The behaviour of 14C profiles in Helianthus seedlings

Summary The log. ¹⁴C activity/distance profile in the stems of Helianthus seedlings consists of two main parts: region 1, the linear advancing front and region 2, which is also linear but with a less steep slope. As the front passes down the stem, the slope of region 1 remains constant but the amplitude of the front becomes attenuated. The attenuation increases with temperature. The apparent velocity of the profile, which can be derived from the position of the front, is also temperature dependent. Small amounts of ¹⁴C occur in the stem ahead of the profile; these amounts increase with a rise of temperature. Region 2 behaves differently: its slope decreases steadily with time but it is insensitive to temperature. The behaviour of this region is dependent on the movement of tracer into an immobile fraction as well as on the longitudinal movement of tracer in the translocation stream.     

Bidirectional translocation of sugars in sieve tubes of squash plants

Two streams of sugars moving in opposite directions in the petiole of a half-grown leaf were demonstrated by feeding tritiated glucose to a fully grown leaf of a squash plant (Cucurbita melopepo Bailey) and ¹⁴CO₂ to the half-grown one. Autoradiographic evidence indicates that the movement of both streams occurred within the same sieve tubes. The data do not fit the mass flow theory of translocation which requires unidirectional flow of sugar solution in the lumen of the sieve tube.     

The effect of protease digestion (in situ) on the slime substance of mature sieve tubes

Summary The sieve tube slime of Tetragonia and Lycopersicum petiolar phloem was subjected to proteolytic enzymes both before and after embedding and sectioning. Subsequent electron microscopical examination confirmed that the fibrillar material is protein in nature, and provided evidence that the protein is acidic rather than basic.     

Fine structure of the proteinaceous substance in sieve tubes

Summary The dense pore-filling substance in the sieve plates of dicotyledons seems to consist of fibrils, rather than systems of membranes.

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Zusammenfassung Die dichte Substanz, welche bei Dicotyledonen die Poren der Siebplatten ausfüllt, scheint eher aus Fibrillen als aus Membransystemen zu bestehen.

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With 6 Figures in the Fext     

Some observations on the role of ATP in sieve tube translocation

Summary Using the aphid stylet technique ¹⁴C ATP was shown to be readily taken up into the sieve elements of willow. At the same time this compound was found to be metabolised during uptake resulting in labelled ADP and AMP appearing in the stylet exudate. Longitudinal movement of labelled ATP was also found to occur.Measurement of the levels of ATP and ADP in stylet exudate showed that both were present in high concentrations. The ratio ATP/ADP varied between 2.0 and 5.3.The effect of certain inhibitors of oxidative phosphorylation (oligomycin and DNP) and glycolysis (fluoride) on the rate of stylet exudation was studied. All three inhibitors caused a cessation of exudation but this did not occur until several hours after inhibitor application. Oligomycin and DNP had no effect on the concentration of ATP in the sap. Fluoride however, appeared in some cases to reduce the ATP concentration to a low level an hour or more before exudation finally stopped.Incorporation of ³²Pi into organic phosphate esters present in stylet exudate was found to occur within 15 minutes of the application of the tracer to a bark strip. Labelling of organic phosphates also took place, at a slower rate, when ³²P inorganic phosphate was incubated with stylet exudate.     

The effect of low temperature on sucrose,ATP and potassium concentrations and fluxes in the sieve tubes of willow

Summary Experiments have been performed on the effect of localised low (0°C) temperature application on solute concentration and fluxes in the sieve elements of willow. Sieve tube exudate was obtained via the severed stylets of the aphid Tuberolachnus salignus (Gmelin). In stem segments, low temperature caused a fall in both the concentration and flux of sucrose. No recovery was observed during a 24 h cold application period. The concentrations of ATP and potassium were generally also reduced, though the effect on the fluxes of these solutes was not as marked. Both ATP and potassium appear to be translocated along the sieve tubes of stem segments as evidenced by girdling experiments. In leafy cuttings low temperature consistently reduced the concentration of sucrose in the sieve tube exudate. These data are discussed in relation to previous work on low temperature effects on the phloem transport system of willow.     

