Supercritical fluid extraction and solid-phase extraction of AC 263, 222 and imazethapyr from three Texas soils.

Supercritical fluid extraction (SFE) using CO(2) and solid-phase extraction (SPE) are two technologies recently discussed in the literature as alternatives to Soxhlet and liquid/liquid extraction (LLE). This research compared SFE and SPE extraction efficiency of two imidazolinone herbicides, AC263,222 and imazethapyr, from three soils. Recovery of the herbicides using SFE-CO(2) with a 4.6:1 acetonitrile:acetic acid cosolvent was approximately 80% for Poth and Tremona soils and 60% when extracted from Ships soil with high clay content and high pH. SPE recovery of both herbicides averaged 78% and was not statistically different between soils. Combining SPE disks with a SPE cartridge cleanup procedure provided a faster filtration with cleaner filtrate compared with using SPE C-18 cartridges by themselves. Cleanup was needed after both SFE and SPE disk extraction due to interfering peaks in the chromatography. http://link.springer-ny. com/link/service/journals/00244/bibs/37n4p440.html

Interorgan photosynthate partitioning in alfalfa.

The net partitioning of current photosynthate among vegetative organs of nodulated alfalfa (Medicago sativa L.) was investigated by determining radiolabel distribution from upper and lower source leaves, at different times of day, and during successively longer chase periods. Photosynthate was exported sooner and more completely by a fully expanded lower than by a fully expanded upper source leaf. The radiolabel pulse from the lower source leaf peaked in the main stem within 1.5 hours, in the crown and nodules after 3 hours, in the unexpanded leaves and apex of the main stem after 6 hours, and in the shoots growing from leaf axils on the main stem after 24 hours. The results suggest that the crown, apex, axillary shoots, and nodules both imported and mobilized photosynthate originating at a lower source leaf, while roots and shoots growing from the crown showed net accumulation. The pulse from the upper source leaf was initially rapidly exported by the main stem and imported by the root between 1.5 and 3 hours, but there was no net change of label content of these organs during the ensuing 21 hours. Rapidly growing organs had the highest concentrations, and the largest organs had the highest content of radiolabel. These results provide new information about the accumulation and circulation of photosynthate within the alfalfa plant.

Nitrogen fixation and vegetative regrowth of alfalfa and birdsfoot trefoil after successive harvests or floral debudding.

Nitrogenase-dependent acetylene reduction, leaf, herbage, and root growth, and total nonstructural carbohydrate accumulation of alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculatus L.) were compared to learn how nitrogen fixation capacity and vegetative growth respond to partial (75-85%) or total shoot and leaf removal, and floral debudding. Treatments were imposed on greenhouse-grown plants during two successive harvest cycles.Both species displayed an initial decline in total nitrogenase activity within 2 days of harvest and a subsequent recovery of activity after 10 to 21 days. Rate of recovery varied with the amount of leaf area removed. Periodic flower removal did not significantly alter total nitrogenase activity of either species compared with the unharvested controls. In the first harvest cycle, partial leaf area removal did not affect nitrogenase activity of alfalfa, but activity of trefoil was reduced 56%. In the second harvest cycle, partial leaf area removal reduced total nitrogenase activity of alfalfa 46% and that of trefoil 69%. Complete leaf and shoot removal reduced total nitrogenase activity of alfalfa 78% after the first harvest and 86% after the second harvest.Recovery of nitrogenase activity after harvest paralleled leaf area expansion in both species. After the initial decline following the first partial harvest, total nitrogenase activity and leaf area of alfalfa increased 170 and 500%, respectively. After the initial decline following the second partial harvest, nitrogenase activity and leaf area of alfalfa increased 280 and 800%, respectively. Partly harvested trefoil and completely harvested alfalfa showed similar response patterns. Release of bud dormancy and leaf area expansion after flowering of nonharvested alfalfa apparently caused an increase in nitrogenase activity, but patterns of acetylene reduction and leaf area were not otherwise closely correlated in controls of either species. Decline and accumulation of total nonstructural carbohydrates in both species varied with defoliation treatment. Patterns of nonstructural carbohydrates in root tissue were not closely related to the changes in total nitrogenase activity caused by shoot removal.