The distribution of foliar-applied boron (I1'Bjboric acid) in radish (Raphanus sativus L.) was studied using for analysis of the stable isotopes a technique allowing a high sensitivity: spark-source mass spectrometry.Boron was recovered in the nontreated aerial parts and in the roots; however, the greatest fraction was in the treated leaf. It was possible with a laser-probe mass spectrograph to show that boron was not superficialy located in the treated area but was present in tissues at all levels of depth considered.Many investigations on the uptake and the translocation of nutrients applied to leaves have been carried out with the help of radioactive isotopes (2); however, for elements such as boron, the lack of a convenient radioactive isotope makes similar studies very difficult. Here, two novel techniques are used to determine the distribution of foliar-applied boron; (a) in intact plants by mea-surement of the isotopic ratio "B/'0B using a highly sensitive technique, spark-source MS; and (b) in the tissues ofboron-treated leaves, with a microanalytical method that we have recently developed using the laser-probe mass spectrograph (4). The example of boron is considered because this micronutrient is applied frequently by foliar spraying, particularly when the soil is potentially capable of fixing large amounts of this element (7). The redistribution of boron after foliar application has already been studied by Thellier (6, 10) with the help of an enriched stable isotope and a nuclear reaction (n,a). MATERIALS AND METHODS EXPERIMENTAL PROCEDUREThe experiments were performed on radish (Raphanus sativus L. cv. 18 days). The plants were grown in a greenhouse on a sandsphagnum peat moss mixture (1:2, v/v) supplied with a complete commercial fertilizer and micronutrients. When they were 31 days old, 20 mm H3B03 with Tween 20 (0.1% v/v) was applied to the middle of the lamina of one of the pair of first leaves at a temperature of 25 C and a RH of 70%o.The distribution of boron in the entire plants was determined with plants receiving 2 droplets each of 20 Al boric acid enriched with°B (90.5 ± 0.2 atom %). The localization of boron in the treated part was studied with leaves receiving 3 contiguous droplets each of 2 Al of nonenriched boric acid. In the latter case, a small volume of liquid was applied in order to have a limited and well-defined treated area. With both methods of boron application, the treated leaf was sectioned 24 h after the foliar application and was washed rapidly twice for a total of 60 s in 1 liter distilled H20, and then the different parts, including the treated leaf, hypocotyl, and epicotyl, were freeze-dried.The samples for microanalysis were cut immediately after the washing from the treated leaves to include the area initially in contact with the droplets. They were rapidly immersed in isopentane cooled with liquid N2, then freeze-dried in an apparatus VirTis (model 10-OlOTD) and preserved in a desiccator until analysis. SPARK-SOURCEThe preparation of plant samples and analyses ...
A rod of single crystalline silicon has been subjected to high-power nanosecond laser pulses inducing ultrasonic and shock waves traveling into the bulk of the material. Stroboscopic time-resolved high-energy x-ray diffraction measurements were carried out in situ to probe for strain states in the bulk of the sample. First, a supersonic shock front is observed which moves faster than the longitudinal acoustic phonons. Following the shock front, a much slower bunch of waves travels along the crystal. The x-ray diffraction records obtained in different configurations reflect a strong dependence of the wave propagation on the sample geometry. These results offer an experimental approach for the investigation of coherent phonons, structural phase transformations, plastic deformations induced during shock peening, and for the development of x-ray free-electron-laser optics.
SUMMARYThe elementary composition of the fungal vesicles of Trifolium pratense L. endomycorrhizas was determined using the laser-probe mass spectrography. Anatomical and cytological studies were ilso made so as to locate and describe the Endogonaceae in the infested roots of the host plant. Results obtained with fixed and unfixed samples are compared. The fixatives and embedding procedures are not convenient for elements such as potassium. It appears that the vesicles of 'he Endogonaceae, in addition to their high lipid contents could act as reservoirs for many elements, the principal elements detected being K, Ca, Mg and Na.
The propagation of an ultrashort pulse in a dispersive and dissipative medium may conveniently be described by using a Green's function analysis. The advantage would be that all details of the initial pulse, however short, could be probed by an "infinitely" sharp &pulse and subsequently deciphered in a modified form, after the influence of the medium, at a later time and at a new observation point.The Green's function for a dispersive and dissipative, plasma or dielectric (molecular) medium, is constructed for an infinitely extended threedimensional case by using symbolic algebra for time-differential operators. The solution consists of two parts: a displaced &function part and a Bessel-function part, describing a wake field which for dominating dispersion is of oscillatory nature. F o r a certain ratio between the dispersive and dissipative parameters (plasma frequency and damping) a critical limit is found where the wake oscillations disappear completely.In the particular limits of vanishing dispersion or vanishing dissipation one recovers from the generalized solution the well-known results for a pure conductor (metal) and a pure dispersive medium (cold collisionless plasma) described by the Klein-Gordon equation.The response of the medium to an initially localized ulrashort electromagnetic pulse, of an arbitrary shape, can be expressed by an integral in time and space, of the product of the Green's function and the initial pulse.
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