The influence of calcium deficiency on the translocation of photosynthetically fixed 14C in soybeans

Summary Soybean (Glycine max (L.) Merr.) plants were grown at two levels of Ca (0.05 and 2.5 mM Ca) with and without an inorganic source of N in a growth chamber and in the greenhouse. The fourth leaf from the top of the plant was labeled with ¹⁴C, and the distribution of ¹⁴C was measured 24 hours after labeling. The translocation of ¹⁴C out of the labeled leaf was decreased at the low Ca level in both experiments. This decrease occurred before there were any visual Ca deficiency symptoms and before the low Ca level had any effect on dry weight accumulation. The effect of the low Ca level on translocation was the same for plants exposed to an inorganic N source and those that were nodulated. The reduced rate of translocation from the labeled leaf had no measurable effect on the nodule activity as measured by the acetylene reduction method. The data demonstrate the importance of an adequate supply of Ca to the soybean plant for maximum translocation of carbohydrates from the leaves.This paper (76-3-110) is published with the approval of the Director of the Kentucky Agric. Exp. Stn.This paper (76-3-110) is published with the approval of the Director of the Kentucky Agric. Exp. Stn.     

Effect of manganese on zinc-65 absorption by rice seedlings and its translocation within the plants

Summary Effect of manganese on absorption and translocation of zinc by rice seedlings was studied in a nutrient solution using radioactive zinc (Zn⁶⁵). With increase in manganese application, zinc uptake decreased in roots, but increased in shoots with an application upto 10 M manganese. Reduction in zinc absorption was more at low rates of zinc application. However, translocation of zinc from roots to shoots increased with manganese application upto 20 M but the increase was more pronounced with an application of 2M zinc only.     

Pattern of glucose-14C catabolism in barley seedlings during vernalization

The pattern of glucose catabolism in barley shoots during vernalizationwas examined using glucose-1-¹⁴C and glucose-6-¹⁴C. The pentosephosphate pathway became progressively predominant over theEmbden-Meyerhof-Parnas (EMP) pathway after germination in unvernalizedseedlings, while the EMP pathway maintained a superior positionduring the corresponding developmental stages in seedlings undervernalization. (Received August 20, 1973; )     

14C2H4: Distribution of 14C-labeled tissue metabolites in pea seedlings

The ¹⁴C-metabolite distribution pattern following ¹⁴C₂H₄ metabolismin intact pea seedlings (Pisum sativum L.) was determined undervarious conditions. After a 24 hr exposure to ¹⁴C₂H₄, the majorityof ¹⁴C-metabolites were water-soluble (60–70%) with lesseramounts in the protein (10–15%), lipid (1%), and insoluble(1–2%) fractions. Ion exchange chromatography of the water-solublecomponents into basic, neutral, and acidic fractions revealeda 50 : 40 : 10 distribution, respectively. Chromatography ofthe neutral fraction revealed two regions of radioactivity (Rf=0.38)and 0.63 which did not cochromatograph with twenty-two knownsugars or neutral metabolites. Chromatograms of the basic fractioncontained 3 regions of radioactivity. Similar distribution patternswere noted when ¹⁴C₂H₄ exposure was followed by a 6 hr air chaseor when 5% CO₂, an antagonist of ethylene action, was presentduring the exposure. Marked differences in the ¹⁴C-metabolite distribution patternswere obtained when ¹⁴CO₂ was substituted for ¹⁴C₂H₄. These resultsindicate that the metabolic pathway involved in ethylene metabolismis different from that involved in intermediary carbon metabolism. ¹ Contribution No. 2338 from Central Research and DevelopmentDepartment, Experimental Station, E. I. du Pont de Nemours andCompany, Wilmington, Delaware. (Received June 28, 1976; )     

