Control of Adventitious Root Production and Hypocotyl Hypertrophy of Sunflower (Helianthus annuus) in Response to Flooding

Needles of 20-year-old Scots pine trees (Pinus silvestris L.) were permitted to photoassimilate ¹⁴CO₂ for 1 h on different dates during the growing season. The loss of radioactivity from current, 1-year-old, and 2-year-old needles was followed, and the translocation of photoassimilated ¹⁴CO₂ from older needle age-classes to the elongating new needles studied. The effects of good mineral and water supply on translocation were also considered. In the spring, 1-year-old and 2-year-old needles accumulated ¹⁴C. These reserves, together with current photosynthate, were utilized when the trees started growing. The 1-year-old needles exported ¹⁴C to the current needles during the first weeks of elongation of the later, while no such translocation occurred from the 2-year-old needles. Removal of the 1-year-old needles resulted in translocation of assimilates from the 2-year-old needles to the current needles. The general pattern of translocation observed in the control trees was not changed when the trees were fertilized and irrigated. The new needles started to export assimilates in the middle of July when the photosynthetic rate per needle was comparable with that of the older age-classes. This occurred about 4 weeks after positive net photosynthesis was first measured for the current shoot. The current needles of trees with good nutrient and water supply seemed to become self-sufficient in photoassimilates earlier than the current needles of the control trees.     

Effects of Mineral Nutrition on Endogenous Cytokinins in Plants of Sunflower (Helianthus annuus L.)

The effects of inorganic nutrients on the levels of endogenouscytokinins in plants of sunflower (Helianthus annuusL.) grownin sand culture were studied. Low levels of nitrogen resultedin rapid decreases in the levels of cytokinins extracted fromleaves, buds, roots, and root exudates. Similar effects wereobserved with phosphorus deficiency, but the effects of potassiumdeficiency on the cytokinin content of leaves was less marked.The cytokinin content was higher in plants supplied with nitrogenas nitrate than in those supplied with ammonium sulphate orammonium nitrate. The decline in cytokinin levels in derooted shoots and detachedleaves could be reversed by supplying them with nutrient solution.Although leaves on intact plants may normally be dependent uponthe supply of cytokinins from the roots, isolated leaves havethe capacity for cytokinin production when supplied with inorganicnutrients.     

Effect of Mechanical Stress on Sunflower (Helianthus annuus L.) Hypocotyl Growth

Etiolated seedlings of Sunflower (Helianthus annuus L.) weresubjected to mechanical stress by longitudinally compressingthe hypocotyl with approx. 0·05 N force (equivalent to0·025 MPa for a 1·6 mm diameter hypocotyl). Thisrelatively low compressive stress effected an increase in relativegrowth rates (RGR) of the hypocotyl for a period of 1-2 h, followingwhich RGR returned to the pretreatment rate. RGR was also increasedby an equivalent compressive stress treatment (0·025MPa) for 4 h in water or in 10^-10 mol l^-1 IAA. These resultsare discussed in the context of a possible role for mechanicallyinduced stress in the initiation and maintenance of nutationalgrowth movements.Copyright 1994, 1999 Academic Press Helianthus annuus, Sunflower, hypocotyl growth, mechanical stress, seedling growth, nutational growth movements, circumnutation     

Role of Mechanical Loading in Growth of Sunflower (Helianthus annuus) Seedlings

Seedlings of the herbaceous annual Helianthus annuus L. weregrown under three regimens of daily bending. Bending wasadjustedduring ontogeny so that the deflexion of the stem tip dividedby the stem height was constant (elastic similarity). After6weeks, mechanically–treated plants exhibited a significantlygreater ratio of stem diameter to stem height, flexural stiffness,stemgrowth rate, and proportion of collenchymatous tissue inthe stem. Treated plants were also significantly smaller inheight,showed a greater proportion of stem tissue as cortex,and greater initial stem growth rate. No significant differenceswereobserved in the elastic modulus of the tissue composingthe stem, above–ground biomass, and stem diameter. Thedegree ofmechanical loading also had a significant effect onmost parameters. The most highly stressed plants were thicker,shorter, and elastically stiffer with more collenchyma and lesscortex in the stem. Since plants were loaded for only 60 s d^–1it is concludedthat mechanical effects early in life can haveprofound effects on the form and hence ecology of seedlings. Key words: Seedling growth, Helianthus annuus L., stem mechanical properties, thigmomorphogenesis, bending stress     

