Progress in the genetic manipulation of crops aimed at changing starch structure and increasing starch accumulation

The starch content and its composition have important consequences for the yield of the harvested crop and the materials extracted from it. The functional properties of the foods or other processed materials derived from these crops are also affected by the structure and composition of the starch. Recently, genetic engineering has been used to produce plants with an elevated starch content, achieved by transforming the plant with a mutated bacterial gene coding for an ADPglucose pyrophosphorylase that is active in the presence of metabolites which inhibit the plant enzyme. Besides the practical implications of these results, this experiment provided direct evidence for the regulatory role of the ADPglucose pyrophosphorylase in starch synthesis. Other bacterial enzymes, such as glycogen synthase and branching enzyme, could be introduced in order to modify starch structure. However, a more elegant (but longer-term) approach would be to learn enough about the structure-function relationships of the plant enzymes so that the product of their action could be changed. To achieve this objective, much more will have to be learned about the enzymes involved in the biosynthesis of starch than is presently known. Here, the basic properties of starch and the current research approaches to understanding its biosynthesis are described, together with a perspective of how genetic manipulation of starch structure may be achieved.Paper presented at the Bio/Environmentally Degradable Polymer Society—Third National Meeting, June 6–8, 1994, Boston, Massachusetts.     

Woody plant roots fail to penetrate a clay-lined landfill: Managment implications

In many locations, regulatory agencies do not permit tree planting above landfills that are sealed with a capping clay, because roots might penetrate the clay barrier and expose landfill contents to leaching. We find, however, no empirical or theoretical basis for this restriction, and instead hypothesize that plant roots of any kind are incapable of penetrating the dense clays used to seal landfills. As a test, we excavated 30 trees and shrubs, of 12 species, growing over a clay-lined municipal sanitary landfill on Staten Island, New York. The landfill had been closed for seven years, and featured a very shallow (10 to 30-cm) soil layer over a 45-cm layer of compacted grey marl (Woodbury series) clay. The test plants had invaded naturally from nearby forests. All plants examined—including trees as tall as 6 m—had extremely shallow root plates, with deformed tap roots that grew entirely above and parallel to the clay layer. Only occasional stubby feeder roots were found in the top 1 cm of clay, and in clay cracks at depths to 6 cm, indicating that the primary impediment to root growth was physical, although both clay and the overlying soil were highly acidic. These results, if confirmed by experimental research should lead to increased options for the end use of many closed sanitary landfills.     

Disturbance of natural vegetation by camping: Experimental applications of low-level stress

Previously undisturbed sites in four different vegetation types were camped on for one night and for four nights. Changes in vegetation cover and vegetation height were measured after camping and one year later. Results are presented separately for different campsite zones—parts of the site where campers slept, cooked meals, and stored their packs. Just one night of camping was sufficient to cause evident impact in all four vegetation types, although the amount of impact varied significantly between zones and between vegetation types. Vegetation impact on campsites used four nights was generally less than twice as severe as impact on the sites used one night. The effects of camping on vegetation were also predicted for 12 other vegetation types on the basis of vegetational responses to experimental trampling. These results suggest that impact can almost always be minimized by confining camping to a small number of campsites instead of dispersing use across many campsites.     

ENSO and Disaster: Droughts, Floods and El Niño/Southern Oscillation Warm Events

The connection between El Niño/Southern Oscillation (ENSO) events and precipitation and temperature variability worldwide is increasingly well understood. ENSO has been linked to droughts and flooding in some regions. This paper uses the disaster history database of the U.S. Agency for International Development's Office of U.S. Foreign Disaster Assistance to examine the link between ENSO events and droughts or floods of sufficient magnitude to trigger international disasters. Worldwide, disasters triggered by droughts are twice as frequent during year two of ENSO warm events than during other years. No such relationship is apparent in the case of flood disasters. Drought disasters occur during year two of ENSO warm events significantly more frequently than in other years in Southern Africa and Southeast Asia. No regional pattern emerges from a comparable analysis of flood disasters. Those places likely to be affected by ENSO-triggered droughts can take proactive measures to mitigate the impacts.     

THE EFFECTS OF A MOVING RAINSTORM ON DIRECT RUNOFF PROPERTIES1

ABSTRACT: The effects of a moving rainstorm on flood runoff characteristics were investigated. A flood hydrograph simulation model called “FH-Model” and a natural watershed were used. A hypothetical rainstorm of 50 years recurrence interval, 75 mm depth, and 4 hours duration was used to show the effects of velocity and direction of the moving rainstorm on the runoff characteristics. Compared with an equivalent stationary rainstorm (ESRS), the peak flow caused by a rainstorm moving in a downstream direction with a speed equal to channel velocity, V, was 27.5 percent higher and the peak flow caused by the same rainstorm moving in an upstream direction was 21.7 percent smaller. These percentages reduced to 10.5 percent and 8.6 percent for storms moving downstream and upstream, respectively, at three times the channel velocity, 3V. There were negligible differences in the time of peak, T_p between runoff caused by storms moving downstream and runoff produced by ESRS. However, T_p for a storm moving upstream at V velocity was 82 percent higher than that produced by ESRS, but was reduced to 27 percent higher when the storm velocity was 3V.     

Determination of optimum minimum flow from a dam by using energy analysis

The proposed restoration of an abandoned hydroelectric dam on the Quinebaug River, Connecticut, is studied using energy analysis. The analysis considers the effects of alternative minimum flow releases, ranging from 0 to 34 cubic meters per second (cms), on the total energy flow of the affected system. The principal system components affected by differing minimum flows are hydroelectric power generation, aquatic habitat, and gross aquatic ecosystem productivity.The minimum flow alternative resulting in the highest annual energy flow in the affected system is considered optimal. From this purely analytical point of view, the optimum minimum flow is 0 cms, due to the short length and low productivity of the regulated reach, and the lack of floodplain interactions.Simulations of longer and more productive river reaches were conducted. For very short, unproductive reaches, in the absence of a floodplain, the contribution of aquatic community productivity to total system energy flow is negligible compared to hydroelectric generation. Optimum minimum flows are higher for longer and more productive reaches. For such cases the operation of hydroelectric dams could reduce total system energy flow because the energy supplied by hydroelectric generation may be offset by losses in aquatic productivity due to diminished riverine habitat.