Relationships between feeding of Philaenus spumarius (L.) and the amino acid concentration in the xylem sap

Summary. 1. P.spwnarius nymphs selected young, upper leaves of Xanthium strumarium plants, which have a relatively high amino acid concentration in the xylem sap.
2. Nymphs selected or rejected a host leaf as a feeding site after a test ingestion of plant sap.
3. Nymphs fed on detached leaves kept with their petioles in a solution of amino acids, in preference to leaves with petioles in a solution containing no amino acids.
4. Nymphs caged on leaves with relatively high amino acid concentrations in the xylem sap suffered a lower mortality after 7 days than nymphs caged on leaves with low amino acid concentrations in the xylem sap.
5. Mean excretory rate increased with the increase in the amino acid concentration in the xylem sap for third and fourth instar nymphs, and adults, but not in fifth instars.     

Uptake and distribution of potassium in tomato plants

Summary The uptake and distribution of potassium was examined in tomato plants, cv. Amberley Cross and Moneymaker, grown in peat/loam and given a nutrient feed either adequate or deficient in potassium.Detailed studies were also made of the distribution of potassium in various parts of tomato plants, cv. Amberley Cross, grown in sand and supplied with nutrient feeds containing four and seven concentrations of potassium. In these plants the concentration of potassium in stem, petiole and laminar tissue increased from the base to the apex of plants, irrespective of the potassium concentration in the nutrient feed. There was also a gradient of decreasing potassium concentration along leaves, from proximal to distal laminae. The concentration of potassium in all plant parts increased with increasing nutrient supply of potassium, petioles showing a greater response to nutrient potassium than laminar tissue.Marginal chlorosis and/or necrosis were observed when the potassium concentration in fully expanded leaves fell below 1.2 per cent of the dry weight for cv. Amberley Cross or 1.5 per cent for cv. Moneymaker. A 50 per cent incidence of chlorosis and/or necrosis occurred in leaf laminae containing 0.74 per cent potassium.Leaves rarely showed deficiency symptoms when the concentration of potassium in the petioles was higher than that in adjacent laminar tissue. However, chlorosis and/or necrosis occurred when the potassium concentration in petioles fell below that in laminae. In the diagnosis of the potassium status of tomato plants, the most suitable tissue for sampling for potassium analysis is considered to be the petioles of young fully expanded leaves.     

Stomatal Closure in Flooded Tomato Plants Involves Abscisic Acid and a Chemically Unidentified Anti-Transpirant in Xylem Sap

We address the question of how soil flooding closes stomata of tomato (Lycopersicon esculentum Mill. cv Ailsa Craig) plants within a few hours in the absence of leaf water deficits. Three hypotheses to explain this were tested, namely that (a) flooding increases abscisic acid (ABA) export in xylem sap from roots, (b) flooding increases ABA synthesis and export from older to younger leaves, and (c) flooding promotes accumulation of ABA within foliage because of reduced export. Hypothesis a was rejected because delivery of ABA from flooded roots in xylem sap decreased. Hypothesis b was rejected because older leaves neither supplied younger leaves with ABA nor influenced their stomata. Limited support was obtained for hypothesis c. Heat girdling of petioles inhibited phloem export and mimicked flooding by decreasing export of [14C]sucrose, increasing bulk ABA, and closing stomata without leaf water deficits. However, in flooded plants bulk leaf ABA did not increase until after stomata began to close. Later, ABA declined, even though stomata remained closed. Commelina communis L. epidermal strip bioassays showed that xylem sap from roots of flooded tomato plants contained an unknown factor that promoted stomatal closure, but it was not ABA. This may be a root-sourced positive message that closes stomata in flooded tomato plants.     

