THE RELATIONSHIP BETWEEN NICKEL-TOXICITY SYMPTOMS AND THE ABSORPTION OF IRON AND NICKEL

During a 70-day experimental period from germination to maturity, the iron content of oat plants that showed symptoms of nickel toxicity changed little, but the nickel content increased rapidly for about 30 days and then decreased slowly. Necrosis varied little with time, while chlorosis increased in severity for 40 days, then decreased until unfolding young leaves were no longer chlorotic. This change in chlorotic symptoms was correlated with the nickel-iron ratio in the plant.
Autoradiographs of leaves from plants supplied with radioactive iron showed that necrotic areas in the leaf matched areas in the autoradiograph having a very low content. Chlorotic areas were found to correspond with areas whose iron content was lower than that of healthy tissue. More iron was found in the veins than in the interveinal tissue, and its distribution was the same whether supplied as ferric citrate or in a chelated form.
The concentration of iron in mature leaves from oat plants growing in a nickel toxic soil was lowest in the necrotic areas of the leaf, suggesting a migration of nutrients out of this dying tissue.     

Effects of Copper Toxicity on Leaves of Oregano (Origanum vulgare subsp. hirtum)

The effects of increasing concentrations of soil copper on anumber of leaf structural parameters in oregano plants werestudied to determine the effect of copper toxicity. Copper-stressedleaves were small and chlorotic and underwent a thickening oftheir lamina, due principally to an increase in the number andvolume of mesophyll cells. The number of stomata and glandularand non-glandular hairs increased significantly. Chloroplastsof mesophyll cells declined dramatically in number and volume.Grana and stroma thylakoids of chloroplasts did not undergoany noticeable alterations, but starch grains disappeared, plastoglobulibecame larger and the double membrane limiting the chloroplastbecame dilated. Leaf chlorosis was determined by total chlorophyllanalysis and measurement of the leaf Cu, Fe and Mg content.The effects of copper toxicity on oregano leaves comprised significantstructural alterations which reflect reduced metabolic activity.Copyright 2001 Annals of Botany Company Origanum vulgare subsp, hirtum, oregano, copper toxicity, leaf, structure and ultrastructure, morphometry, inorganic elements, tissue relative volumes     

Development of plants from leaf discs of variegatedColeus and its relation to patterns of leaf chlorosis

Summary Leaf discs approximately 8 mm in diameter taken from green and from chlorotic areas of variegated leaves ofColeus were grown in light under sterile conditions in a mineral salt, sucrose, vitamin medium supplemented with auxin and cytokinin. Green shoots, which later formed roots, grew from both green and chlorotic discs in media containing suitable amounts of auxin and cytokinin. None developed in media supplemented with auxin alone or with cytokinin alone. Discs with young plants were transferred to soil. Plants that grew varied widely from those with no chlorosis to those with more chlorosis than the original variety from which the discs were taken. Plants grown from discs taken from green areas of leaves with chlorosis varied in patterns of chlorosis as much as those that grew from discs from chlorotic areas of leaves. This research was supported, in part, by The Conservation and Research Foundation.     

Nucleic Acid Metabolism in the Developing Primary Leaf and Senescing Coleoptile of Germinating Oats

Nucleic acid metabolism in the coleoptile and primary leaf tissues of the germinating oat (Avena sativa L.) seedling was studied. The concentrations of the different species of nucleic acid present at various stages of development were determined and the amounts of each compared. All species of nucleic acid in the coleaptile increased as the tissue elongated; but, with the onset of senescence all species decreased, especially rRNA. Exposing dark grown coleoptiles to light did not modify their capacity to synthesize nucleic acids. In the rapidly developing leaf, all species of nucleic. acid increased throughout early germination. A general enhancement in the synthesis of all species of nucleic acids resulted when dark-grown-leaves were exposed to light. Furthermore, the tRNA/DNA ratio remained constant in both tissues during development, whereas the rRNA/DNA ratio changed.     

