibility to root lodging; and to evaluate the effects of crop population density on these properties at two different development stages.

Methods

Two hybrids (CF29: tolerant, Zenit: sensitive) were grown at three densities: 5.6, 10 and 16 plants m^?2. At R2 (early reproductive) and R6 (end anthesis) development stages, plants were artificially lodged and stem biomass, total root biomass in the whole root-plate and in the 0–5 and >5 cm layers of the plate, root number (three diametrical categories: 0–1, 1.1–2, >2 mm), total root length, and root axial breakage force were assessed.

Results

CF29 root mass was twice that of Zenit with differences mainly in the top 5 cm of soil. This higher root-plate biomass of CF29 was associated with a greater root number and root length compared to Zenit within all root diameter categories. Roots of CF29 exhibited higher axial tension failure thresholds than those of Zenit, and these thresholds increased more sharply with root diameter in CF29 than in Zenit.

Conclusions

The better anchorage and tolerance to lodging of CF29 with respect to Zenit arose from additive actions of traits at both whole root-plate and individual root levels. These included total root-plate root length, root number, root biomass and root axial breakage force.     

The mechanics of anchorage in seedlings of sunflower, Helianthus annuus L.

Forces applied to plants will subject many of the roots to tension, which must be transferred to the soil via shear if uprooting is to be prevented. The stress distribution will depend on the relative stiffnesses of the earth and root, and the mode of failure will depend on the relative strength of the soil and of the root soil bond. This study of the anchorage of sunflower radicles combined uprooting tests performed by a tensile testing machine with mechanical tests on the roots and soil.
The maximum extraction force increased with length to an asymptotic value and was reached at a very low displacement. Root hairs and soil particles covered the tapered top 20 mm of extracted root, but the lower cylindrical region was bare. The soil was stiffer than the root, so shear stress was initially concentrated at the top of the root, soil strength over the top 20 mm resisting uprooting. Lower regions of the root were stressed later, their sparser root hairs being sheared off, and resist uprooting only by friction. In a further lest upper and lower regions of radicles were uprooted separately. As predicted, the upper region generated much greater resistance to uprooting per unit length, and at much lower displacements than the lower region.
The top of the radicle is well adapted for anchorage, the profuse root hairs and mucigel it produces glueing the root to the soil. The lower regions are thus protected from damage.     

Seed bank dynamics of an invasive alien species,Helianthus annuus L.

形成持久种子库的能力是预测物种在新区域成功建群的最佳指标之一。野生向日葵(Helianthus annuus L.)原产于北美,干扰促进了其种子库的形成,并对本地种群的建立和延续起着关键作用。然而,种子库在入侵种群的建立和延续中所起的作用尚不清楚。在本研究中,我们评估了种子库和干扰对几种向日葵生物类型(采集于阿根廷荒地生境中的野生向日葵、野生农田野生向日葵与作物向日葵自然杂交种,以及商业品种的后代)的建立和适应性,以及土壤中种子持久性的作用。在种子库试验中,我们评估了上述材料两年在干扰和未干扰条件下的出苗率、成活率到繁殖率、出苗成活率、每株花序数和每块地的花序数;在种子埋藏试验中,我们评估了其种子在四个春季(6个月、18 个月、30个月和42个月)土壤中的持久性。研究结果表明,总体而言,幼苗在生长期(冬季)出苗较早,且受到干扰促进,尤其是第一年。尽管如此,在两种情况下,每块样地的花序数是相近的,尤其是荒地生境中。第二年,种子库出苗率较低,但成活率较高。在种子掩埋实验中,观察到遗传差异,荒地和野生生境中种子持久性达到42个月,而商业品种后代的种子持久性不超过6个月。在这两项实验中,农田野生型和商业向日葵品种后代生物型表现出一种中间行为。结果表明,野生向日葵和作物野生向日葵杂交种均能在其生长范围之外形成持久的种子库,且干扰可能有助于其在新区域的建立。     

Redox-related peroxidative responses evoked by methyl-jasmonate in axenically cultured aeroponic sunflower (Helianthus annuus L.) seedling roots