The role of mineral nutrients in the increased growth response of tomato plants in solarized soil

Soil solarization is a non-chemical disinfestation technique that frequently promotes plant growth in the absence of known major pathogens, a phenomenon termed increased growth response (IGR). The effect of solarization on plant nutrients and their role in the IGR was studied with tomato plants grown in solarized or non-solarized (control) sandy soil, under controlled conditions. Solarization considerably increased the soil concentrations of water extractable N, K, Ca, Mg and Na at most sites, whereas Cl and DTPA extractable Mn, Zn, Fe and Cu were decreased by the treatment. Plant growth and specific leaf area were enhanced in solarized as well as in N-supplemented control soil. In tomato plants grown in solarized soil, concentrations of most nutrients in the xylem sap, including N, were increased compared to the control, whereas Cl and SO4 levels decreased. The most significant increase in leaf nutrient concentration caused by soil solarization was recorded for N. Furthermore, leaf N concentration was highly and positively correlated with shoot growth. The concentration of Cu increased in leaves from the solarization vs. the control treatment, whereas that of SO4 and Cl decreased, the latter presumably below the critical toxicity level. The correlation between shoot growth and leaf concentration was positive for Cu and inverse for Cl and SO4. In conclusion, we found that soil solarization significantly affects nutrient composition in tomato plants, and provided strong evidence that N, and eventually also Cl, play a major role in IGR.     

Transport of sucrose, not hexose, in the phloem

Several lines of evidence indicate that glucose and fructose are essentially absent in mobile phloem sap. However, this paradigm has been called into question, especially but not entirely, with respect to species in the Ranunculaceae and Papaveraceae. In the experiments in question, phloem sap was obtained by detaching leaves and placing the cut ends of the petioles in an EDTA solution. More hexose than sucrose was detected. In the present study, these results were confirmed for four species. However, almost identical results were obtained when the leaf blades were removed and only petiole stubs were immersed. This suggests that the sugars in the EDTA solution represent compounds extracted from the petioles, rather than sugars in transit in the phloem. In further experiments, the leaf blades were exposed to (14)CO(2) and, following a chase period, radiolabelled sugars in the petioles and EDTA exudate were identified. Almost all the radiolabel was in the form of [(14)C]sucrose, with little radiolabelled hexose. The data support the long-held contention that sucrose is a ubiquitous transport sugar, but hexoses are essentially absent in the phloem stream.     

Transport of organic solutes in Phloem and xylem of a nodulated legume

Collections of xylem exudate of root stumps or detached nodules, and of phloem bleeding sap from stems, petioles, and fruits were made from variously aged plants of Lupinus albus L. relying on nodules for their N supply. Sucrose was the major organic solute of phloem, asparagine, glutamine, serine, aspartic acid, valine, lysine, isoleucine, and leucine, the principal N solutes of both xylem and phloem. Xylem sap exhibited higher relative proportions of asparagine, glutamine and aspartic acid than phloem sap, but lower proportions of other amino acids. Phloem sap of petioles was less concentrated in asparagine and glutamine but richer in sucrose than was phloem sap of stem and fruit, suggesting that sucrose was unloaded from phloem and amides added to phloem as translocate passed through stems to sinks of the plant. Evidence was obtained of loading of histidine, lysine, threonine, serine, leucine and valine onto phloem of stems but the amounts involved were small compared with amides. Analyses of petiole phloem sap from different age groups of leaves indicated ontogenetic changes and effects of position on a shoot on relative rates of export of sucrose and N solutes. Diurnal fluctuations were demonstrated in relative rates of loading of sucrose and N solutes onto phloem of leaves. Daily variations in the ability of stem tissue to load N onto phloem streams were of lesser amplitude than, or out of phase with fluctuations in translocation of N from leaves. Data were related to recent information on C and N transport in the species.     

The Occurrence of Translocated Antibiotics in Expressed, Plant Sap

The details of a convenient laboratory press are presented anda procedure by which plant sap is readily obtained is described.The pressing procedure has been shown to release 53–74per cent. of the total plant water as expressed sap. Preliminary observations on the uptake and translocation ofantibiotics by higher plants obtained by examining expressedsap are described. It is shown that the assay of expressed sapprovides a measure of the griseofulvin and chloramphenicol concentrationin leaves of plants grown in solutions of these antibioticsthat does not differ significantly from the value obtained bythe assay of water extracts. Extraction of leaves from plants grown in griseofulvin solutionswith organic solvents demonstrates a much greater antibioticcontent than is indicated by the assay of expressed sap. Toexplain this difference a ‘free’ antibiotic fraction,obtainable in expressed sap or water extracts, and a ‘bound’fraction recovered from the leaf only by organic solvent extractionare postulated.     