Studies in the Nutrition of Apple Rootstocks: II. Effects of Concentration of Iron in the Nutrient Solution on Growth and Chlorophyll Content

Rooted one-year shoots were grown for one season by sprayingtheir roots with nutrient solution. Iron supplied as Fe-EDTAat four concentrations resulted in plants which were respectively(a) severely chlorotic, (b) mildly chlorotic, (c) dark greenand healthy (controls), and (d) dark green but with slight reductionin growth. Severely deficient plants showed 40–70 per cent reductionsin growth as measured by fresh weight, shoot length, diameterincrease, leaf area, net assimilation and relative growth-rates.Dry weights were reduced 70–80 per cent and of the totaldry-weight increment a greater proportion remained in the leaves,which had a lower dry weight and higher water content per unitarea. However, because the initial old stem formed a greaterproportion of the total dry weight, the leaf area ratio remainedabout 11 per cent lower than in the controls. Severely deficientplants had, per unit of chlorophyll, a higher dry-weight increaseand net assimilation rate than the controls. Mild deficiency caused 10–20 per cent reductions in growthand net assimilation rate; the leaf area ratio was normal. Possible mechanisms of the effects of low iron supply are discussed,while the small growth reduction at the highest Fe-EDTA concentrationis attributed to chelate toxicity     

Growth Regulator Interactions in the Growth of the Shoot System of Avena sativa Seedling: II. THE GROWTH OF THE FIRST LEAF AND THE COLEOPTILE1

1. Studies have been made of the growth in culture medium of thecomponent parts of compositesegments excised from 3 to 7-day-oldAvena sativa seedlings and comprising portions of coleoptileand first leaf bases and various lengths of first internodetissue.
2. The effects of various concentrations of gibberellicacid (GA)and indole-3- acetic acid (IAA) alone and in combinationhavebeen studied on the growth of these organs.
3. Both GA andIAA stimulate the growth of coleoptile base tissuebut in combinationtheir joint effects are less than additive.No synergism occurs.
4. The growth of the first-leaf base is greatly stimulated byGAbut is inhibited by IAA. In combination, the stimulatoryeffectof GA (up to 1 0 p.p.m.) may be virtually eliminatedby evenlow concentrations of IAA (0.01 p.p.m.).
5. The inclusionof first internode tissue in the segments considerablyincreasesthe growth of first leaf base tissue but has no consistenteffecton the growth of coleoptile base tissue. The presenceof firstinternode tissue also greatly increases the degreeof growthstimulation invoked by GA but does not influence thedegreeof IAA inhibition. It is postulated that the first internodetissue is the source of an unknown growth factor necessary forGA action in the first leaf and potentiating the action of endogenousgibberellin.
6. Kinetin, adenine sulphate, glutarnine, glutarnicacid, asparagine,glycine, arginine, histidine, lysine, aneurin,and pyridoxinewill not simulate the effects of this unknowngrowth factorin the growth of leaf tissue. Like IAA, kinetinvirtually eliminatesthe GA stimulation of leaf growth.
7. Astudy of extracts of internode tissue in various solvents,analysedby paper partition chromatography and assayed by thegrowthof the first leaf base, has indicated the presence ofgrowthinhibitors and gibberellin-like substances but has failedtoisolate the postulated endogenous GA-synergist.
8. The implicationsof these results for growth correlations andthe hormone controlof shoot growth in Avena sativa seedlingsis discussed.

     

Exposure of oat seedlings to blue light results in amplified phosphorylation of the putative photoreceptor for phototropism and in higher sensitivity of the plants to phototropic stimulation

Dark recovery of blue light-induced in vitro phosphorylation in oat (Avena sativa L.) seedlings after in vivo preirradiation with blue light revealed different recovery kinetics for the coleoptile base and tip. Although, in both cases, maximum in vitro phosphorylation was observed 90 min after in vivo blue light treatment, the phosphorylation levels for the entire base were about 3-fold higher than those found in nonpreirradiated plants. The tip response only slightly exceeded that of the dark controls. The fluence applied during preirradiation determined the extent of the increase in phosphorylation. Consequently, unilateral irradiation and subsequent dark incubation resulted in a more pronounced increase in phosphorylation in the irradiated than in the shaded side of the coleoptile base. Furthermore, blue light-irradiation conditions, known to induce neither first- nor second-positive curvature in nonpreirradiated plants, stimulated both asymmetric distribution of protein phosphorylation and second-positive phototropic curvature in the coleoptile base when administered to blue light-pretreated plants. Based on these data, we conclude that photosensitivity of the coleoptile base increases upon exposure to blue light in a time-and fluence-dependent manner, providing an excellent explanation of the invalidity of the Bunsen-Roscoe reciprocity law for second-positive phototropism.     

