Responses of the Root Systems of Sunflower and Maize to Unidirectional Stem Flexure

Plants of two contrasting species of herbaceous annuals, thedicot sunflower (Helianthus annuusL.) and the monocot maize(Zea maysL.), grown in the glasshouse were subjected to regularunidirectional stem flexure. Differences in morphology and mechanicalproperties of roots and shoots were then investigated. Rootsystems were divided into quadrants around the axis of stimulationand differences in root morphology and mechanics between thezones were investigated. There were considerable differencesbetween roots in the leeward and windward zones compared withroots perpendicular to the axis of stimulation. First-orderlateral roots in both species were thicker, more rigid and morenumerous. These results suggest that plant roots respond locallyto mechanical stimulation. There were, however, also differencesin the responses of the two species. In sunflower, the tap rootand stem base became elliptical in cross section with the majoraxis lying in the plane of stimulation. The lateral roots offlexed sunflowers in both the leeward and windward zones showedsimilar growth responses: roots were thicker, more numerousand weighed more than those in the perpendicular zones. However,only leeward roots showed significant differences in their mechanicalproperties; roots were more rigid, stronger and stiffer. Incontrast, the leeward roots of maize were thicker and more numerous,with a greater biomass than the windward roots. However, onlyroots in the windward zone were stiffer than those in the perpendicularzone. These differences between sunflower and maize are relatedto their contrasting anchorage mechanics.Copyright 1998 Annalsof Botany Company Anchorage, biomechanics, adaptive growth, roots, thigmomorphogenesis,Helianthus annuusL.,Zea maysL.     

A comparative study of the response of the roots and shoots of sunflower and maize to mechanical stimulation

Despite numerous studies of the effects of mechanical stimulationon plant shoots, the response of roots to mechanical stimulationhas largely been neglected. In this study the effects of shootflexure on the morphology and mechanics of two contrasting speciesof herbaceous angiosperm, growing in a glasshouse were compared:maize (Zea mays), a monocot; and sunflower (Helianthus annuusL.) a dicot. Mechanical stimulation affected the root more than the shootcomponents. Root systems of mechanicallystressed sunflowershad a greater angle of spread and increased root number. Aswell as large morphological and weight effects, with increasesover the control of 33% in the length of rigid root and 38%in the dry weight of lateral roots, in sunflowers, there werealso mechanical effects. In both species roots of flexed plantswere more rigid, stronger and composed of stiffer material andtheir root systems also provided greater anchorage strength.In contrast, there was only a small reduction in shoot weightand shoot height in flexed plants and no effects on mechanicalproperties. There were differences in behaviour between species; maize rootmorphology responded less than that of sunflowers to mechanicalstimulation. The basal diameter of roots increased by only 8%compared with 16% in sunflowers, though the roots of both speciesshowed similar increases in material stiffness. This differenceis related to the lack of secondary thickening in the monocotscompared with the dicot sunflowers. Key words: Thigmomorphogenesis, Helianthus annuus L., Zea mays, anchorage, lodging     

Does ABA in the Xylem Control the Rate of Leaf Growth in Soil-Dried Maize and Sunflower Plants?

Maize (Zea mays L.) and sunflower (Helianthus annuus L.) plantswere grown in large volumes of soil and leaf growth rate wasmonitored on a daily basis. Half the plants were given a soildrying treatment and when they showed a significant restrictionof growth rate (compared to both their daily growth rate beforedrying and the average growth rate of well-watered plants onthe same day), leaf water relations were measured and xylemsap was extracted using several techniques. There was a significant negative log-linear relationship betweenthe rate of leaf growth and the concentration of ABA in thexylem for both species. There was no clear relationship betweenleaf growth rate and leaf water potential or turgor for eitherspecies. Assessment of different methods for sampling xylemsap suggests that exudates collected from stem stumps or samplescollected by pressurizing the whole root system are suitablefor estimating ABA concentration in xylem, at least with largeplants of maize or sunflower, provided the first few hundredcubic millimetres of collected sap are used for the assay. Centrifugationof sections of stems resulted in dilution of ABA in the xylemsap with sap squeezed from parenchyma tissue. This is because,at least in plants subjected to mild soil drying, the concentrationof the ABA in the xylem is far higher than that in the cellsap of stem tissue. Results support the proposal that ABA plays a major role asa chemical signal involved in the root-to-shoot communicationof the effects of soil drying. The non-hydraulic restrictionof leaf growth by a chemical signal can be explained by theextra root-sourced ABA in the xylem and may be an importantcomponent of the modification of growth and development whichresults from prolonged soil drought. Key words: Soil drying, ABA, leaf growth, Zea mays L., Helianthus annuus L.     