THE INFLUENCE OF LIGHT INTENSITY ON THE SUSCEPTIBILITY OF PLANTS TO CERTAIN VIRUSES

Reducing the light intensity under which plants were grown in summer to one-third increased their susceptibility to infection with tobacco necrosis, tomato bushy stunt, tobacco mosaic and tomato aucuba mosaic viruses. With the first two viruses shading increased the average number of local lesions per leaf by more than ten times and by more than five times with the second two.
Reducing the light intensity increased the virus content of sap from leaves inoculated with Rothamsted tobacco necrosis virus by as much as twenty times. As it also reduced the total solid content of sap by about one-half, purification was greatly facilitated; crystalline preparations of the virus were readily made from shaded plants but not from unshaded controls.
Reducing the light intensity also increased the virus content of systemically infected leaves; the greatest effect was with tomato bushy stunt virus with which increases of up to ten times were obtained, but with tobacco mosaic and aucuba mosaic viruses there were also significant increases.
The importance of controlled illumination in raising plants for virus work and the possible mechanisms responsible for the variations in susceptibility are discussed.     

Determination of critical K concentrations in sap from individual leaves or from whole plants using K-interruption experiments

Summary A new method is described for estimating critical K concentrations from K interruption experiments using only 2 treatments. Frequent measurements are made of the growth and K concentration of plants subjected to either continued or interrupted K supply and the data used to define the relation between relative yield and K concentration for the K-deficient plants. Critical concentrations are estimated from the results using a mathematical model of plant growth to interpolate over the critical concentration region of the curve. The method has the advantage that the critical concentrations are determined at the exact time that growth is affected. The method was tested using data from previously published experiments with lettuce in which the concentrations of K were measured in sap from both the total shoot and from individual leaf petioles. The model accurately predicted the form of the relationship between relative yield and K concentration for the total shoot and for young expanding leaves, but consistently deviated from the data for recently matured ones. Average estimates of critical concentration ranged fromca. 18 to 34 mmoll⁻¹ in the young leaves and from 48 to 67 mmoll⁻¹ in the mature ones when Na salts were present or absent respectively. The values for total shoot sap were similar to those for mature leaves. The critical concentrations for young expanding leaves were virtually identical to the minimum believed to be needed for the maintenance of important biochemical processes in individual cells, and suggests that a single critical K concentration for plant sap might apply to a wide range of crops provided an actively growing part of the plant is sampled.     

High external sucrose concentration inhibits the expansion of detached tomato fruits grown in a novel semi-open device

The effect of sap sucrose concentration on fruit expansion is poorly understood. We investigated the effects of sucrose concentration on growth of tomato fruits, detached from the plant after the cell multiplication phase. A semi-open device was built to grow detached fruits, where the fruit pedicel was immersed in a nutrient solution which was automatically replaced each day. About 22 d after anthesis, tomato fruits were harvested, disinfected in alcohol, and placed in the device with a sterile nutrient solution containing 5% sucrose. After about 1 wk, the sucrose concentration was either increased to 15% or maintained at 5%. The fruit expansion rate decreased when the sucrose concentration was increased, and after about 1 wk, these fruits weighed less than those grown at 5% sucrose. Although all the fruits in the device grew much less than those maintained on the plant, a high sap sucrose concentration applied to the excised fruits after the cell multiplication phase inhibited the expansion of tomato fruits. The device and method developed here will be useful for future studies of fruit growth.     

Laurel forests in Tenerife, Canary Islands

The efficiency of the conductive system in about 40-year-old Laurus azorica trees growing in a laurel forest was evaluated by comparing main stems and leaves (petioles) on the basis of theoretical sap flow values (1) calculated from vessel anatomy (taking vessels as ideal capillaries), (2) derived from measured dye velocity and (3) data taken from direct sap flow measurements. It was found that actual sap flow rate per wood area increases in stems from the pith towards the cambium. The outermost part of the stem is the most important part of the tree for conducting water. Maximum actually measured transpiration (sap flow rate) for the stand was practically identical to the theoretical rate calculated based on petiole anatomy, but it was about 45 times lower than that calculated based on stem anatomy. This illustrates the safety features of stem wood, which due to its high vessel density, is capable of transporting all the water required even when only a small area of its vessels is working. In the petioles, xylem is more efficiently used, but almost all vessels must work in order to supply water to leaves and any disturbance may cause leaf loss.     