Effects of acifluorfen on auxin translocation in bean seedlings

The effect of 5-(2-chloro-4-(trifluoromethyl)phenoxy)-2-nitrobenzoic acid (acifluorfen) on the translocation of the¹⁴C-labeled auxins 2,4,5-trichlorophenoxyacetic acid (2,4,5-T-1-¹⁴C) and indole-3-acetic acid (IAA-1-¹⁴C) was determined. The auxins and acifluorfen were injected into the stem at the cotyledonary node of 9-day-old bean (Phaseolus vulgaris L. cv Tenderpod) seedlings. The plants were harvested 4 h after treatment and analyses of¹⁴C were made of various plant parts. Acifluorfen increased 2,4,5-T,-1-¹⁴C translocation out of the treated area and especially into the large primary leaves. This translocation pattern is indicative of apoplastic translocation and suggests that acifluorfen inhibited vein loading of the auxins. Acifluorfen affected auxin translocation in the dark as effectively as in the light even though the herbicidal effects of acifluorfen are known to be expressed only after light treatment.Journal article no. 4403 of the Agric. Exp. Stn., Oklahoma State Univ.     

Methyl jasmonate effects on ethylene synthesis and organ-specific senescence in Helianthus annuus seedlings

Both methyl jasmonate (MJ) and ethylene have been implicated in promoting senescence, but the specific roles of each and the mechanisms by which they act are not well known. We tested the possibility that MJ and ethylene interact to promote senescence. In sunflower seedlings, the ability of MJ to affect ethylene metabolism was investigated in hypocotyls, cotyledons, and leaves. 1-aminocylcopropane-1-carboxylic acid (ACC)-dependent ethylene production was promoted to different extents depending on the organ and the age of the tissue. Newly emerged hypocotyls were sensitive to MJ, but became desensitized as the cotyledons emerged. The cotyledons increased and peaked in MJ sensitivity from emergence to the production of the primary leaves. Leaves were found to be somewhat insensitive to MJ treatment compared to cotyledons at all ages tested. In cotyledons, MJ also promoted ACC and ethylene production. However the changes in ACC, and ACC-dependent ethylene production were not directly correlated with those in ethylene production with respect to MJ concentration or tissue age. Moreover, changes in ACC-dependent ethylene production did not correlate with in vitro ACC oxidase activity. We hypothesized that MJ affects ethylene production by increasing the spatial access of ACC to ACC oxidase perhaps through increased membrane permeability. Ethylene was not involved in the MJ-induced loss of chlorophyll. But the breakdown of cell integrity and cell membranes (estimated by monitoring conductivity of the solution that bathed the cotyledons) was greatly and synergistically promoted by the combination of MJ and ethylene. Promotion of membrane breakdown by MJ and ethylene could be inhibited by treatments with ethylene inhibitors (STS or CoCl₂), and neither MJ nor ACC treatment alone could induce as much membrane breakdown as both together. We suggest that MJ and ethylene interact to accelerate some aspects of senescence in specific organs for nutrient remobilization for the benefit of the whole plant.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - MJ methyl jasmonate - STS silver thiosulphate     

The effect of translocation on movement behaviour—A test of the assumptions of behavioural studies

Animal movement behaviour is intensively investigated with capture-mark-recapture studies. For the analysis of such experiments, the influence of marking technique, handling and translocation of marked animals on movement pattern is of crucial importance since it may mask or overrule the effects of the main research question. Here we present a capture-mark-recapture experiment on the movement behaviour of the blue-winged grasshopper Oedipoda caerulescens. We analyzed the influence of translocation of individuals from familiar to unfamiliar sites. Our study clearly demonstrates a significant influence of translocation to unfamiliar sites on the movement behaviour of O. caerulescens. Translocated individuals moved longer distances, showed smaller daily turning angles, and thus movements were more directed than those of resident individuals. The effect of translocation on daily moved distances was most pronounced on the first day of the experiment. We thus conclude that at least for the first day after translocation, movement behaviour is significantly influenced by translocation itself. Data ignoring this influence will be unsuitable for the prediction of dispersal behaviour, habitat detection capability or habitat preference.     

