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PubMed2006

Predicting essential components of signal transduction networks: a dynamic model of guard cell abscisic acid signaling.

Plants both lose water and take in carbon dioxide through microscopic stomatal pores, each of which is regulated by a surrounding pair of guard cells. During drought, the plant hormone abscisic acid (ABA) inhibits stomatal opening and promotes stomatal closure, thereby promoting water conservation. Dozens of cellular components have been identified to function in ABA regulation of guard cell volume and thus of stomatal aperture, but a dynamic description is still not available for this complex process. Here we synthesize experimental results into a consistent guard cell signal transduction network for ABA-induced stomatal closure, and develop a dynamic model of this process. Our model captures the regulation of more than 40 identified network components, and accords well with previous experimental results at both the pathway and whole-cell physiological level. By simulating gene disruptions and pharmacological interventions we find that the network is robust against a significant fraction of possible perturbations. Our analysis reveals the novel predictions that the disruption of membrane depolarizability, anion efflux, actin cytoskeleton reorganization, cytosolic pH increase, the phosphatidic acid pathway, or K(+) efflux through slowly activating K(+) channels at the plasma membrane lead to the strongest reduction in ABA responsiveness. Initial experimental analysis assessing ABA-induced stomatal closure in the presence of cytosolic pH clamp imposed by the weak acid butyrate is consistent with model prediction. Simulations of stomatal response as derived from our model provide an efficient tool for the identification of candidate manipulations that have the best chance of conferring increased drought stress tolerance and for the prioritization of future wet bench analyses. Our method can be readily applied to other biological signaling networks to identify key regulatory components in systems where quantitative information is limited.

Abscisic Acid↗
PubMed1994

[Cholera epidemiology in Mozambique: 1973-1992].

The results of an epidemiological analysis of cholera in Mozambique from 1973 to 1992 are described. The project sought to assess the influence of socio-economic and ecological factors the spread of cholera in a country at war. Information about the incidence of cholera and the fatality rate were related to the rainfall and the annual average growth rate of the population in the main cities. Water supply, sanitation and food hygiene were also studied. The high annual average growth rate of the population was found to have a direct linear correlation to the incidence of cholera. The drought of 1991-1992 also played an important role in the increased number of cases of the disease. Cholera has presented an endemic-epidemic pattern determined by: a) the uncontrolled growth of urban population, b) the deterioration of sanitation in urban centers, c) the unhygienic commercialization of food and d) the drought.

Cholera↗
PubMedDate not supplied

[Hunger and mental illness].

Based on a recently-published article on the triad of drought, hunger, and mental illness, in which the main idea is that destitution may be leading to behavioral disorders in the drought-plagued population of the Brazilian Northeast, we reflect on what this so-called 'madness' may represent for this group of people. We attempt to analyze the issue from various disciplinary perspectives, going beyond merely causal explanations and taking into account that the reported disorders entail meanings following the articulation of cognitive, affective, and experiential elements founded on the social and cultural relations of individuals. From this point of view, the respective discourse assumes other interpretations, showing that illness is a singular process of construction.

Brazil↗
PubMed2006

Role of multidecadal climate variability in a range extension of pinyon pine.

Evidence from woodrat middens and tree rings at Dutch John Mountain (DJM) in northeastern Utah reveal spatiotemporal patterns of pinyon pine (Pinus edulis Engelm.) colonization and expansion in the past millennium. The DJM population, a northern outpost of pinyon, was established by long-distance dispersal (approximately 40 km). Growth of this isolate was markedly episodic and tracked multidecadal variability in precipitation. Initial colonization occurred by AD 1246, but expansion was forestalled by catastrophic drought (1250-1288), which we speculate produced extensive mortality of Utah Juniper (Juniperus osteosperma (Torr.) Little), the dominant tree at DJM for the previous approximately 8700 years. Pinyon then quickly replaced juniper across DJM during a few wet decades (1330-1339 and 1368-1377). Such alternating decadal-scale droughts and pluvial events play a key role in structuring plant communities at the landscape to regional level. These decadal-length precipitation anomalies tend to be regionally coherent and can synchronize physical and biological processes across large areas. Vegetation forecast models must incorporate these temporal and geographic aspects of climate variability to accurately predict the effects of future climate change.