Immunolocalization of mannitol dehydrogenase in celery plants and cells.

Immunolocalization of mannitol dehydrogenase (MTD) in celery (Apium graveolens L.) suspension cells and plants showed that MTD is a cytoplasmic enzyme. MTD was found in the meristems of celery root apices, in young expanding leaves, in the vascular cambium, and in the phloem, including sieve-element/companion cell complexes, parenchyma, and in the exuding phloem sap of cut petioles. Suspension cells that were grown in medium with mannitol as the sole carbon source showed a high anti-MTD cross-reaction in the cytoplasm, whereas cells that were grown in sucrose-containing medium showed little or no cross-reaction. Gel-blot analysis of proteins from vascular and nonvascular tissues of mature celery petioles showed a strong anti-MTD sera cross-reactive band, corresponding to the 40-kD molecular mass of MTD in vascular extracts, but no cross-reactive bands in nonvascular extracts. The distribution pattern of MTD within celery plants and in cell cultures that were grown on different carbon sources is consistent with the hypothesis that the Mtd gene may be regulated by sugar repression. Additionally, a developmental component may regulate the distribution of MTD within celery plants.     

Analysis of the ethylene response in the epinastic mutant of tomato

Ethylene can alter plant morphology due to its effect on cell expansion. The most widely documented example of ethylene-mediated cell expansion is promotion of the "triple response" of seedlings grown in the dark in ethylene. Roots and hypocotyls become shorter and thickened compared with controls due to a reorientation of cell expansion, and curvature of the apical hook is more pronounced. The epinastic (epi) mutant of tomato (Lycopersicon esculentum) has a dark-grown seedling phenotype similar to the triple response even in the absence of ethylene. In addition, in adult plants both the leaves and the petioles display epinastic curvature and there is constitutive expression of an ethylene-inducible chitinase gene. However, petal senescence and abscission and fruit ripening are all normal in epi. A double mutant (epi/epi;Nr/Nr) homozygous for both the recessive epi and dominant ethylene-insensitive Never-ripe loci has the same dark-grown seedling and vegetative phenotypes as epi but possesses the senescence and ripening characteristics of Never-ripe. These data suggest that a subset of ethylene responses controlling vegetative growth and development may be constitutively activated in epi. In addition, the epi locus has been placed on the tomato RFLP map on the long arm of chromosome 4 and does not demonstrate linkage to reported tomato CTR1 homologs.     

Metal Complexation in Xylem Fluid : I. CHEMICAL COMPOSITION OF TOMATO AND SOYBEAN STEM EXUDATE

Xylem fluid was analyzed for numerous solutes to characterize chemically the sap as a medium for forming and transporting metal complexes. The stem exudate was collected hourly for 8 hours from topped 31-day-old soybean (Glycine max L. Merr.) and 46-day-old tomato (Lycopersicon esculentum Mill.) plants grown in normal (0.5 micromolar) and Za-phytotoxic nutrient solutions. Soybean plants were grown in the normal and high-Zn solutions for 24 days; tomato plants were grown for 32 days. The exudate was analyzed for seven organic acids, 22 amino acids, eight inorganic solutes, apparent ionic strength, and pH. Significant changes in many solutes occurred over the 8-hour sampling period. These fluctuations depended on plant species, individual solute, and Zn treatment, and demonstrated that extrapolation of xylem-fluid analyses to whole-plant xylem sap is valid only for sap samples collected shortly after topping a plant. Exudate pH decreased over the 8-hour period for both species; exudate ionic strength increased for tomato and decreased for soybean. At the normal-Zn treatment (0 to 1 hour), the highest acid micromolar concentrations in soybean exudate were: asparagine, 2,583; citric, 1,706; malic, 890; and malonic, 264. Under the same conditions, the highest acid micromolar concentrations in tomato exudate were: maleic, 1,206; malic, 628; glutamine, 522; citric, 301; and asparagine, 242. Cysteine and methionine were above detection limits only in soybean exudate. Zinc phytotoxicity caused significant changes in many solutes. The analyses reported here provide a comprehensive data base for further studies on metal-complex equilibria in xylem fluid.     