Profiles of Leaf Senescence During Reproductive Growth of Sunflower and Maize

We investigated the effect of reproductive growth on the profilesof leaf senescence in maize (Zea mays L.) and sunflower (Helianthusannuus L.). Leaf senescence after flowering was assessed usingboth structural (leaf chlorophyll, nitrogen and dry matter)and functional (photosynthesis) variables in undisturbed plants(+G) and in plants in which grain set was prevented (-G). Twoweeks after flowering, lack of grain accelerated senescencein maize and delayed senescence in sunflower as indicated byleaf chlorophyll; leaf nitrogen and dry matter were less sensitiveresponse variables. Lack of interaction between reproductivetreatment and leaf position indicates that the senescence signal,whatever its nature, was equally effective throughout the plantin both species. In both species, feedback inhibition of photosynthesiswas first detected 30–35 d after flowering; excess carbohydratein the leaves was therefore an unlikely trigger of acceleratedsenescence in maize. As reproductive development progressed,differences between +G and -G plants were more marked in sunflower,and tended to disappear or reverse in maize. In sunflower, interactionsbetween leaf position and reproductive treatment—attributableto the local effect of grain—were detected around 20–27d after flowering. Copyright 2000 Annals of Botany Company Helianthus annuus, Zea mays, chlorophyll, light, nitrogen, photosynthesis, reproductive growth, senescence, source-sink, SPAD.     

Male Sterility and Anther Wall Structure in Copper-deficient Plants

Anther development and pollen sterility were followed in plantsof wheat, oat, barley, sweetcorn, sunflower, petunia and subterraneumclover grown at a range of copper supplies. Copper-deficientplants had increased pollen sterility. Lignified wall thickenings were reduced or absent in the endotheciaof anthers from Cu-deficient plants. Reduced seed set may resultboth from reduced pollen fertility or failure of the stomiato rupture due to decreased lignification of anther walls. Triticum aestivum L., wheat, Hordeum vulgare L., barley, Avena sativa L., oat, Zea mays L., corn, sweetcorn, maize, Helianthus annuus L., sunflower, Petunia hybrida L., Trifolium subterraneum L., subterranean clover, male sterility, anther development, copper deficiency     

The Effects of Soil Bulk Density on the Morphology and Anchorage Mechanics of the Root Systems of Sunflower and Maize

The effects of soil bulk density and hence strength on two contrastingspecies of herbaceous annuals, the dicot sunflower (HelianthusannuusL.) and the monocot maize (Zea maysL.), were investigatedby comparing the morphology and mechanics of field-grown plantsin soil with a low and high bulk density. Soil with a low bulkdensity had a significantly lower penetration resistance (118±4.4kPa) than the high bulk density soil (325±12.2 kPa;P<0.0001).Soil strength affected shoot and root systems of both speciesbut had no significant effect on shoot height. In both speciesroots were thicker closer to the stem base in strong soil comparedto those in weaker soil. Sunflower tap-roots growing in strongsoil tapered more rapidly than those in weak soil. Only in maize,however, were roots growing in weak soil stiffer than thosein strong soil. Despite only small absolute differences in thepenetration resistance of the soil both species growing in strongsoil had greater anchorage strength than those in weak soil.As a consequence more plants in weak soil lodged compared withthose growing in strong soil. This study shows that plants can,to a small extent, respond to changes in soil strength, butthat changes do not appear to compensate fully for alterationsin soil conditions. Furthermore it may be possible, by manipulatingsoil strength, to control lodging.Copyright 1999 Annals of BotanyCompany Roots, compaction, soil strength, anchorage mechanics, bulk density, thigmomorphogenesis, lodging,Helianthus annuusL.,Zea maysL.     

Effects of Water Stress and High-Temperature Stress on the Structure and Activity of Photosynthetic Apparatus of Zea Mays and Helianthus Annuus

Effects of high-temperature stress (HTS) and PEG-induced water stress (WS), applied separately or in combination, on the functional activity and ultrastructure of the photosynthetic apparatus (PSA) of maize (Zea mays L.) and sunflower (Helianthus annuus L.) plants were investigated. In maize plant tissues WS provoked the decrease in RWC by 10.9 %, HTS by 7.0 %, and after simultaneous application of the both treatments the decrease was 32.7 % in comparison with control plants. Similar but more expressed changes were observed in sunflower plants. Sunflower was more sensitive to these stresses. Net photosynthetic rate decreased significantly after all treatments, more in sunflower. In mesophyll chloroplasts after separately applied WS and HTS the number of grana and thylakoids was reduced and electron-transparent spaces appeared. At combined stress (WS+HTS) granal and stromal thylakoids were considerably affected and chloroplast envelope in many of them was partially disrupted. This revised version was published online in August 2006 with corrections to the Cover Date.     