Methyl-jasmonate (MeJA) has been proposed to be involved in the evocation of defense reactions, as the oxidative burst in plants, substituting the elicitors or enhancing their effect. 48 h dark- and sterilely cultured (axenic) aeroponic sunflower seedling roots excised and treated with different concentrations of MeJA showed a strong and quick depression of the H(+) efflux rate, 1.80 microM MeJA totally stopping it for approximately 90 min and then reinitiating it again at a lower rate than controls. These results were wholly similar to those obtained with nonsterilely cultured roots and have been interpreted as mainly based on H(+) consumption for O(2)(*-) dismutation to H(2)O(2). Also K(+) influx was strongly depressed by MeJA, even transitorily reverting to K(+) efflux. These results were consistent with those associated to the oxidative burst in plants. MeJA induced massive H(2)O(2) accumulation in the middle lamella and intercellular spaces of both the root cap cells and the inside tissues of the roots. The native acidic extracellular peroxidase activity of the intact (nonexcised) seedling roots showed a sudden enhancement (by about 52%) after 5 min of MeJA addition, maintained for approximately 15 min and then decaying again to control rates. O(2) uptake by roots gave similar results. These and other results for additions of H(2)O(2) or horseradish peroxidase, diphenylene iodonium, and sodium diethyldithiocarbamate trihydrate to the reaction mixture with roots were all consistent with the hypothesis that MeJA induced an oxidative burst, with the generation of H(2)O(2) being necessary for peroxidase activity. Results with peroxidase activity of the apoplastic fluid were in accordance with those of the whole root. Finally, MeJA enhanced NADH oxidation and inhibited hexacyanoferrate(III) reduction by axenic roots, and diphenylene iodonium cancelled out these effects. Redox activities by CN(-)- preincubated roots were also studied. All these results are consistent with the hypothesis that MeJA enhanced the NAD(P)H oxidase of a redox chain linked to the oxidative burst, so enhancing the generation of O(2)(*-) and H(2)O(2), O(2) uptake, and peroxidase activity by roots.     

Redox-related peroxidative responses evoked by methyl-jasmonate in axenically cultured aeroponic sunflower (Helianthus annuus L.) seedling roots

Summary.  Methyl-jasmonate (MeJA) has been proposed to be involved in the evocation of defense reactions, as the oxidative burst in plants, substituting the elicitors or enhancing their effect. 48 h dark- and sterilely cultured (axenic) aeroponic sunflower seedling roots excised and treated with different concentrations of MeJA showed a strong and quick depression of the H⁺ efflux rate, 1.80 μM MeJA totally stopping it for approximately 90 min and then reinitiating it again at a lower rate than controls. These results were wholly similar to those obtained with nonsterilely cultured roots and have been interpreted as mainly based on H⁺ consumption for O₂ ^•− dismutation to H₂O₂. Also K⁺ influx was strongly depressed by MeJA, even transitorily reverting to K⁺ efflux. These results were consistent with those associated to the oxidative burst in plants. MeJA induced massive H₂O₂ accumulation in the middle lamella and intercellular spaces of both the root cap cells and the inside tissues of the roots. The native acidic extracellular peroxidase activity of the intact (nonexcised) seedling roots showed a sudden enhancement (by about 52%) after 5 min of MeJA addition, maintained for approximately 15 min and then decaying again to control rates. O₂ uptake by roots gave similar results. These and other results for additions of H₂O₂ or horseradish peroxidase, diphenylene iodonium, and sodium diethyldithiocarbamate trihydrate to the reaction mixture with roots were all consistent with the hypothesis that MeJA induced an oxidative burst, with the generation of H₂O₂ being necessary for peroxidase activity. Results with peroxidase activity of the apoplastic fluid were in accordance with those of the whole root. Finally, MeJA enhanced NADH oxidation and inhibited hexacyanoferrate(III) reduction by axenic roots, and diphenylene iodonium cancelled out these effects. Redox activities by CN⁻- preincubated roots were also studied. All these results are consistent with the hypothesis that MeJA enhanced the NAD(P)H oxidase of a redox chain linked to the oxidative burst, so enhancing the generation of O₂ ^•− and H₂O₂, O₂ uptake, and peroxidase activity by roots. Received July 12, 2002; accepted October 2, 2002; published online May 21, 2003 RID="*"     