Determination of 1-aminocyclopropane-1-carboxylic acid (ACC) in leaf tissue and xylem sap using capillary column gas chromatography and a nitrogen/phosphorus detector

The Lizada and Yang method, commonly used for analyzing 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of the plant hormone ethylene, is subject to interference and lacks internal standards. The use of combined gas chromatography-mass spectrometry (GC-MS) overcomes these shortcomings but the method is expensive and unavailable to many laboratories. We describe an alternative physico-chemical method using a capillary column gas chromatograph fitted with a standard nitrogen/phosphorus detector. After forming the N-benzoyl n-propyl derivative, measurements of ACC concentrations in extracts of leaves and in xylem sap of tomato plants using the nitrogen/phosphorus detector were within 10% of those obtained by GC-MS. Concentrations in plants grown in well-drained soil were approximately 0.16 nmol g^–1 fresh weight (leaves) and 0.04–0.01 mmol m^–3 (sap). Flooding the soil for 48–72 h increased these values approximately 9-fold.     

Assimilation and Transport of Nitrogen in Nonnodulated (NO(3)-grown) Lupinus albus L

The response of nonnodulated white lupin (Lupinus albus L. cv. Ultra) plants to a range of NO₃ levels in the rooting medium was studied by in vitro assays of extracts of plant parts for NO₃ reductase (EC 1.6.6.1) activity, measurements of NO₃-N in plant organs, and solute analyses of root bleeding (xylem) sap and phloem sap from stems and petioles. Plants were grown for 65 days with 5 millimolar NO₃ followed by 10 days with 1, 5, 15, or 30 millimolar NO₃. NO₃ reductase was substrate-induced in all tissues. Roots contained 76, 68, 62 and 31% of the total NO₃ reductase activity of plants fed with 1, 5, 15, and 30 millimolar NO₃, respectively. Stem, petioles, and leaflets contained virtually all of the NO₃ reductase activity of a shoot, the activity in extracts of fruits amounting to less than 0.3% of the total enzyme recovered from the plant. Xylem sap from NO₃-grown nonnodulated plants contained the same organic solutes as from nodulated plants grown in the absence of combined N. Asparagine accounted for 50 to 70% and glutamine 10 to 20% of the xylem-borne N. The level of NO₃ in xylem sap amounted to 4, 13, 12, and 17% of the total xylem N at 1, 5, 15, and 30 millimolar NO₃, respectively. Xylem to phloem transfer of N appeared to be quantitatively important in supplying fruits and vegetative apices with reduced N, especially at low levels of applied NO₃. NO₃ failed to transfer in any quantity from xylem to phloem, representing less than 0.3% of the phloem-borne N at all levels of applied NO₃. Shoot organs were ineffective in storing NO₃. Even when NO₃ was supplied in great excess (30 millimolar level) it accounted for only 8% of the total N of stem and petioles, and only 2 and 1% of the N of leaflets and fruits, respectively.     

The Effects of Temperature on Vegetative and Early Reproductive Growth of a Cold-Tolerant and a Cold-Sensitive Line of Phaseolus vulgaris L. 2. Nodular Uricase, Allantoinase, Xylem transport of N and Assimilation in Shoot Tissues

The activities of nodular uricase and allantoinase, the compositionof bleeding sap N, estimated rates of xylary N translocationand ureide assimilation in shoot tissues were compared in acold-tolerant (194) and sensitive (Seafarer, SF) line of nodulatedPhaseolus vulgaris grown under three different temperature regimes.Uricase activity increased with increasing growth temperatureand was generally greater in nodules of 194 than in SF at anyparticularly temperature. Extractable allantoinase activity,on the other hand, was highest in nodules from plants grownat the coolest temperature (15/10 C day/night) and there waslittle or no difference in activity between the lines. There was little difference in sap composition between linesor amongst temperature treatments. Ureides contributed between80–91 percent of the total sap N in both lines grown at25/15 or 20/15 C with a slightly lower per cent (65–84)when grown at 15/10 C. Estimated rates of N translocation werehigher in 194 than SF at the coolest growth temperature. Increasesin rates of N translocation between successive harvests of eitherline were often correlated with increases in total N accumulationand also an accumulation of ureides in stems plus petioles butnot leaves. Generally leaves assimilated all of the ureidesinto other compounds at all growth temperatures. Nodules andshoots of either line did not accumulate ureides at 15/10 C.194 Accumulated greater amounts of ureides in stems and petiolesthan SF when grown at the two warmer temperatures. The resultsare discussed in relation to the ability of 194 to fix greateramounts of N than SF at suboptimal growth temperatures. Phaseolus vulgaris, common bean, uricase, allantoinase, sap composition, ureide assimilation, low temperature stress     