Adventitious rooting in hypocotyls of sunflower (Helianthus annuus) seedlings

Removal of the main root system of sunflower ( Helianthus annuus ) initiates adventitious root development on the lower portion of the hypocotyl. The first cytological changes (enlarged nuclei in the interfascicular parenchymatous cells adjacent to the phloem and some cell divisions) are observed 24 h after root excision. On the basis of experiments in which (a) roots, apical buds and various amounts of cotyledonary tissue were removed, (b) cuttings were subjected to various light regimes, (c) benzyladenine oas applied to cotyledons to create an artificial sink, it was concluded that the roots normally produce factors inhibiting to adventitious rooting and might be a sink for stimulatory substances produced in the shoots. The cotyledons seem to be the major source of these stimulators. Application of aqueous and ethanolic extracts of cotyledons and hypocotyls to cuttings promoted adventitious rooting.     

Membrane-bound Plastid Inclusions and Chloroplast Thylakoid Formation in Sunflower (Helianthus annuus L.)

The ultrastructure, distribution and frequency of membrane-boundplastid inclusions present in the epidermal cells of leavesof intact sunflower plants (Helianthus annuus L.) and in theepidermal and mesophyll cells of sunflower leaf discs culturedin darkness have been studied. These inclusions appear to bedilated thylakoids containing a granular material which, undernormal conditions, is probably involved in chloroplast membraneformation. It is suggested that this material accumulates, andinclusions form, in the chloroplasts of sunflower leaves intwo specific situations. Firstly, in the completely differentiatedcells of the epidermis where the chloroplasts, although at arelatively immature stage, have nevertheless reached a terminalstage of development. Secondly, in the mesophyll cells of youngleaves when chloroplast development has been arrested at animmature stage by a 5-day dark period. In the latter situationthe material can be remobilized if plastid development is restimulated.The plastids of sunflower leaf discs cultured in darkness containboth membrane-bound inclusions and prolamellar bodies, indicatingthat they are separate and distinct structures possibly containingdifferent membrane components. Helianthus annuus L., sunflower, chloroplast, ultrastructure, plastid inclusions, thylakoid formation     

The Nature and Location of Variable Hydraulic Resistance in Helianthus annuus L. (Sunflower)

Koide, R. 1985. The nature and location of variable hydraulicresistance in Helianthus annuus L. (sunflower).—J. exp.Bot. 36: 1430–1440. Hydraulic resistances for whole sunflower plants (Helianthusannuus L.) and sunflower leaves, stems, petioles and roots weremeasured. Whole plant hydraulic resistance was shown to declinewith an increase in transpiration. Leaf hydraulic resistancewas shown, with one technique employing transpiring leaves,to vary with transpiration and with another technique, employingpressure-induced flow in leaves, to be constant over a widerange of transpiration. Stem and petiole hydraulic resistanceswere constant over a wide range of exudation. Pressure-inducedflow through root systems was shown to be an inappropriate methodfor characterizing their hydraulic properties because flow mayoccur through unnatural paths. The technique employing measuredtranspiration rates and water potentials of non-growing leavesand soil is suggested to be better. The evidence presented inthis study suggests that the hydraulic resistance of the transpirationstream does vary and that the site of variability is the root Key words: Hydraulic resistance, sunflower, pressure-induced water flow     

Inter-organ Synergism and the Control of Chlorophyll Accumulation in Sunflower (Helianthus annuus) Cotyledons

Prior to illumination, the embryonic axis of sunflower seedlingsmakes a contribution to the cotyledons which enables them togreen more rapidly when subsequently irradiated with white light.The contributions made to this stimulation by the hypocotylhook, hypocotyl, and roots have been investigated. Greeningin sunflower cotyledons reaches an optimum rate when they are6 d old. The developing embryonic axis not only promotes theattainment of this optimum rate but also aids in the maintenanceof this optimum rate as the cotyledons continue to age. Thisstimulatory effect appears to arise primarily from the rootsand can be duplicated by the exogenous application of benzyladenine. In contrast to previous reports we find that the hypocotyl hookplays no role in the control of greening when present duringillumination.     