VIRUSES CAUSING ROSETTE AND OTHER DISEASES IN GROUNDNUTS

From plants with a form of groundnut rosette disease, characterized by discrete areas of green and chlorotic tissue on the leaflets and here designated 'mosaic rosette', a virus was separated that produced only a mild mottle or sometimes a mottle with rare chlorotic flecks. It was separated by leaf grafts, by mechanical inoculation and by Aphis craccivora .
Plants inoculated simultaneously with the mottle virus and normal rosette virus usually developed the mosaic-rosette symptoms. When the mottle virus was introduced 14–35 days before the rosette virus, the plants failed to develop the severe chlorosis of rosette; the mottle virus thus protected the plant from rosette, and this was true whether the rosette virus was inoculated by aphids or by grafting.
Plants showing two other forms of mild mottle were collected in the field; viruses from them were readily transmitted by grafting or by mechanical inoculation, but not by A. craccivara . In plant-protection tests with one of these, it failed to protect plants from developing chlorotic symptoms when later inoculated with the rosette virus, although a form of interaction was evident and the doubly-infected plant was less severely chlorotic and less stunted than one infected with the rosette virus alone.     

The Relationship between the Growth of the Primary Leaf and of the Coleoptile in Seedlings of Avena and Triticum

Partial inhibition of extension growth of the primary leaf occurswhen whole Triticum seedlings are immersed in aerated solutionsof IAA but is replaced by growth promotion when sucrose is addedto the external solution. In seedlings in which the coleoptilehas been excised, IAA increases the growth of the leaf bothwith and without additional sucrose. Inhibition of the leaf by moderate concentrations of IAA nolonger occurs when the seedling is detached from the endosperm.Sucrose added to the external solution raised the percentageelongation of the coleoptile almost to the level of that attainedin intact seedlings without additional carbohydrate. It alsoenabled the leaf to show a positive growth response with IAA. The results indicate that in intact seedlings treated with IAAthe growth of the primary leaf is markedly diminished owingto diversion of carbohydrate to the coleoptile if the growthof the latter is promoted as a result of the treatment. Whenthe competition of the coleoptile for carbohydrate is diminishedor eliminated, acceleration of the growth of the primary leafby IAA becomes apparent. In addition to the endogenous rhythm, with a period close to24 hours, induced in the growth-rate of the coleoptile whenseedlings of Avena are transferred from red light to darkness,a similar rhythm, with a slightly longer period, is inducedin the growth-rate of the primary leaf. This rhythm persistsin elongating leaves so long as they remain within the coleoptile.It can be recorded for at least 100 hours in deseeded seedlings. When intact seedlings of Avena are immersed for one hour inrelatively high concentrations of IAA and then transferred todistilled water for 18 hours, the elongation of the coleoptileis greater and the inhibition of the leaf is less than whenthey are transferred to humid air. Sections of the leaf of Triticum showed a slight increase inelongation in concentrations of IAA up to 5 mg./l., but no evidencewas obtained that sections of leaf and coleoptile exert any.influenceon each other's elongation when floated together on solutionsof IAA.     

Influence of Iron Chlorosis on Pigment and Protein Metabolism in Leaves of Nicotiana tabacum L

Experiments were conducted on Nicotiana tabacum, L. to study the relation in the grana among chlorophylls, carotenoids, and proteins. The effect of iron chlorosis on protein and pigment synthesis was studied at different stages of chlorosis using glycine-U-C¹⁴. Pigments were separated by thin layer chromatography.

Chlorophyll a, chlorophyll b, carotenoid, and protein contents of chloroplasts from chlorotic tissue were less than those of normal tissues. A 25% decrease in protein labeling and a 45% decrease in chlorophyll labeling was noted in deficient tissue compared to normal tissue even before chlorosis was perceptible. Both normal and iron deficient leaf discs which received iron in the incubation medium incorporated higher amounts of radioactive glycine into chlorophyll a and chlorophyll b at all stages of development than their respective counterparts not supplied with iron in the incubation medium. The presence of iron in the incubation medium reduced the amount of glycine incorporated into carotenes and xanthophylls, except where the tissue was severely chlorotic. This may be attributed to active competition for glycine between the iron-dependent- (chlorophyll) and iron-independent-(carotenoid) biosynthetic pathways. Incorporation of glycine into chloroplast pigments was lowest at severe chlorosis, probably due to a reduction in the overall enzyme activity.

