Loss of pendimethalin in runoff and leaching from turfgrass land under simulated rainfall.

A field study was undertaken to investigate runoff and leaching loss of the herbicide pendimethalin in turfgrass land of loamy sand soil. A series of plots constructed in a golf course fairway were surface-applied with pendimethalin SC formulation at the rate of 2. 25 or 4.50 kg a.i./ha and subjected to simulated rainfall at 2.0 cm/day for 10 consecutive days. Runoff losses of pendimethalin were the highest at the first rainfall and then gradually decreased with time. The first runoff event contained pendimethalin in its highest concentration, and in subsequent runoff samples the concentration decreased exponentially. The ranges of pendimethalin concentration were 80.9-18.2 and 177.4-48.6 microgram/L in the standard and double doses, respectively. Total losses by 20 cm of rainfall for 10 days reached 0.81 and 1.22% of the initial deposits at 2.25 and 4.50 kg a. i./ha, respectively. Pendimethalin concentration in the leachate collected at 30-cm soil depth was quite lower than that in the runoff, and the concentration rapidly decreased from 4.3-4.7 to 0. 2-0.4 microgram/L during the 10 days of rainfall treatment. Soil residue analysis at 45 and 90 days after pendimethalin treatment showed that more than 90% of the residue remained at the top 10 cm of soil depth. Low runoff and leaching confirmed that lateral and downward movement of the herbicide should be limited in turf soil. The half-life of pendimethalin under field conditions was 23-30 days and was not affected by application dose and rainfall treatment, but longer persistence was observed under laboratory conditions. Considering low runoff and leaching, as well as relatively short persistence in soil, it is concluded that little environmental carryover of pendimethalin would be expected in turfgrass land.

Starch and the control of kernel number in maize at low water potentials.

After reproduction is initiated in plants, subsequent reproductive development is sometimes interrupted, which decreases the final number of seeds and fruits. We subjected maize (Zea mays L.) to low water potentials (psi(w)) that frequently cause this kind of failure. We observed metabolite pools and enzyme activities in the developing ovaries while we manipulated the sugar stream by feeding sucrose (Suc) to the stems. Low psi(w) imposed for 5 d around pollination allowed embryos to form, but abortion occurred and kernel number decreased markedly. The ovary contained starch that nearly disappeared during this abortion. Analyses showed that all of the intermediates in starch synthesis were depleted. However, when labeled Suc was fed to the stems, label arrived at the ovaries. Solute accumulated and caused osmotic adjustment. Suc accumulated, but other intermediates did not, showing that a partial block in starch synthesis occurred at the first step in Suc utilization. This step was mediated by invertase, which had low activity. Because of the block, Suc feeding only partially prevented starch disappearance and abortion. These results indicate that young embryos abort when the sugar stream is interrupted sufficiently to deplete starch during early ovary development, and this abortion results in a loss of mature seeds and fruits. At low psi(w), maintaining the sugar stream partially prevented the abortion, but invertase regulated the synthesis of ovary starch and partially prevented full recovery.

Purification and Characterization of Wheat beta(2-->1) Fructan:Fructan Fructosyl Transferase Activity.

Fructans are the major storage carbohydrate in vegetative tissues of wheat (Triticum aestivum L.). Fructan:fructan fructosyl transferase (FFT) catalyzes fructosyl transfer between fructan molecules to elongate the fructan chain. The objective of this research was to isolate this activity in wheat. Wheat (cv Caldwell) plants grown at 25 degrees C for 3 weeks were transferred to 10 degrees C to induce fructan synthesis. From the leaf blades kept at 10 degrees C for 4 days, fructosyl transferase activity was purified using salt precipitation and a series of chromatographic procedures including size exclusion, anion-exchange, and affinity chromatography. The transferase activity was free from invertase and other fructan-metabolizing activities. Fructosyl transferase had a broad pH spectrum with a peak activity at 6.5. The temperature optimum was 30 degrees C. The activity was specific for fructosyl transfer from beta(2-->1)-linked 1-kestose or fructan to sucrose and beta(2-->1) fructosyl transfer to other fructans (1-FFT). Fructosyl transfer from oligofructans to sucrose was most efficient when 1-kestose was used as donor molecule and declined as the degree of polymerization of the donor increased from 3 to 5. 1-FFT catalyzed the in vitro synthesis of inulin tetra- and penta-saccharides from 1-kestose; however, formation of the tetrasaccharide was greatly reduced at high sucrose concentration. 6-Kestose could not act as donor molecule, but could accept a fructosyl moiety from 1-kestose to produce bifurcose and a tetrasaccharide having a beta(2-->1) fructose attached to the terminal fructose of 6-kestose. The role of this FFT activity in the synthesis of fructan in wheat is discussed.

Fructan metabolism in wheat in alternating warm and cold temperatures.

The objective of this research was to develop a system in which the direction of fructan metabolism could be controlled. Three-week-old wheat seedlings (Triticum aestivum L. cv Caldwell) grown at 25 degrees C were transferred to cold temperature (10 degrees C) to induce fructan synthesis and then were transferred to continuous darkness at 25 degrees C after defoliation and fructan degradation monitored. The total fructan content increased significantly 1 day after transferring from 25 degrees C to 10 degrees C in both leaf blades and the remainder of the shoot tissue, 90% of which was leaf sheath tissue. Leaf sheaths contained higher concentrations of fructan and greater portions of high molecular weight fructan than did leaf blades. Fructan content in leaf sheaths declined rapidly and was gone completely within 48 hours following transfer to 25 degrees C in darkness. In leaf blades the invertase activity fluctuated during cold treatment. The activity of sucrose:sucrose fructosyl transferase increased markedly during cold treatment, while fructan hydrolase activity decreased slightly. In leaf sheaths, however, the activity of invertase decreased rapidly upon transfer to cold temperature and remained low. Trends in sucrose:sucrose fructosyl transferase and hydrolase activity in sheaths were the same as those of leaf blades. Sheath invertase and hydrolase activity increased when plants were transferred back to darkness at 25 degrees C, while sucrose:sucrose fructosyl transferase activity decreased. These results indicate that changing leaf sheath temperature can be utilized to control the direction of fructan metabolism and thus provide a system in which the synthesis or degradation of fructan can be examined.

Release of superoxide-dependent relaxing factor(s) from endothelial cells.

In the present work, an experimental system was designed to study superoxide anion radical, implicated as the cause of vascular dilatation. To circumvent its direct effect, we employed a two-bath system. When the endothelial cells (EC) were exposed to electrical field stimulation (EFS) or to a hypoxanthine-xanthine oxidase system in bath A plus its physiological buffer solution suffused on a helical strip of cat basilar artery in bath B, the contraction to 5-hydroxytryptamine (5-HT) was depressed to approximately 40-50% of the control value. The reduction was not elicited on EFS in a state of calcium deficiency or in the absence of EC. The depression could be prevented by pretreatment with superoxide dismutase (SOD), but not with an effective dose of catalase, dimethyl sulfoxide (DMSO), mannitol, or indomethacin. The percent depression of contraction was paralleled by an increase in SOD-inhibitable cytochrome c reduction, which was not associated with cyclic guanosine 3',5'-monophosphate formation. These results suggest that superoxide-dependent relaxing factor is released from EC differently than the endothelium-derived relaxing factor mediated by acetylcholine.