Climate↗
PubMed2006

Climate effects on fire regimes and tree recruitment in Black Hills ponderosa pine forests.

Climate influences forest structure through effects on both species demography (recruitment and mortality) and disturbance regimes. Here, I compare multi-century chronologies of regional fire years and tree recruitment from ponderosa pine forests in the Black Hills of southwestern South Dakota and northeastern Wyoming to reconstructions of precipitation and global circulation indices. Regional fire years were affected by droughts and variations in both Pacific and Atlantic sea surface temperatures. Fires were synchronous with La Niñas, cool phases of the Pacific Decadal Oscillation (PDO), and warm phases of the Atlantic Multidecadal Oscillation (AMO). These quasi-periodic circulation features are associated with drought conditions over much of the western United States. The opposite pattern (El Niño, warm PDO, cool AMO) was associated with fewer fires than expected. Regional tree recruitment largely occurred during wet periods in precipitation reconstructions, with the most abundant recruitment coeval with an extended pluvial from the late 1700s to early 1800s. Widespread even-aged cohorts likely were not the result of large crown fires causing overstory mortality, but rather were caused by optimal climate conditions that contributed to synchronous regional recruitment and longer intervals between surface fires. Synchronous recruitment driven by climate is an example of the Moran effect. The presence of abundant fire-scarred trees in multi-aged stands supports a prevailing historical model for ponderosa pine forests in which recurrent surface fires affected heterogenous forest structure, although the Black Hills apparently had a greater range of fire behavior and resulting forest structure over multi-decadal time scales than ponderosa pine forests of the Southwest that burned more often.

Chronology as Topic↗
PubMed2006

Homeostatic maintenance of ponderosa pine gas exchange in response to stand density changes.

Homeostatic maintenance of gas exchange optimizes carbon gain per water loss. Homeostasis is regulated by short-term physiological and long-term structural mechanisms, both of which may respond to changes in resource availability associated with competition. Therefore, stand density regulation via silvicultural manipulations may facilitate growth and survival through mechanisms operating at both short and long timescales. We investigated the responses of ponderosa pine (Pinus ponderosa) to stand basal area manipulations in Arizona, USA. Stand basal area was manipulated to seven replicated levels in 1962 and was maintained for four decades by decadal thinning. We measured basal area increment (BAI) to assess the response and sustainability of wood growth, carbon isotope discrimination (A) inferred from annual rings to assess the response of crown gas exchange, and ratios of leaf area to sapwood area (A(l):A(s)) to assess longer term structural acclimation. Basal area treatments increased soil water potential (r2 = 0.99) but did not affect photosynthetic capacity. BAI increased within two years of thinning, and the 40-year mean BAI was negatively correlated with stand basal area (r2 = 0.98). delta was negatively correlated with stand basal area for years 5 through 12 after thinning (r2 = 0.90). However, delta was relatively invariant with basal area for the period 13-40 years after initial thinning despite maintenance of treatment basal areas via repeated decadal thinnings. Independent gas exchange measurements verified that the ratio of photosynthesis to stomatal conductance was invariant with basal area, but absolute values of both were elevated at lower basal areas. A(l):A(s) was negatively correlated with basal area (r2 = 0.93). We hypothesize that increased A(l):A(s) is a homeostatic response to increased water availability that maximizes water-use efficiency and whole-tree carbon uptake. Elevated A(l):A(s) of trees at low basal areas was associated with greater resilience to climate, i.e., greater absolute BAI during drought; however, trees with high A(l):A(s) in low basal area stands also exhibited the greatest sensitivity to drought, i.e., greater relative decline in BAI.

Carbon Isotopes↗
PubMed2005

Initial tree establishment on blocky quarry waste ameliorated with hydrogel or slate processing fines.

