Plant tissues/residues

To extract phenolic acids in plant tissues/residues ground plant tissues/residues were extracted with water, EDTA, citrate plus or minus imidazole, KCl, or dibasic sodium phosphate and the water-autoclave procedure (Blum et al. 1992 Blum 1997). For procedures used for " C-labeled phenolic acids see Section 2.2.10... 

Materials, Methods, and Commentary 3.2.1 Soil and Plant Tissue/Residue Analyses... 

Plant tissues/residues of wheat Triticum aestivum L. Coker 916 or 983 or Southern States 555 ), rye Secale cereale L. Abruzzi ), crimson clover Trifolium incamatum L. Tibbee ), and/or subterranean clover (T. subterranean L. Mount Barker ) were collected from litter bags half buried (i.e., the lower half of the bag was located within the soil) in the field plots (Blum et al. 1991) or from the soil surface (Blum 1997 Lehman and Blum 1997 Staman et al. 2001), freeze-dried, and stored in the dark at room temperature. The freeze-dried plant tissues/residues were ground just before analysis in a Wiley mill (20,40 or 60 mesh screen) and then extracted and analyzed by several different procedures ... 

Determine under controlled conditions how phenolic acid-containing plant tissues/residues mixed into soil modify phenolic acid-utilizing bulk-soil and rhizosphere microbial populations. 

Phenolic acids in soils occur either in a free state in the soil solution, reversibly sorbed to soil particles, fixed (irreversibly sorbed) very tightly to soil particles (e.g., recalcitrant organic matter, and clays), and/or on and in living and dead plant tissues/residues ( free , reversibly sorbed, and fixed). Of general interest to plant-plant allelopathic interactions are the free and reversibly sorbed states frequently referred to as the available fraction. Of particular interest is the active fraction of available phenolic acids, the fraction of available phenolic acids that actually interact with seeds, roots and microbes. Unfortunately we presently do not have a means of quantifying the active fraction, thus the focus on the available fraction. 

Water-autoclave extractions were also much more efficient than neutral EDTA extractions in recovering sorbed/fixed phenolic acids from plant tissues/residues (Blum et al. 1992). For example HPLC analysis of EDTA extracts for wheat stubble collected after a wheat harvest contained no detectable phenolic acid peaks. Water-autoclave extracts of this wheat stubble had 11 distinct peaks. Concentrations for ferulic acid, vanillic acid, p-coumaric acid, and p-hydroxybenzoic acid were 33, 22, 1034, and 47 p,g/g dry weight, respectively (Fig. 3.8). On the other hand water and... 

Mean concentrations of available individual benzoic and cinnamic acid derivatives determined in this Cecil soil were small, less than 4 xg/g soil. The sums of 7 individual phenolic acids (0-2.5 cm soil cores) for wheat stubble tilled under/soybean and fallow/soybean soil samples were 58 and 38%, respectively, of wheat stub-ble/soybean soil samples (100% =12.30 0.58 tig/g). The sum of 7 individual phenolic acids for the 0-2.5 cm core samples was approximately 34% higher than for the 0-10 cm core samples. Plant tissues/residues contained greater individual phenolic acid content than soils. For example wheat stubble contained 258 times and wheat straw from half buried litter bags 65 times the p-coumaric acid of wheat no-till Cecil A soils (4 tig/g soil). 

Determine Under Controlled Conditions How Phenolic Acids-Containing Plant Tissues/Residues Mixed into Soil Modify Phenolic Acid-Utilizing Bulk-Soil and Rhizosphere Microbial Populations (Staman et al. (2001) Plenum Publishing Corporation, Excerpts Used with Permission of Springer Science and Business Media)... 

Containing Plant Tissues/Residues Mixed into Soil Modify Phenolic Acid-Utilizing Bulk-Soil and Rhizosphere Microbial Populations (Section 3.4.7)... 

The sample preparation was very simple the sample was centrifuged to remove plant cell residues and 10 pi of the clear juice was placed on the column. This type of separation is common with fruits, vegetables and juices and samples can be obtained by preliminary homogenizing the total tissues and then centrifuging. If it is suspected that the residue still contains significant quantities of the substances of interest, then it can be washed with water or if necessary with solvents and the washings combined with the separated supernatant liquor. The results obtained are shown in figure 15. 

Using established extraction and cleanup methods, followed by GC/FPD and GC/thermionic detection, Carey et al. (1979) obtained detection limits in the ppb range and recoveries of 80-110% in soil and 70-100% in plant tissue. Good sensitivity and recovery were maintained in a simplified extraction procedure of sediments followed by GC/FPD analysis (Belisle and Swineford 1988). Bound methyl parathion residues that were not extracted with the usual methods were extracted using supercritical methanol by Capriel et al. (1986). They were able to remove 38% of the methyl parathion residues bound to soil, but 34% remained unextractable, and 28% could not be accounted for. 

OPPTS 860.1500, p. 16, indicates that 3-5 sampling points should be included in the decline trials. For applications close to the normal harvest time, the RAC may be harvested at selected intervals between the time of final application and a normal harvest or slightly delayed harvest. If the application is made long before the normal harvest, then representative plant tissues (including immature RAC) may need to be harvested in order to stretch the harvest period. A single composite sample is all that is required from each selected time point, but two or more samples may be harvested to reduce uncertainty about the actual amount of residue present at each sample time interval. These decline samples should be collected and treated the same as normal RAC samples. The samples should be frozen as soon as possible after collection. The instructions for decline sample collection and handling described in the protocol should be followed closely. 

One application using MAE is a method to determine imidazolinone herbicides and their respective metabolites in plant tissue." Current residue methodologies for determining imazethapyr (imidazolinone herbicide) and its metabolites in crops involve laborious, time-consuming cleanup procedures after an aqueous/organic extraction. 

Chemicals with allelopathic potential are present in virtually all plant tissues, including leaves, stems, roots, rhizomes, flowers, fruits, and seeds. Whether these compounds are released from the plant to the environment in quantities sufficient to elicit a response, remains the critical question in field studies of allelopathy. Allelochemics may be released from plant tissues in a variety of ways, including volatilization, root exudation, leaching, and decomposition of the plant residues. 

It would seem, therefore, that particularly with oil- and wax-soluble insecticides the older concepts of surface residues on plant tissues should be revised in terms of extrasurface—i.e., above the cuticle—and subsurface—i.e., within or below the cuticle— residues. The latter would in turn be subdivided into cuticular residues and various intracarp residues. 

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