     

Heavy Metal Toxicity and Iron Chlorosis

1. The toxicity of copper, nickel, cobalt, zinc, chromium, andmanganese to mustard was studied in water culture, utilizingeither the ionic form or the EDTA chelate of the metal in thepresence of either ferric chloride or ferric EDTA. 2. In presence of ferric chloride the activity of the metalsin producing chlorosis was as given above, i.e. in the orderof stability of their chelates. In the presence of ferric versenate,toxicity of the ionic metal was much reduced. The metal chelatesgave very little indication of toxicity with either form ofiron. 3. It was found that the ratio of total phosphorus to totaliron was higher in chlorotic plants than in green plants, irrespectiveof which metal was causing the toxicity. 4. Copper could be demonstrated in the phloem cells of the rootusing bis-cyclohexanone-oxalydihydrazone as histochemical reagent.It is postulated that transport of iron probably takes placein the phloem as an active process. 5. It would appear that as a major part of the iron in plantcells is attached to nucleo- or phospho-proteins, the heavymetals must be similarly attached to phospho-proteins.     

The Morphology of Germination in Setaria lutescens (Gramineae): The Effects of Covering Structures and Chemical Inhibitors on Dormant and Non-dormant Florets

The sequence of organ emergence in embryos of the yellow foxtailgrass (Setaria lutescens) is similar to that reported for othergrasses: coleorhiza, radicle, coleoptile and first leaf. Thecoleorhiza emerges by forcing open a hinged flap on the lemma.Coleorhiza trichomes form soon after emergence. The radicleprotrudes through the abaxial surface of the coleorhiza. Thecoleoptile elongates in a downward direction initially as itpasses between the lemma and palea, but immediately turns upward.The first leaf emerges by protruding through a slit-like creaseon the adaxial surface of the coleoptile. Embryos excised fromdormant florets are shown to germinate as well as those fromnon-dormant florets. Experiments are described which show theinhibitory effects of the embryo covering structures; the lemma,palea and caryopsis coat. Other experiments are discussed concerningthe effects on germination of the inhibitors abscisic acid andcycloheximide. An intermediate concentration of cycloheximide(10^–4 M) does not decrease germination percentage, butrather inhibits radicle growth but no coleoptile elongation.The significance of these observations is discussed.     

THE RELATIONSHIP BETWEEN NICKEL TOXICITY AND IRON SUPPLY

The influence of varying levels of iron and substrate pH on the uptake of nickel and the intensity of toxicity symptoms in oat plants have been investigated using sand-and water-culture techniques.
Nickel-toxicity symptoms (both necrosis and chlorosis) are less severe when the concentration of iron in the nutrient solution is high. The reduction in degree of necrosis is related to a reduced content of nickel in the leaf blades, whilst that of chlorosis is related to the Ni/Fe ratio in the leaf blades—an internal antagonism being indicated in the latter case.
A reciprocal relationship exists between the nickel and iron contents of the leaf blades; the nickel content is materially reduced by high concentrations of iron in the nutrient solution, and the iron content by nickel, the former being the more pronounced effect.
Uptake of nickel increases with increasing pH for a constant iron level in the substrate, although the degree of necrotic symptoms is similar over pH range 4–7. Iron uptake is reduced by both nickel and increasing pH and results in chlorosis at pH values of 5·5 and above.
For a constant level of iron supply the phosphate content of the stem extracts is higher the greater the degree of nickel toxicity; the phosphorus status of the plant may be a factor in producing nickel toxicity but if so, it has to be considered in relation to other factors.     