Pocket planting reclamation techniques developed in the 1970s for revegetating blocky quarrying waste have met with very limited success, often because the low water-holding capacity of the waste and limited root development within a small volume of planting pocket material result in severe drought mortality. We tested pocket planting approaches for waste tip reclamation at Europe's largest slate quarry, and compared materials for enhancing the continuity of water- and nutrient-holding down into the interior of the waste tip. When small compost-filled pocket planting bags were placed above slate processing fines (SPF) or water absorbent cross-linked polyacrylamide gel ("hydrogel"), tree growth rates increased in comparison with pocket planting bags alone. The SPF significantly improved tree survival especially during severe drought, but survival was not enhanced by the use of hydrogel. The sorption characteristics of hydrogel indicated that its presence may help to reduce nutrient leaching, but that it may have a negative effect on nitrogen availability. A more likely explanation for the poor performance of pure hydrogel is that it did not maintain sufficient available water, because of discontinuities caused by shrinkage and movement of the hydrogel, and/or degradation of water-holding capacity with environmental exposure. However, the root growth observed in the hydrogel treatments suggests that this technique, if adapted to reduce the effects of hydrogel shrinkage by using finer-grade hydrogel, mixing it with other soil-forming material, and reducing its exposure to extremes of temperature or sunlight, might have the potential to improve the growth and survival of trees planted on sites where delivery of heavy materials such as SPF is impractical. Fine mineral processing waste is freely available at active quarries and should be seen as a key resource for reclamation schemes.

Conservation of Natural Resources↗
PubMed2002

Water Relations of Standard Height and Dwarf Sunflower Cultivars.

Development of early maturing short stature sunflower (Helianthus annuus L.) cultivars followed the success of semi-dwarf cereals. Although a number of breeding programs have recently released dwarf sunflower cultivars for production in western Canada, the drought adaptability of dwarf cultivars has not been studied. Therefore, field studies were conducted under rainfed conditions at two Manitoba locations during 1994 and 1995 to compare seasonal water relations of 'Sunwheat-103' (SW-103), a dwarf hybrid, and 'AC-Aurora' (Aurora), a dwarf open pollinated cultivar, with 'IS-6111', a standard height hybrid. The dwarf hybrid, SW-103, experienced less stress (up to 0.44 MPa higher leaf water potential) than the standard height hybrid, IS-6111. Genotypic variation for osmotic adjustment was observed in both 1994 and 1995. SW-103 and Aurora respectively had up to 0.42 and 0.39 MPa lower osmotic potential at full turgor compared with IS-6111. Aurora displayed greater osmotic adjustment per unit decrease in leaf water potential than other cultivars. All cultivars maintained positive pressure potential during the study and whenever significant differences in pressure potential were observed, SW-103 usually had higher pressure potential than other cultivars. IS-6111 maintained higher photosynthetic rate and stomatal conductance than the dwarf cultivars. These results suggest that under conditions of adequate water supply, the tall hybrid had the highest productivity despite experiencing the lowest leaf water potential and osmotic adjustment. The drought tolerance advantages of shorter statured cultivars identified here may be more important to productivity maintenance under limited soil water conditions.

Journal Article↗
PubMed1992

Mycotoxins in foods and feeds in the United States.

Mycotoxins are considered unavoidable contaminants in foods and feeds because agronomic technology has not yet advanced to the stage at which preharvest infection of susceptible crops by fungi can be eliminated. The aflatoxins have received greater attention than any of the other mycotoxins because of their demonstrated carcinogenic effects in susceptible animals and their acute toxic effects in humans. Since 1965, the U.S. Food and Drug Administration (FDA) has enforced regulatory limits on the concentrations of these toxins in foods and feeds involved in interstate commerce. The FDA routinely monitors the food and feed industries through compliance programs to ensure that the levels of exposure to these toxins are kept as low as practical. This report summarizes data generated from compliance programs on aflatoxins for the fiscal years 1989, 1990, and the first half of 1991. Commodities sampled included peanuts and peanut products, tree nuts, corn and corn products, cottonseed, and milk. Higher than usual levels of contamination were found in corn examined from all areas of the United States in 1989 as a result of the severe drought that affected the 1988 corn crop. The drought in parts of the South and Southeast in 1990 resulted in increased contamination in corn and peanuts from those areas. A review of the surveillance data obtained on deoxynivalenol, zearalenone, ochratoxin A, sterigmatocystin, penicillic acid, and patulin over the years along with available toxicological data for these mycotoxins indicated that no regulatory actions were warranted. The lack of sufficient surveillance data on other mycotoxins that occur in the United States can be attributed in part to the unavailability of reliable analytical methodology.