Distribution of Protein-bound Hexosamine in Chloroplasts

Intact chloroplasts of spinach (Spinacia oleracea L.), sunflower (Helianthus annuus L.), and maize (Zea mays L.) mesophyll cells contained 0.33, 0.50, and 0.14% of bound hexosamine on a protein basis, respectively. Undifferentiated maize chloroplasts contained 0.19%. Values for chloroplast lamellae were, respectively, 0.16, 0.18, 0.12, and 0.06% and for envelope membranes they were 1.6, 2.5, 3.8, and 2.7%. Thus most of the hexosamine of chloroplasts is located in the envelope membrane.     

Blue light activates a specific protein kinase in higher plants

Blue light mediates the phosphorylation of a membrane protein in seedlings from several plant species. When crude microsomal membrane proteins from dark-grown pea (Pisum sativum L.), sunflower (Helianthus annuus L.), zucchini (Cucurbita pepo L.), Arabidopsis (Arabidopsis thaliana L.), or tomato (Lycopersicon esculentum L.) stem segments, or from maize (Zea mays L.), barley (Hordeum vulgare L.), oat (Avena sativa L.), wheat (Triticum aestivum L.), or sorghum (Sorghum bicolor L.) coleoptiles are illuminated and incubated in vitro with [γ-³²P]ATP, a protein of apparent molecular mass from 114 to 130 kD is rapidly phosphorylated. Hence, this system is probably ubiquitous in higher plants. Solubilized maize membranes exposed to blue light and added to unirradiated solubilized maize membranes show a higher level of phosphorylation of the light-affected protein than irradiated membrane proteins alone, suggesting that an unirradiated substrate is phosphorylated by a light-activated kinase. This finding is further demonstrated with membrane proteins from two different species, where the phosphorylated proteins are of different sizes and, hence, unambiguously distinguishable on gel electrophoresis. When solubilized membrane proteins from one species are irradiated and added to unirradiated membrane proteins from another species, the unirradiated protein becomes phosphorylated. These experiments indicate that the irradiated fraction can store the light signal for subsequent phosphorylation in the dark. They also support the hypothesis that light activates a specific kinase and that the systems share a close functional homology among different higher plants.     

Lipid and Fatty Acid composition of chloroplast envelope membranes from species with differing net photosynthesis

Lipid and fatty acid compositions were determined for chloroplast envelope membranes isolated from spinach (Spinacia oleracea L.), sunflower (Helianthus annuus L.), and maize (Zea mays L.) leaves. The lipid composition was similar in sunflower, spinach, and undifferentiated maize chloroplast envelope membranes and different in maize mesophyll chloroplast envelope membranes. The predominant lipid constituents in all envelope membranes were monogalactosyldiglyceride (27 to 46%), digalactosyldiglyceride (18 to 33%), and phosphatidylcholine (7 to 30%). The fatty acid composition was also similar in sunflower and spinach chloroplast envelope membranes in comparison to those from maize. The major acyl fatty acids of the chloroplast envelope membrane were palmitic (C_16:0, 41 and 36%) and linolenic (C_18:3, 29 and 40%) acids for spinach and sunflower; palmitic (77%) and stearic (C_18:0, 12%) acids for young maize; and palmitic (61%), stearic (14%), and linolenic (13%) acids for mature maize. The differences in lipid and acyl fatty acid compositions among these plants which vary in their rates of net photosynthesis were largely quantitative rather than qualitative.     

Isolation and bicarbonate transport of chloroplast envelope membranes from species of differing net photosynthetic efficiency