Water Relations of Sunflower (Helianthus annuus) Shoots during Exposure of the Root

The influence of root anoxia on the water balance of hydroponicallygrown sunflower plants was investigated in a controlled environmentroom. Leaf water potentials declined within 1 h of the onsetof anaerobic treatment of the roots. The severity of the waterstress during the initial 8 h of treatment was dependent onthe ambient humidity of the aerial environment. Recovery ofshoot water balance occurred by the beginning of the secondfull day of treatment, without stomatal closure. After 3 d of continuous anaerobic treatment, plant responsein the same experiment followed one of two patterns. In thefirst, there were declines in leaf water content, leaf waterpotentials, lamina expansion, transpiration rates and stomatalconductance. Osmotic adjustment occurred but it was not sufficientto prevent loss of turgor and the plants wilted at day 4 oftreatment. Complete rehydration took place after 6 d of treatmentif the stem was severed (under water) just below the cotyledons,indicating that shoot dehydration was a result of xylem occlusionat the root/shoot interface. Sections of the stem in this regionshowed xylem vessels to be discoloured and plate-like structuresobstructing the lumen. In the other pattern of response, plants did not develop a morenegative leaf water potential (except for an initial periodimmediately following treatment initiation) throughout the 6-danaerobic treatment period. There were no signs of water deficitalthough other symptoms such as precocious leaf senescence andepinasty occurred concomitantly with those in the first groupof plants that developed long-term water stress. Changes in shoot water relations are discussed in terms of ourearlier observations on anoxia-induced changes in the hydraulicconductivity and selectivity of the roots. Possible explanationsare offered for inter-plant variations in response to root anoxia. Key words: Anaerobiosis, water relations, xylem blockage     

Hormonal Regulation of Phototropism in the Light-grown Sunflower Seedling, Helianthus annuus L.: Immobility of Endogenous Indoleacetic Acid and Inhibition of Hypocotyl Growth by Illuminated Cotyledons

Light-grown sunflower seedlings contain 10^–7–3 x10^–7 M indoleacetic acid (IAA). The even distributionof this endogenous IAA in straight hypocotyls does not changeduring phototropic curvature. The diffusate from hypocotylscontains substance(s) influencing the elongation rate of Avenacoleoptile segments but hardly any IAA. Phototropic curvature of the hypocotyl requires the presenceof illuminated cotyledons. Illumination of cotyledons inhibitshypocotyl growth. It is concluded that the phototropic response of the sunflowerhypocotyl is regulated by factors promoting and inhibiting cellelongation other than IAA.     

l-Arginine Pretreatment Enhances Drought Resistance of Sunflower (Helianthus annuus L.) Plants by Increase in Polyamines Content

Journal of Plant Growth Regulation - A significant reduction of fresh, dry biomass, shoot height, root length, succulent value, and leaf area were noticed as well as a significant accumulation of...     

不同氮素形态对向日葵生长和光合功能的影响

利用砂培试验研究了不同氮素形态对向日葵生长和光合功能的影响。结果表明：NO^3-N(NN)处理的株高、叶面积、干物质重显著高于NH4^ -N(AA)处理,施用NO3^--N的植株有较高的净光合速率(Pn)和较低的气孔导度(C8)、细胞间隙CO2浓度(Ci)。不同处理之间Fv／Fm没有显著差异,NN处理的植株PSⅡ线性电子传递量子效率ФPSⅡ、光化学荧光猝灭系数qP和表观光合电子传递效率ETR都显著高于AA处理的植株;而非光化学荧光猝灭系数qN则明显低于AA处理的植株。碳同化受到抑制是NH4^ -N条件下净光合速率下降的重要原因。     

Adventitious rooting in hypocotyls of sunflower (Helianthus annuus) seedlings. III. The role of ethylene