Aflatoxins↗
PubMed1991

Effects of additives and growth environment on preservation and digestibility of wheat silage fed to Holstein heifers.

Wheat grown in two separate years under different environmental conditions was fed as silage to investigate effects of additives on forage preservation and digestibility. Direct-cut wheat was harvested in an early head stage of maturity. Wheat was drought stressed in yr 1 and averaged 41.6% DM, and yr 2 averaged 23.0% DM at harvest. Forage was ensiled in 10 900-kg concrete stave silos; 2 per year were assigned to one of five treatments consisting of control, treatment with an enzyme-chemical product, or treatment with one of three different types of lactic acid bacterial inoculants. Each year, during two 12-d periods, forage from five different silos was fed individually for ad libitum intake, separate from concentrate (1.1% of BW) to 15 Holstein heifers (average BW 228 +/- 32 kg). Wheat forage and silage from yr 1 was lower in CP but higher in NDF, ADF, lignin, and starch than that harvested in yr 2. Silage additives decreased DM and NDF recovery in yr 1 and increased DM, NDF, and neutral detergent solubles recovery in yr 2. Additives increased the ratio of lactic to acetic acid and decreased ammonia in silage both years. Additives increased DM and fiber digestibilities of wheat silage-based rations fed to Holstein heifers in yr 2. In vitro digestibility indicated that these improvements were associated with a reduction in the lag phase of forage digestion. The rate of in vitro DM digestibility was positively correlated with silage DM recovery, suggesting an association with nutrient preservation. Wheat preservation and digestibility both were improved by silage additives when wheat was grown under normal environmental conditions, but losses were greater with additives in drought-stressed forage.

Animals↗
PubMedDate not supplied

Factors contributing to the emergence of Escherichia coli O157 in Africa.

In 1992, a large outbreak of bloody diarrhea caused by Escherichia coli O157 infections occurred in southern Africa. In Swaziland, 40,912 physician visits for diarrhea in persons ages >5 years were reported during October through November 1992. This was a sevenfold increase over the same period during 1990-91. The attack rate was 42% among 778 residents we surveyed. Female gender and consuming beef and untreated water were significant risks for illness. E. coli O157:NM was recovered from seven affected foci in Swaziland and South Africa; 27 of 31 patient and environmental isolates had indistinguishable pulsed-field gel electrophoresis patterns. Compared with previous years, a fivefold increase in cattle deaths occurred in October 1992. The first heavy rains fell that same month (36 mm), following 3 months of drought. Drought, carriage of E. coli O157 by cattle, and heavy rains with contamination of surface water appear to be important factors contributing to this outbreak.

Africa, Southern↗
PubMed1976

Schistosomiasis in the Gorgol Valley of Mauritania.

Schistosomiasis may be increasing in West Africa due to the development of water-resource projects which were given a strong impetus by the disastrous Sahelian drought. This report concerns the existing epidemiology of schistosomiasis in West Africa for the Fourth Region of Mauritania, along the Gorgol River. In this area two reservoirs are proposed, to supply a new rice irrigation system. During May and November 1974, field surveys were made to determine the prevalence and intensity of schistosomiasis, and the relevant species of snails. The surveys were made as a basis for designing the irrigation systems to minimize transmission. The only snails found in the area were two species of Bulinus; therefore, the human population was tested for Schistosoma haematobium. A high prevalence of schistosomiasis was found in M'Bout, the town nearest the proposed reservoir at Foum Gleita. Prevalence rates were lowest in Kaedi near the confluence of the Gorgol and Senegal rivers. During the period between the first and second survey the incidence rate among children in M'Bout became very high (68%), probably because of increased water contact related to the rains that broke the long drought in August 1974.