TRACE-ELEMENT TOXICITIES IN OAT PLANTS

Excessive amounts of nickel, cobalt, chromium, copper, zinc, manganese, molybdenum and aluminium in nutrient solutions supplied to oat plants in sand culture produce ( a ) chlorosis and ( b ) other symptoms specific to the element involved. The specific symptoms are distinct for each metal, although those of cobalt and nickel might be confused.
The toxic effects of nickel, cobalt, copper, zinc, manganese and molybdenum are associated with high concentrations of the element in the leaf tissue, but this is not always so with chromium and aluminium.
The toxic effects of nickel, chromium, copper and molybdenum are associated with a reduced nitrogen content of the plant. Nickel, cobalt, chromium, zinc and manganese increase the concentration of phosphorus in the tissue whilst aluminium decreases it, probably to a deficiency level.
Aluminium reduces the intensity of toxic symptoms produced by nickel—probably by reducing the uptake of nickel and phosphorus. Copper effectively reduces the leaf necrosis produced by nickel, but not the nickel content of the leaf tissue; it is suggested that one factor in nickel toxicity may be inhibition of one or more functions of copper. The other elements slightly increase chlorosis and some increase necrosis.
The order of activitjl of the elements in producing chlorosis is found to be Ni>Cu>Co>Cr>Zn>Mo>Mn. This order, which is related to that giving yield reduction and is similar to the order of stability of metal complexes, is discussed in relation to induced iron deficiency.     

Ethylene Release from Leaves of Xanthium strumarium L. and Zea mays L.

The release of ethylene into sealed Erlenmeyer flasks by intactleaves and leaf discs of Xanthium strumarium L. a C₃ plant andZea mays L. a C₄ plant were compared both in white light andin darkness. The effects of the presence or absence of addedCO₂ (in the form of sodium bicarbonate) the photosynthetic inhibitor3-[3,4-dichlorophenyl]-l, l-dimethyl urea (DCMU) and 1-aminocyclopropane-1-carboxylicacid (ACC), the precursor of ethylene in higher plants, werealso investigated. The rate of ethylene release from leaf tissue of Xanthium inthe absence of added CO₂ was markedly reduced in the light (i.e.at the CO₂ compensation point). Treatments that would enhancethe CO₂ availability to the tissue (i.e. added bicarbonate,darkness, treatment with DCMU) allowed higher levels of ethylenerelease. Incubation of the tissue with ACC considerably enhancedthe release of ethylene compared to that from the correspondingcontrol tissue without ACC. However, the pattern of ethylenerelease induced by the various treatments was similar with orwithout added ACC. When tissue, in the absence of added CO₂, was transferred fromlight to darkness, and back to light for 90 min periods, theethylene release rates Increased during the interposed darkperiod but resumed the lower rate during the final light period.The addition of CO₂ in the light resulted in a similar rateof ethylene release to that found in the dark. The overall pattern of ethylene release from Zea leaf tissuesubjected to light and dark in the presence or absence of addedCO₂ was similar to that of Xanthium. However, two or three timesmore ethylene was released from maize leaves in the light whenCO² was added compared to that generated in the dark. This isin marked contrast to Xanthium, where, under the light conditionsused, the ethylene release rate in the dark equalled or exceededthat occurring in the light, even in the presence of high levelsof CO₂. A very low rate of ethylene release was observed atthe CO₂ compensation point of maize. A speculative model is presented to explain how photosyntheticactivity might act as a key factor in regulating ethylene evolutionfrom leaf tissue in these experiments. It invokes the conceptof an inhibition by CO₂ of ethylene retention or breakdown thuspermitting more ethylene to be released from the leaves.     

Photobiology of phytochrome-mediated growth responses in sections of stem tissue from etiolated oats and corn

The far-red reversibility of the phytochrome-controlled stimulation of elongation of coleoptile sections by low fluence red light has been characterized in subapical coleoptile sections from dark-grown Avena sativa L., cv Lodi seedlings. The fluence dependence of the far-red reversal was the same whether or not the very low fluence response is also expressed. The capacity of far-red light to reverse the red light-induced response began to decline if the far-red light was given more than 90 minutes after the red irradiation. Escape was complete if the far red irradiation was given more than 240 minutes after the red irradiation. Sections consisting of both mesocotyl and coleoptile tissue from dark-grown Avena seedlings were found to have physiological regulation of the very low fluence response by indole 3-acetic acid and low external pH similar to that seen for sections consisting entirely of coleoptile tissue. The fluence-dependence of the red light-induced inhibition of mesocotyl elongation was studied in mesocotyl sections from dark grown Zea mays L. hybrid T-929 seedlings. Ten micromolar indole 3-acetic acid stimulates the control elongation of the sections, while at the same time increasing the sensitivity of the tissue for the light-induced inhibition of growth by a factor of 100.     