While ethylene is suspected to be one of the many factors that play a role in rooting, some studies have found that ethylene can promote rooting, while others show it to inhibit this process or to have no effect. Using seedlings of sunflower ( Helianthus annuus L. cv. Dahlgren 131) we carried out observations on the rates of ethylene production and the levels of the ethylene precursor, 1-aminocyclopropane-l-car-boxylic acid (ACC), and ACC conjugate, l-(malonylamino)cyclopropane-l-car-boxylic acid (MACC), during the process of root initiation. The changes in these substances in the base of the hypocotyls (the portion that produces roots) were compared to the changes that occurred in the top of the hypocotyls (non-rooting portion). We also supplied a number of presumptive inhibitors of ethylene biosynthesis and inhibitors of ethylene action for short periods during the early and critical stages of root formation. Their effects on ethylene action, synthesis and rooting were examined. We conclude that the wound-induced increase in ethylene, seen within 3 h of production of the cuttings, is a key stimulatory factor in the formation of root primordia. When this increase in ethylene is localized in the lower portion of the hypocotyl, there is a promotion of rooting. On the other hand, higher concentrations in the top of the hypocotyls (as compared to the bottom) may inhibit rooting.     

The Micronutrient Boron Causes the Development of Adventitious Roots in Sunflower Cuttings

Three-day-old light-grown sunflower seedlings were de-rootedand incubated in nutrient solutions that either contained orlacked boric acid (B). In the absence of B, in the majorityof the seedlings, no adventitious roots were formed. The micronutrientB caused the development of numerous roots in the lower partof the hypocotyl. The effect of B occurred without the supplyof any phytohormones. A dose-response curve of B-induced rootingyielded an optimum concentration of 0.1 mM boric acid. Histologicalstudies revealed that cell divisions occurred in the controlbut no root primordia developed. In cuttings that were incubatedin B (0.1 m M) root primordia were observed that rapidly developedinto well-differentiated adventitious roots. Sunflower cuttingsthat were planted with their cut end in vermiculite that wasmoistened with nutrient solutions without B degenerated afterseveral weeks. In the presence of B the cuttings formed numerousadventitious roots that entirely replaced the tap root systemof intact seedlings. The rooted cuttings developed into sturdyadult sunflower plants. Our results are discussed with respectto the possible role of B in the evolution of vascular fromprevascular plants.Copyright 1999 Annals of Botany Company Adventitious roots, boron, cuttings, organogenesis, sunflower seedlings.     

Effect of Potassium Supply on the Acropetal Transport of Water, Inorganic Ions and Amino Acids in Young Decapitated Sunflower Plants (Helianthus annuus)

The effect of potassium supply on the exudation rate and the content of ions and amino acids in exudation sap was studied using young decapitated sunflower plants (Helianthus annuus L.). Plants were grown originally in a complete nutrient solution. After decapitation one set of plants was transferred to a nutrient solution without potassium and another set to a solution with potassium, all other nutrients remaining the same for both treatments. During an experimental period of 3 days the plants supplied with potassium showed exudation rates which were more than twice as high as plants in the nutrient medium without potassium. The potassium supply affected the potassium and nitrate contents of the exudation sap. Both were lower in the treatment without potassium. The calcium and magnesium contents of the exudation sap were not significantly influenced by the potassium treatment, whereas the phosphate content was higher in the treatment without potassium. At the beginning of the exudation period the potassium supply did not affect the content of amino acids in the exudate, but later the plants supplied with potassium showed higher contents of amino acids in the exudation sap. As the absence of potassium reduced the exudation rate considerably the acropetal transport of all exudation sap constituents analysed in this experiment was markedly reduced.     

Sunflower (Helianthus annuus L.) Pathogenesis-Related Proteins (Induction by Aspirin (Acetylsalicylic Acid) and Characterization)

Sunflower leaf discs floated on a solution containing aspirin (acetylsalicylic acid) produced a set of new proteins extractable at pH 5.2 and excreted into the intercellular space. More than 80% of the proteins found in the intercellular fluids of induced leaf discs have been identified as pathogenesis-related (PR) proteins by their immunological relationship with tobacco PR proteins. Members of the four major classes of PR proteins have been characterized. Sunflower PR proteins of type 1 (PR1) and of type 3 (PR3) were found to have acidic isoelectric points, whereas the induced PR protein of type 2 (PR2) had a basic isoelectric point. Members of the type 5 PR proteins (PR5), known in tobacco as thaumatin-like proteins, showed a more complex pattern. Multiple sunflower PR5 isomers of similar molecular weight but of different isoelectric points were excreted from the cells in response to the aspirin treatment. PR2 and PR3 proteins were found at very low basal levels in untreated leaves, whereas PR1 and PR5 proteins could not be detected at all in the same extracts. Glucanase and chitinase activities were always associated with PR2 and PR3 proteins in partially purified sunflower extracts. All of these data indicate that, in response to aspirin treatment, sunflower plants produce a complete set of PR proteins characterized by an apparently exclusively extracellular localization.     