Adolescent↗
PubMed1993

Ross River virus isolations from mosquitoes in arid regions of Western Australia: implication of vertical transmission as a means of persistence of the virus.

Outbreaks of mosquito-borne Ross River (RR) virus disease (epidemic polyarthritis) occur suddenly in the arid north and interior of the State of Western Australia, often within a few weeks of heavy rainfall. Between outbreaks, these regions may undergo long periods of drought, with little or no mosquito or arbovirus activity. The means by which RR virus is reintroduced or reactivated in these areas when environmental conditions favor mosquito-borne virus activity are unknown. In this paper, we describe isolations of RR virus from eight mosquito species trapped at two different locations, one coastal and one inland, in the arid Pilbara region of Western Australia, prior to outbreaks of epidemic polyarthritis. The isolation of RR virus has not been previously reported for five of these species and the isolations from the other three species are new records for Western Australia. The timing and number of isolations of RR virus from Aedes (Ochlerotatus) vigilax (Skuse, 1889) implicate that species as a vector of the virus on the Pilbara coast. Significantly, RR virus was isolated from pools of male Ae. vigilax and male Ae. (Macleaya) tremulus (Theobald, 1903) mosquitoes. This is the first report of RR virus (or other Australian arbovirus) isolates from wild-caught male mosquitoes. Both Ae. vigilax and Ae. tremulus have desiccation-resistant eggs that can survive long periods of drought, making them ideal candidates for the overwintering of arboviruses. The findings implicate vertical transmission as a means of persistence of RR virus in arid regions of Australia and therefore offer a likely explanation for the sudden recurrence of virus activity after heavy rains.

Aedes↗
PubMed1998

Increasing prevalence of canine heartworm in coyotes from California.

Thirty-seven subadult and adult coyotes (Canis latrans), collected August 1992 through December 1996 from a coastal foothill area in northern California (USA), were examined for adult heartworm (Dirofilaria immitis). During 1992 through 1993, at the end of a 6 yr drought, none of four coyotes examined were infected with heartworms. However, during 1994 through 1996, after the drought had ended, prevalences were 91% in 23 adult coyotes and 40% in 10 subadult coyotes. Heartworm intensity did not differ by sex of coyote, and averaged (+/- SE) 19.4 +/- 3.8 among adults; one subadult had > 238 heartworms. The prevalence and intensity of heartworm infection in coyotes reported here for 1994 through 1996 are the highest reported anywhere in the United States.

Animals↗
PubMed2000

Effects of irradiance and spectral quality on leaf structure and function in seedlings of two Southeast Asian Hopea (Dipterocarpaceae) species.

We studied the development of leaf characters in two Southeast Asian dipterocarp forest trees under different photosynthetic photon flux densities (PFD) and spectral qualities (red to far-red, R:FR). The two species, Hopea helferi and H. odorata, are taxonomically closely related but differ in their ecological requirements; H. helferi is more drought tolerant and H. odorata more shade tolerant. Seedlings were grown in replicated shadehouse treatments of differing PFD and R:FR. We measured or calculated (1) leaf and tissue thicknesses; (2) mesophyll parenchyma, air space, and lignified tissue volumes; (3) mesophyll air volumes (V(mes)/A(surf)) and surfaces (A(mes)/A(surf)); (4) palisade cell length and width; (5) chlorophyll/cm and a/b; (6) leaf absorption; and (7) attenuance/absorbance at 652 and 550 nm. These characters varied in response to light conditions in both taxa. Characters were predominantly affected by PFD, and R:FR slightly influenced many characters. Leaf characters of H. odorata were more plastic in response to treatment conditions. Characters were correlated with each other in a complex fashion. Variation in leaf anatomy is most likely a consequence of increasing leaf thickness in both taxa, which may increase mechanical strength and defense against herbivory in more exposed environments. Variation in leaf optical properties was most likely affected by pigment photo-bleaching in treatments of more intense PFD and was not correlated with A(max). The greater plasticity of leaf responses in H. odorata helps explain the acclimation over the range of light conditions encountered by this shade-tolerant taxon. The dense layer of scales on the leaf undersurface and other anatomical characters in H. helferi reduced gas exchange and growth in this drought-tolerant tree.

