The same amount of water has been present on our planet for about 4 billion years, since shortly after the Earth was formed. Since then it has cycled through evaporation, condensation, precipitation and surface runoff multiple times. Water scarcity as an abiotic factor ranging from moderate to severe stress levels, accompanied by loss of moisture in the soil, is extremely hard for most organisms to cope with, particularly terrestrial plants and their food-chain dependents.
Vitamin E Deficiency: Treatment
Symptomatic vitamin E deficiency should be treated with 800–1200 mg of αtocopherol per day. Patients with abetalipoproteinemia may need as much as 5000–7000 mg/d. Children with symptomatic vitamin E deficiency should be treated with 400 mg/d orally of water-miscible esters; alternatively, 2 mg/kg per d may be administered intramuscularly. Vitamin E in high doses may protect against oxygen-induced retrolental fibroplasia and bronchopulmonary dysplasia, as well as intraventricular hemorrhage of prematurity.
Decreased aldosterone synthesis may be due to primary adrenal insufficiency (Addison's disease) or congenital adrenal enzyme deficiency (Chap. 336). Heparin (including low-molecular-weight heparin) inhibits production of aldosterone by the cells of the zona glomerulosa and can lead to severe hyperkalemia in a subset of patients with underlying renal disease, diabetes mellitus, or those receiving K+-sparing diuretics, ACE inhibitors, or NSAIDs.
Metabolic acidoses, with the exception of those due to the accumulation of organic anions, can be associated with mild hyperkalemia resulting from intracellular buffering of H+ (see above). Insulin deficiency and hypertonicity (e.g., hyperglycemia) promote K+ shift from the ICF to the ECF. The severity of exercise-induced hyperkalemia is related to the degree of exertion. It is due to release of K+ from muscles and is usually rapidly reversible, often associated with rebound hypokalemia.
Biotin is a water-soluble vitamin that plays a role in gene expression, gluconeogenesis, and fatty acid synthesis and serves as a CO 2 carrier on the surface of both cytosolic and mitochondrial carboxylase enzymes. The vitamin also functions in the catabolism of specific amino acids (e.g., leucine). Excellent food sources of biotin include organ meat such as liver or kidney, soy, beans, yeast, and egg yolks; however, egg white contains the protein avidin, which strongly binds the vitamin and reduces its bioavailability.
IN BOTH NATURAL AND AGRICULTURAL CONDITIONS, plants are frequently exposed to environmental stresses. Some environmental factors, such as air temperature, can become stressful in just a few minutes; others, such as soil water content, may take days to weeks, and factors such as soil mineral deficiencies can take months to become stressful. It has been estimated that because of stress resulting from climatic and soil conditions (abiotic factors) that are suboptimal, the yield of field-grown crops in the United States is only 22% of the genetic potential yield (Boyer 1982).
Moisture deficiencies occurring early in the crop cycle
may delay the maturity season and reduce yields.
Shortages later in the season often lower quality, as
well as yields. However, irrigation surplus, especially
late in the season, can reduce both the quality and the
post-harvest life of the crop.
Uneven or surplus irrigation, above the amount
required to replace evapotranspiration, causes nitrate
leaching below the root system and the ability of
the crop to recover from the nitrogen deficiency
There were conflicting requirements in the data given in these
documents, and a number of decisions had to be made on the basis
of experience of the members of the Ergonomics Unit and
consultation with oth er ergonomists.
The Australian Standard listed above had only just been published
at the start of the development of the checklists. While this
standard provides a useful starting point for a designer, it has some
deficiencies which should be eliminated in future revisions.
Table 73-8 Selected Metabolic Disturbances and Their Correction
Corrective Action with PN
water or decreased total body water sodium sodium
Occurs commonly with
or water to produce net
hypertonic fluid followed by positive fluid balance diuretic administration with maintaining sodium
free water clearance; can also and chloride balance occur with dehydration and normal total body sodium
Inadequate relative to need
The GM2-activator protein (GM2AP) is an essential cofactor for the lyso-somal degradation of ganglioside GM2 by b-hexosaminidase A (HexA). It
mediates the interaction between the water-soluble exohydrolase and its
membrane-embedded glycolipid substrate at the lipid–water interface.
Functional deficiencies in this protein result in a fatal neurological storage
disorder, the AB variant of GM2 gangliosidosis.
The purpose of irrigation is to prevent water stress,
especially during the formation of the part of the plant
that will be harvested.
Water stress can occur in a crop when the soil
moisture is excessive or when it’s deficient. When
oxygen concentration levels in the soil atmosphere are
lowered due to displacement by water for an extended
period of time, the root system can be severely
Lettuce and green-leaf plants are especially susceptible
to water stress due to their shallow root systems.
Most foods contain some folate. The highest concentrations are found in liver, yeast, spinach, other greens, and nuts (100 µg/100 g). The total folate content of an average Western diet is ~250 µg daily, but the amount varies widely according to the type of food eaten and the method of cooking. Folate is easily destroyed by heating, particularly in large volumes of water. Total-body folate in the adult is ~10 mg, the liver containing the largest store. Daily adult requirements are ~100 µg, so stores are only sufficient for 3–4 months in normal adults and severe folate deficiency may...