Abscission in Coleus: Light and Phytohormone Control

Light control of leaf abscission in Coleus (Coleus blumei Benthcv. Ball 2719 Red) appears to be regulated by the quantity ofendogenous auxin transported from the leaf blade to the abscissionzone. Gas chromatographic—mass spectrophotometric analysisindicated that diffusate collected from leaf tissue treatedwith red light contained significantly higher levels of auxinthan dark and far-red light-treated leaf tissue. In addition,diffusate from red light-treated tissue inhibited abscissionof leafless petioles while diffusate from far-red light-treatedtissue promoted abcission when compared with diffusate fromdark-treated tissue. The effect of red light on abscission couldbe mimicked by IAA, but not by other phytohormones. An auxintransport inhibitor, 2, 3, 5-triiodobenzoic acid (TIBA), appliedeither as a lanolin ring around the petiole or vacuum infiltratedinto tissue, could completely eliminate any red light effecton abscission. The data are consistent with a phytochrome-mediatedlight regulation of endogenous auxin level in the leaf whichthen controls abscission. Key words: Abscission, Coleus, IAA, plant hormones, red (far-red) light, TIBA     

Effect of red light on coleoptile growth

The effects of red light in reducing the growth of the oat (Avena sativa L.) coleoptile and the synthesis of auxin in the coleoptile tip are detectable 2 hours after treatment and become more pronounced with time. When the coleoptile tip is supplied with additional tryptophan the synthesis of auxin is doubled both in darkness and when exposed to red light. Treatment of the tip with gibberellic acid or pyridoxal phosphate overcomes the reduction of auxin synthesis caused by red light. The uptake of exogenous indoleacetic acid, at pH 6.5, by coleoptile tissue is doubled by exposure to red light. The effect of red light on coleoptile growth appears to be mediated by phytochrome in the cell membrane which delocalizes the tryptophan utilized for auxin synthesis.     

Glycerolipid Synthesis in Avena Leaves during Greening of Etiolated Seedlings IV. Effect of Light on Fatty Acid Desaturation

Etiolated Avena sativa L. leaves were fed with [l-¹⁴C]acetatefor 20 h in the dark and labeled fatty acids in glycerolipidswere chased during 24 h in the light (greening condition) orin the dark, to determine the light effect on the fatty aciddesaturation. Oleate decrease in phosphatidylcholine was thesame in the light and in the dark, showing that oleate desaturationis independent of light (or greening). Linoleate desaturationin galactolipids, especially in monogalactosyl diacylglycerol,was enhanced by light and palmitate desaturation to hexadecenoatein phosphatidylglycerol was strictly light-dependent. (Received May 11, 1983; Accepted August 16, 1983)     

In vitro nitrate reductase activity and in vivo phytochrome measurements of maize seedlings as affected by various light treatments

Concomitant in vivo assays of phytochrome and in vitro assaysof nitrate reductase (NR) were made with mesocotyls of Zea maysL. seedlings. NR assays were also made using the potentiallychlorophyllous portions (leaf and coleoptile) of the same shoots.A negative relationship was found between phytochrome levelsand NR activities in response to various light treatments. Noqualitative differences occurred between the NR responses ofmesocotyl and potentially chlorophyllous or chlorophyllous tissues.Exposure of dark-grown seedlings to continuous white light causedrapid losses of assayable phytochrome accompanied by rapid increasesin NR activities. Subsequent return of the seedlings to darknessproduced increases in assayable phytochrome and decreases inNR activity. A brief, red-light treatment given at the end ofthe white-light treatments resulted in more NR activity andless assayable phytochrome in the subsequent dark period thana treatment with far-red light. These data suggest that modulationof NR activity is not directly influenced by photosyntheticphotoreceptors and that phytochrome is involved in the photocontrolof NR activity. Results also indicate that light quality atthe end of the day influences both night NR activity as wellas time required to reach maximal NR activity during the nextphotoperiod. ¹ Mississippi Agricultural and Forestry Experiment Station cooperating. (Received December 2, 1977; )