The fine structure of the sieve tubes of Salix caprea (L.) and its relation to the electroosmotic theory

Summary The sieve plate pores of Salix caprea in preparations fixed in glutaraldehyde are normally found to be occupied by slime fibrils showing periodic banding such as occur in a number of other species. Arguments are put forward to suggest that the occurence of fibrils in this position is natural and not an artefact of preparation. The sieve tubes further possess prominent and persistent nucleoli showing a radiating structure of tubules. The endoplasmic reticulum often occurs in parietal stacks reminiscent of other species.This evidence is discussed in relation to the electroosmotic theory of translocation.This work formed part of that submitted for the degree of Ph. D. of the University of London by U. Mishra.     

Ion selectivity of the anthrax toxin channel and its effect on protein translocation

Anthrax toxin consists of three ∼85-kD proteins: lethal factor (LF), edema factor (EF), and protective antigen (PA). PA₆₃ (the 63-kD, C-terminal portion of PA) forms heptameric channels ((PA₆₃)₇) in planar phospholipid bilayer membranes that enable the translocation of LF and EF across the membrane. These mushroom-shaped channels consist of a globular cap domain and a 14-stranded β-barrel stem domain, with six anionic residues lining the interior of the stem to form rings of negative charges. (PA₆₃)₇ channels are highly cation selective, and, here, we investigate the effects on both cation selectivity and protein translocation of mutating each of these anionic residues to a serine. We find that although some of these mutations reduce cation selectivity, selectivity alone does not directly predict the rate of protein translocation; local changes in electrostatic forces must be considered as well.     

Differential organelle movement on the actin cytoskeleton in lily pollen tubes

We have examined the arrangement and movement of three major compartments, the endoplasmic reticulum (ER), mitochondria, and the vacuole during oscillatory, polarized growth in lily pollen tubes. These movements are dependent on the actin cytoskeleton, because they are strongly perturbed by the anti-microfilament drug, latrunculin-B, and unaffected by the anti-microtubule agent, oryzalin. The ER, which has been labeled with mGFP5-HDEL or cytochalasin D tetramethylrhodamine, displays an oscillatory motion in the pollen tube apex. First it moves apically in the cortical region, presumably along the cortical actin fringe, and then periodically folds inward creating a platform that transects the apical domain in a plate-like structure. Finally, the ER reverses its direction and moves basipetally through the central core of the pollen tube. When subjected to cross-correlation analysis, the formation of the platform precedes maximal growth rates by an average of 3 s (35-40 degrees ). Mitochondria, labeled with Mitotracker Green, are enriched in the subapical region, and their movement closely resembles that of the ER. The vacuole, labeled with carboxy-dichlorofluorescein diacetate, consists of thin tubules arranged longitudinally in a reticulate network, which undergoes active motion. In contrast to the mitochondria and ER, the vacuole is located back from the apex, and never extends into the apical clear zone. We have not been able to decipher an oscillatory pattern in vacuole motion. Because this motion is dependent on actin and not tubulin, we think this is due to a different myosin from that which drives the ER and mitochondria.     

The influence of plant water deficit on photosynthesis and translocation of 14C-labeled assimilates in cacao seedlings

The effect of plant status on net assimilation and translocation of "C-labeled assimilates in cacao (Theobroma cacao L.) was evaluated. As plant water potential (ψ) decreased from −0.5 to −1.0 MPa, neither net assimilation nor the rate of label translocation out of the l4CO,-fed leaf were affected, but as iji fell between −1.0 and −1.5 MPa, net assimilation decreased sharply and label retention increased greatly. Translocation out of source leaves was strongly correlated with net assimilation (r =−0.93). Translocation velocity, assessed by detection of labeled assimilates in sink leaves, was sensitive to plant water deficit, and it declined linearly (r = 0.97) throughout the range of leaf water potentials observed. The results may be explained by reduction in the velocity of assimilate movement within the sieve elements, reduction in supply of labeled assimilates from source leaves, reduction in sink strength or diversion of assimilates to sites of storage or utilization.