Cucumber mosaic virus movement protein affects sugar metabolism and transport in tobacco and melon plants

In addition to its influence on plasmodesmal function, tobacco mosaic virus movement protein (TMV‐MP) causes an alteration in carbon metabolism in source leaves and in resource partitioning among the various plant organs. The present study was aimed at characterizing the influence of cucumber mosaic virus (CMV)‐MP on carbohydrate metabolism and transport in both tobacco and melon plants. Transgenic tobacco plants expressing the CMV‐MP had reduced levels of soluble sugars and starch in their source leaves and a significantly reduced root‐to‐shoot ratio in comparison with control plants. A novel virus‐vector system was employed to express the CMV‐coat protein (CP), the CMV‐MP or the TMV‐MP in melon plants. This set of experiments indicated that the viral MPs cause a significant elevation in the proportion of sucrose in the phloem sap collected from petioles of source leaves, whereas this sugar was at very low levels or even absent from the sap of control melon plants. The mode by which the CMV‐MP exerts its effect on phloem‐sap sugar composition is discussed in terms of possible alterations in the mechanism of phloem loading.     

施用磷对王桉 (Eucalyptus regnans F. Muell.)幼苗生长及其氨基酸组

王桉 (Eucalyptus regnans F. Muell.) 是澳大利亚桉树中最重要的商业用材和人工造林树种之一.研究王桉的施肥与其体内氨基酸的积累和转化及与食叶虫害之间的相关性具有重要的经济和生态意义.在温室内利用2种不同来源的土壤对王桉幼苗进行了不同磷施用量(100 kg hm~(-2)和 200 kg hm~(-2))处理.结果显示,不同土壤和不同磷施用量对苗木生长影响显著,但均未显著影响苗木各部分的氮和磷含量水平.苗木木质部渗出液中的氨基酸含量以谷氨酰胺为主,并与苗木生长和磷施用量呈反相关.不同土壤和磷施用量对苗木组织中游离氨基酸组分和含量的影响不显著,但游离氨基酸的组分和相对水平随叶龄变化明显,尤其是精氨酸在嫩叶氨基酸总量中只占2%～3%,但在老叶中占到20%多;精氨酸在老叶中的积累极有可能是某些蛋白质降解而精氨酸即时合成所致,因为精氨酸一般不在韧皮部转运.谷氨酰胺在树液中含量最高并与苗木生长呈反相关或许可以作为预测桉树发生食叶昆虫危害的一个有用指标.     

Differential peroxidase activities in three different crops upon insect feeding

Peroxidases are the ubiquitous enzyme and reported to be present in all living genera. They catalyses reduction of peroxide and generate reactive oxygen species. In the present study we demonstrated that insect infestation induces peroxidase activity in sap and total soluble protein (TSP) of plant leaves. Three important crop plants viz. tomato, cowpea and cotton were used for this study. After infestation of chewing insect, Peroxidase activity in the sap and TSP of all the studied plants were enhanced in the range of 1.6 to 3.14 fold. Similar observations were also obtained with feeding of sap sucking insects, in which increment in peroxidase activity of sap and TSP was in the range of 1.8 to 2.53 fold. Enhanced peroxidase activity was reconfirmed by in-gel peroxidase assay. Enzyme kinetic study showed turn over efficiency of peroxidase from cotton (~101.3 min^-1) was almost similar to tomato (~100.8 min^-1) but higher than cowpea (~98.21min^-1). MS/MS analysis of observed band showed significant similarity with the reported peroxidases in database.