A three-phase discontinuous sucrose gradient yielded two fractions of chloroplast envelope membranes from spinach (Spinacia oleracea L.), sunflower (Helianthus annuus L.), and maize (Zea mays L., mesophyll and undifferentiated chloroplasts). These species were selected to represent plants with fast photorespiration and slow net photosynthesis, fast photorespiration yet fast net photosynthesis, and slow photorespiration and fast net photosynthesis, respectively. Buoyant densities were 1.08 and 1.11 g cm^-3. The light fraction contained primarily single (incomplete) membrane vesicles and the heavy fraction double (complete) ones. Enzymic, chemical, and electron microscopic examination of the complete envelope membranes showed a lack of microbial, microsomal, mitochondrial, and lamellar membrane contamination as well as stromal contamination. Envelope membranes for all species examined were found to contain 2 to 4% of the total chloroplast protein and yields of about 0.2 to 0.4 mg of protein were obtained from 40 g leaves. An Mg²⁺-dependent nonlatent ATPase, a marker enzyme for chloroplast envelope membranes, had the following activities (μmoles of phosphate released/hr^-1 mg protein^-1): spinach, 77; sunflower, 163; old maize, 126; and young maize, 87. Bicarbonate transport was directly correlated with levels of ATPase activity in spinach and sunflower envelope membranes. Transport of HCO₃⁻ with sunflower envelope membranes approached that of young maize.     

Reproductive Allometry in Soybean, Maize and Sunflower

We compared the relationship between grain yield per plant (Y_P)and shoot biomass per plant (S_P) in three annual crops withcontrasting reproductive strategies: sunflower, a determinatespecies with a single inflorescence; maize, a determinate specieswith a limited capacity to adjust the number of ears in responseto resource availability; and indeterminate soybean, a specieswith a large capacity to adjust the number of inflorescences.Our working hypotheses were: H₁—the relationship betweenY_PandS_P is linear; H₂—the intercept of the model is zero,i.e. there is not a threshold plant mass for reproduction. Awide range of Y_Pand S_Pwas generated by manipulation of plantdensity;S_Pvaried between 0.3 and 196 g per plant in soybean,between 6 and 873 g per plant in sunflower and between 23 and697 g per plant in maize. Within these broad ranges of plantsize, both hypotheses were rejected in five out of six experiments,i.e. the relationship between Y_Pand S_Pdeparted from linearityand there was a threshold for S_Pbelow which no grain set occurred.TheS_P threshold for grain set varied widely among species; itwas close to 2 g per plant for soybean, 27 g per plant for sunflowerand 43–71 g per plant for maize. Because of this sizethreshold and non-linearity, harvest index (HI = Y_PS_P^-1) wasstable for mid-size plants, diminished slightly for large plants,and diminished sharply for smaller plants in all three crops.Harvest index stability was highest in soybean, intermediatein sunflower and lowest in maize. Differential stability ofreproductive partitioning partially derived from contrastingpatterns of meristem allocation. Copyright 2000 Annals of BotanyCompany Helianthus annuus L., Zea mays L., Glycine max(L.) Merrill, grain yield, harvest index, plant density, reproductive allocation, meristem allocation, plasticity     

Examination of a Model and Data Describing the Effect of Temperature on the Respiration Rate of Crop Plants

Some of the published evidence used in the synthesis and maintenancemodel of plant respiration is discussed in relation to the effectof temperature. Recalculations from the data of de Vries (1975b) give different results from those claimed by him. The modelis considered in terms of the use of substrate in the dark andits production in the light. It is suggested that starvationestimates of maintenance are not valid. The most reliable methodof observing synthesis respiration in whole plants appears tobe by following a discrete pool of substrate, as is possiblewith labelled carbon. Triticum aestivum L., Zea mays L., Helianthus annuus L., Vicia faba L., carbon dioxide, respiration, temperature, substrate content     

Leaf enlargement and metabolic rates in corn, soybean, and sunflower at various leaf water potentials

Rates of photosynthesis, dark respiration, and leaf enlargement were studied in soil-grown corn (Zea mays), soybean (Glycine max), and sunflower (Helianthus annuus) plants at various leaf water potentials. As leaf water potentials decreased, leaf enlargement was inhibited earlier and more severely than photosynthesis or respiration. Except for low rates of enlargement, inhibition of leaf enlargement was similar in all three species, and was large when leaf water potentials dropped to about −4 bars.     

The uptake of persistent organic pollutants by plants

In a field experiment, the transfer of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) from contaminated soil to maize (Zea mays L.), sunflower (Helianthus annuus), poplar (Populus nigra × P. maximowiczii) and willow (Salix × smithiana) and the distribution of PCB congeners in maize and sunflower was investigated. The former waste incinerator in Hradec Králové (Czech Republic) was chosen for the experiment. Results of plot screening showed heterogenous contamination by PCBs and PAHs. PCB soil contamination was evidently caused by Delor 106 or Aroclor 1260 stocking and PAH contamination by chemicals containing fluoranthene, benzo/b/fluoranthene, phenanthrene and pyrene. Tested plants were planted on a contaminated field site, in soil contaminated with 1530 μg/kg of total PCBs and 0.138 and 3.42 mg/kg of total PAHs. The results show that maize and sunflower roots accumulated the most PCBs from soil. These plants accumulated hexa- and heptachlorobiphenyl congeners more than tri-, tetra-, and pentachlorobiphenyl congeners. Total concentrations of PAHs in tested plants ranged from 0.096 to 1.34 mg/kg. The highest phenanthrene concentration was found in aboveground biomass of sunflower and the highest concentration of pyrene, in maize roots.     