Journal Article↗
PubMed2000

Theoretical aspects of surface-to-volume ratios and water-storage capacities of succulent shoots.

Surface-to-volume (S/V) ratios of drought-adapted plants affect transpiration, photosynthesis, and water-storage capacity. The S/V ratio of cladodes and flat leaves is S/V = 2/T, where T is thickness: even slight thickening greatly reduces S/V. During rain/drought cycles succulent stems swell and shrink without tearing by having flexible ribs, but ribs increase S/V above that of a smooth cylindrical stem with equal volume: the increased surface area is S(ribbed)/S(cylindrical) = N[x + (π/N)]/π(1 + x), where N is number of ribs and x is rib height relative to the radius of the inner stem. Numerous low ribs provide moderate expandability (storage volume) with little increase in S/V and are adaptive where droughts are short. Tall ribs provide greater expandability but greatly increase S/V and probably are adaptive only in mesic habitats. Having ∼8-15 ribs, each about as tall as the inner stem radius, provides large storage capacity and intermediate increase in S/V. By increasing absolute size, S/V is reduced so greatly that even large ribs can have an S/V smaller than that of a narrow cylindrical or spherical stem with less volume.

Journal Article↗
PubMed2000

Sulpholipid reflects plant resistance to stress-factor action.

The results of studying the behaviour of sulphoquinovosyldiacylglycerol (SQDG) during environmental-factor action are discussed. Low-temperature action caused SQDG accumulation in 1-year-old shoot bark of resistant apple varieties, and was especially striking in the Siberia apple, a variety of extreme hardiness. Another unfavourable factor, high temperature, induced SQDG accumulation in leaves and chloroplasts of drought-resistant plants while in sensitive plants a decrease in its content took place. Water deficit caused the same effect. SQDG increase was also observed in field experiments with artificial irrigation in the drought region of Ukraine, at the stages of stooling and milk ripeness. Besides, SQDG accumulation was observed in wheat plants infected by Puccinia graminis and kidney bean plants infected by tobacco mosaic and potato x viruses. But lead supplied at various concentrations caused an SQDG decrease in wheat seedling leaves and roots. The reasons for these phenomena seemed to be mainly the stabilization of the photosynthetic processes, particularly ATP synthesis and light-harvesting complex II functioning, but signal function also cannot be excluded.

Agriculture↗
PubMed2001

Leaf ureide degradation and N(2) fixation tolerance to water deficit in soybean.

Accumulation of ureides in leaves is associated with the sensitivity of N(2) fixation in soybean to soil water deficit. Consequently, ureide degradation in leaves may be a key to increasing soybean tolerance to dry soils. Previous research indicated that allantoic acid degradation is catalysed by different enzymes in cultivars Maple Arrow and Williams. The enzyme found in Williams requires manganese as a cofactor. The first objective of this study was to determine if the two degradation pathways were associated with differences in N(2) sensitivity to soil water deficits. N(2) fixation of Williams grown on low-Mn soil was sensitive to stress, but it was relatively tolerant when grown on soil amended with Mn. N(2) fixation in Maple Arrow was relatively tolerant of soil drying regardless of the Mn treatment. The second objective of this study was to expand the study of the degradation pathway to nine additional genotypes. Based on ureide degradation in the presence and absence of Mn, these genotypes also segregated for the two degradation pathways. Those genotypes with the Mn-dependent pathway tended to have drought-sensitive N(2) fixation, but there was one exception. The genotypes not requiring Mn for ureide degradation were drought-tolerant except for one genotype. These results demonstrated the possibility for increasing N(2) fixation tolerance to soil water deficits in soybean by selection of lines with high ureide degradation rates, which were commonly associated with the Mn-independent pathway.

Allantoin↗