Shade-Induced Action Potentials in Helianthus annuus L. Originate Primarily from the Epicotyl

Repeated observations that shading (a drastic reduction in illumination rate) increased the generation of spikes (rapidly reversed depolarizations) in leaves and stems of many cucumber and sunflower plants suggests a phenomenon widespread among plant organs and species. Although shaded leaves occasionally generate spikes and have been suggested to trigger systemic action potentials (APs) in sunflower stems, we never found leaf-generated spikes to propagate out of the leaf and into the stem. On the contrary, our data consistently implicate the epicotyl as the location where most spikes and APs (propagating spikes) originate. Microelectrode studies of light and shading responses in mesophyll cells of leaf strips and in epidermis/cortex cells of epicotyl segments confirm this conclusion and show that spike induction is not confined to intact plants. 90% of the epicotyl-generated APs undergo basipetal propagation to the lower epicotyl, hypocotyl and root. They propagate with an average rate of 2 ± 0.3 mm s⁻¹ and always undergo a large decrement from the hypocotyl to the root. The few epicotyl-derived APs that can be tracked to leaf blades (< 10%) undergo either a large decrement or fail to be transmitted at all. Occasionally (5% of the observations) spikes were be generated in hypocotyl and lower epicotyl that moved towards the upper epicotyl unaltered, decremented, or amplified. This study confirms that plant APs arise to natural, nontraumatic changes. In simultaneous recordings with epicotyl growth, AP generation was found to parallel the acceleration of stem growth under shade. The possible relatedness of both processes must be further investigated.Key Words: Helianthus annuus L., action potentials, natural induction, AP propaqgation, amplification, stem growth, decrement     

Systemic acquired resistance in sunflower (Helianthus annuus L.)

Systemic acquired resistance (SAR) to infection by Botrytis cinerea in the leaves of sunflower (Helianthus annuus L.) plants was induced following cotyledon inoculation with B. cinerea or treatment with abiotic inducers. Salicylic acid (SA), benzo-(1,2,3)-thiadiazole-7-carbothioic S-methyl ester (BTH), 2,6-dichloroisonicotinic acid (INA) or EDTA protected sunflower plants against Botrytis infection, that was revealed by a reduction in the number and area of the necrotic lesions in upper leaves after challenge inoculation with the pathogen. SA and BTH were more potent inducers than INA, EDTA or pre-inoculation with the fungus. In addition to resistance to B. cinerea, the upper leaves have also developed resistance to maceration by a mixture of cell wall-degrading enzymes. Calcium nitrate inhibited both the protective effect and the resistance of leaf discs to cell-wall degrading enzymes. All the tested chemicals increased the synthesis and excretion of sunflower phytoalexins--coumarins scopoletin and ayapin and induced the PR-proteins chitinase and 1,3-beta-glucanase, being the inducer effect of each activator correlated with the level of protection against B. cinerea (BTH > SA > INA > EDTA). Thus, SAR induction is mediated by general increase of plant defence responses. This is the first report on SAR in sunflower.     

Nuclear DNA changes within Helianthus annuus L.: origin and control mechanism

Summary Previous results suggested that the amount of nuclear DNA varies in one and the same progeny of Helianthus annuus, depending on the head portion in which seeds have developed. Accordingly, cytophotometric determinations were carried out in a selfed line, after Feulgen-staining, to obtain information on the developmental stages at which DNA changes are produced and on the mechanism controlling the variation. It was found that the Feulgen absorption values of mitotic prophases in immature anthers and pistils and of meiotic prophases I are the same in any flower of the head. In contrast, the Feulgen/DNA contents of early prophases in heart-shaped embryos differ significantly, increasing from those developing at the centre of the head to those developing at its periphery, and remaining unchanged in each embryo during further development and seed germination. Variations in the number of chromosomes do not account for the differences observed in nuclear DNA contents in which sequences comprised in heterochromatic nuclear regions are involved. The Feulgen absorption values of seedlings obtained from seeds developed in different portions of single heads increase or diminish starting from those found in the mother plant. This depends on whether these latter are relatively low or high and on the gradient of seed location in the head. The variation occurring within each single progeny covers the whole range existing within the line.