Selection on Crop-Derived Traits and QTL in Sunflower (Helianthus annuus) Crop-Wild Hybrids under Water Stress

Locally relevant conditions, such as water stress in irrigated agricultural regions, should be considered when assessing the risk of crop allele introgression into wild populations following hybridization. Although research in cultivars has suggested that domestication traits may reduce fecundity under water stress as compared to wild-like phenotypes, this has not been investigated in crop-wild hybrids. In this study, we examine phenotypic selection acting on, as well as the genetic architecture of vegetative, reproductive, and physiological characteristics in an experimental population of sunflower crop-wild hybrids grown under wild-like low water conditions. Crop-derived petiole length and head diameter were favored in low and control water environments. The direction of selection differed between environments for leaf size and leaf pressure potential. Interestingly, the additive effect of the crop-derived allele was in the direction favored by selection for approximately half the QTL detected in the low water environment. Selection favoring crop-derived traits and alleles in the low water environment suggests that a subset of these alleles would be likely to spread into wild populations under water stress. Furthermore, differences in selection between environments support the view that risk assessments should be conducted under multiple locally relevant conditions.     

ABA in Roots and Leaves of Flooded Pea Plants

Zhang, J. and Davies, W. J. 1987. ABA in roots and leaves offlooded pea plants.—J. exp. Bot. 38: 649–659. Roots of potted pea (Pisum sativum L. cv. Feltham First) seedlingswere flooded with tap water. Within a few hours of the startof the flooding treatment the content of free ABA in roots increasedcompared to contents of roots of unflooded control plants butthis increase was not statistically significant until the beginningof the second day after flooding. Approximately 36 h after firstflooding significant increases in the free-ABA content of leaveswere detected. This was 14 h after significant increases inthe amount of ABA in the roots of the same plants. There wasmarked diurnal variation in free-ABA content of leaves and rootsof plants that had been flooded for several days, with maximumcontents recorded 3 h or more after the beginning of the lightperiod. Very rapidly after the lights were switched oft ABAcontents declined. On day 3 of the flooding treatment, therewas more than a 5-fold decrease in the free-ABA content of leaveswithin a few hours of the beginning of the dark period. Radio-immunoassaysuggested that a very large proportion of the total ABA in theplant was in a bound form. This form of ABA increased substantiallyas the flooding period progressed. The importance of variation in ABA content for the control ofwater relations and gas exchange of flooded plants is discussed. Key words: Flooding, Pisum sativum, ABA, water relations     

油用向日葵主要农艺性状的遗传分析

对10个油用向日葵品种的主要农艺性状进行遗传分析的结果表明,株高、单株粒数、百粒重、盘径和单株粒重等农艺性状具有较大的遗传率,可以在早代单株选择或直接选择;出苗-现蕾、现蕾-开花、开花-成熟、皮壳率等性状的遗传率较低,应根据各性状间相关关系进行间接选择或将选择推迟到晚期世代进行。遗传变异幅度较大的性状有皮壳率、单株粒数、小区产量、单株粒重等。由于性状的遗传改良效果主要由该性状的遗传率和变异幅度及选择强度所决定,因此,在选择率确定为5%情况下,遗传改良效果较好的性状为单株粒数和单株粒重。 Abstract:The genetic analysis of main agronomic characters was conducted with 10 varieties of oil sunflower(Helianthus annuus L.).The results showed that direct selection can be carried out at early generation for characters with higher heritability such as plant height,grain number pere plant,100-grain weight,diameter of disc and grain weight per plant.For maturity and percentage of shell with lower heritability,indirect selection correlated with other characters or late generation selection can be utilized.The characters showing wide genetic variation were those as percentage of shell,grain number per plant,grain yield per plot and grain weight.Since the successful improvement of a character mainly depends on its heritability,variation of heritability and intensity of selection,we suggest that the characters which may give better genetic improvement are grain number and grain weight per plant under condition of 5% selection pressure.