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     

Correlations between proton-efflux patterns and growth patterns during geotropism and phototropism in maize and sunflower

By placing seedlings of sunflower (Helianthus annuus L.) or maize (Zea mays L.) on agar plates containing a pH indicator dye it is possible to observe surface pH patterns along the growing seedling by observing color changes of the indicator dye. Using this method we find that in geotropically stimulated sunflower hypocotyls or maize coleoptiles there is enhanced proton efflux on the lower surface of the organ prior to the initiation of curvature. As curvature develops the pattern of differential acid efflux becomes more intense. A similar phenomenon is observed when these organs are exposed to unilateral illumination, i.e. enhanced acid efflux occurs on the dark side of the organ prior to the initiation of phototropic curvature and the pattern of differential acid efflux intensifies as phototropic curvature develops. These observations indicate that differential acid efflux occurs in response to tropistic stimuli and that the acid efflux pattern may mediate the development of tropistic curvatures.     

Structure, Production and Leaf Area Dynamics: A Comparison of Lodgepole Pine and Sunflower

Populations of lodgepole pine (Pinus contorta var latifoliaEngelm) and sunflower (Heltanthus annuus L) were examined tocompare the influence of stand density on canopy structure andthe association between canopy structure and the productionof stem volume The plastic responses of canopy structure tocompetitive interactions indicated that the structural dynamicsof lodgepole pine and sunflower populations were similar, thoughthe degree of plastic response differed The influence of canopystructure on the production of stem volume, however, was fundamentallydifferent efficiency decreased as the mean crown size of lodgepolepine populations increased, but this decrease did not occurin sunflower populations This difference was attributed to thelarge accumulation of branch biomass required to display foliageeffectively in the canopies of the perennial lodgepole pine,accumulation which does not occur in the annual sunflower Lodgepole pine, Pinus contorta var latifolia Engelm, sunflower, Helianthus annuus L, leaf area, canopy structure, stand production, carbon allocation     

Plant Growth Analysis: Growth and Yield Component Responses to Population Density in Forage Maize

Forage maize (Zea mays L.) was grown in monocultures at populationdensities ranging from 4·9 to 11·1 plants m^–2.Data for plant growth analysis were obtained from six harvestscarried out from 21 to 115 d after planting. Conventional plantgrowth analysis indicated that improvements in forage productivityper unit land area by high population density resulted directlyfrom increased plant presence. Reduction in dry weight per shootat high population density was associated with reduced unitleaf rate. Leaf area ratio was little affected, which may implythat competition for soil nutrients or oxygen was the chiefcause of plant interference. Yield component analysis demonstratedthe increasing importance of population density treatments asa source of variation as growth progressed. Direct relationshipsbetween variation in yield per plant and variation in two yieldcomponents, stem diameter and the inverse of leaf area ratio,were demonstrated. Both conventional plant growth analysis andyield component analysis indicated complex physiological andmorphological adjustments to species population density. Plant growth analysis, yield component analysis, Zea mays L     

Changes in RNA and Protein Metabolism Associated with Alterations in the Germination Efficiency of Sunflower Seeds

Precise knowledge of seed quality after harvest and during storageis of particular importance for seed producers. We analyseddifferent sunflower seed lots (Helianthus annuusL.) characterizedby extremes of germination ability. We used RNA analysis tostudy possible changes in gene expression in seeds unable togerminate. Total RNA content was very small in dry seeds showinga low germination ability. Capacity for total RNA synthesisat the onset of imbibition was also reduced in these seeds.In addition, correlations were found between these parametersand germination ability at 19 °C. We demonstrated a highcorrelation between the amount of total RNA in the dry seed,the capacity of RNA synthesis at the onset of imbibition andthe seed moisture content at the time of the harvest. The abilityof dry seed mRNAs to be translatedin vitrowas also reduced andseven polypeptides, from stored mRNAs, were characteristic ofthe cotyledons from high germinability seeds. Germination canthus be affected at several levels including membrane, enzymaticand nucleic acid deteriorations. Gene expression; germination ability; Helianthus annuusL.; marker; protein; RNA; seed; sunflower