Effects of flooding under hydrostatic pressure on the respiratory metabolism of germinated wheat seeds

Germinated wheat seeds ( Triticum aestivum L. cv. Barqai) that had been subjected to short hydrostatic pressure treatments (0.3–1.2 MPa) changed their normal metabolism into one which is characterized by a high ethanol production, a low O₂ consumption and a low CO₂ evolution. Alcoholic fermentation could account for ca half of the CO₂ evolved from the pressurized seeds. The level of acetaldehyde was low, though significantly higher in the pressurized seeds than in the controls. Subjection of wheat seeds to osmotic stress under aerobic conditions lowered their O₂ uptake and CO₂ evolution but did not induce ethanol production. Exposure of pressurized seeds to NaCl stress did not alter their ethanol production beyond that which had been induced by pressure. Ethanol production by pressurized seeds increased following either the addition of sucrose or by excision of the embryos from the endosperms. More electrolytes leaked into the embedding solution from pressurized seeds than from control seeds. Exogenous ethanol was toxic to wheat seeds at concentrations as low as 343 m M . The effects of hydrostatic pressure and of the consequently induced ethanol production on the mortality of flooded seeds is discussed.     

Relation of phospholipase D activity to the decay of succinate dehydrogenase and of covalently bound flavin in yeast cells undergoing glucose repression

The disappearance of succinate dehydrogenase activity and of protein-bound histidyl flavin were studied in aerobic yeast cells incubated with high glucose concentrations. The decay of succinate dehydrogenase activity, covalently bound flavin, and of respiration is prevented by cycloheximide but not by chloramphenicol. During this decay there is a large increase in mitochondrial phospholipase D activity; the appearance of this enzyme is also prevented by cycloheximide. It seems possible, therefore, that the formation of phospholipase D may be important in triggering the disappearance of covalently bound flavin, succinate dehydrogenase, and of other mitochondrial enzymes during glucose repression of aerobic yeast cells.     

The effect of salinity on glucose absorption and incorporation by pea roots

Osmotic adaptation was observed in pea plants grown in Na₂SO₄salinized media but no complete adaptation was observed in plantsgrown in NaCl salinized media. The absorption of externally supplied glucose was depressedin pea root tips from plants grown in media salinized with eitherNaCl or Na₂SO₄. Under NaCl salinity this depression increasedwith increasing salinity. Under Na₂SO₄ salinity, no significantinhibition of absorption was observed in roots exposed to waterpotentials higher than –5 atmosphere. The amount of ¹⁴Creleased as CO₂, expressed as the percent of absorbed ¹⁴C, increasedwith increasing salinity of both types. In roots grown underNaCl salinity, the incorporation of ¹⁴C into ethanol non-soluble,acid hydrolyzable substances was markedly inhibited. This inhibitionwas increased by increasing the external salinity. The effectof Na₂SO₄ salinity was similar but not so pronounced. The incorporation of ¹⁴C from externally supplied glucose intothe alkali-soluble fraction was practically uneffected by salinity.Non-extractable ¹⁴C was decreased in roots exposed to NaCl butwas not, apparently, effected by Na₂SO₄). Because of the smallnessof this fraction no clear cut conclusion can be made. Possiblemechanisms for the events are discussed. (Received October 26, 1972; )     

Tropomyosin isoforms: divining rods for actin cytoskeleton function

Actin filament functional diversity is paralleled by variation in the composition of isoforms of tropomyosin in these filaments. Although the role of tropomyosin is well understood in skeletal muscle, where it regulates the actin-myosin interaction, its role in the cytoskeleton has been obscure. The intracellular sorting of tropomyosin isoforms indicated a role in spatial specialization of actin filament function. Genetic manipulation and protein chemistry studies have confirmed that these isoforms are functionally distinct. Tropomyosins differ in their recruitment of myosin motors and their interaction with actin filament regulators such as ADF-cofilin. Tropomyosin isoforms have therefore provided a powerful mechanism to diversify actin filament function in different intracellular compartments.     

Chytridiomycosis Survey in Wild and Captive Mexican Amphibians

Mexico, a rich country in terms of amphibian diversity, hosts about 375 described species. Population declines have been documented for several species where it is evident that their habitat is being destroyed or modified. However, other species which inhabit pristine areas are declining as well. It has been suggested that the chytrid fungus Batrachochytrium dendrobatidis (B.d.) may be one of the causes of the enigmatic declines in Mexico. We surveyed a total of 45 localities, in 12 states across Mexico, examining a total of 360 specimens representing 14 genera and 30 species. We also examined 91 specimens of Ambystoma mexicanum from a captive population in Mexico City as well as one Pachymedusa dacnicolor obtained in a pet shop. We used a two-tiered technique to detect the pathogen. For wild-caught specimens, we utilized light microscopy to identify presence of B.d. sporangia in amphibian skin. Then, to verify the infection, we used a quantitative real-time PCR assay on collected skin sections which is specific for B.d. For captive animals, we used a nonlethal version of the real-time PCR technique. We found evidence of B.d. infection in 111 animals comprising 14 species in 13 localities. A large percentage (84%) of Ambystoma mexicanum from the colony were infected with B.d. The two most highly infected individuals were the endangered Ambystoma mexicanum, from a captive colony, and Pachymedusa dacnicolor, purchased at a pet shop. The online version of this article (doi:) contains electronic supplementary material, which is available to authorized users.     

Aging alters the metabolic flux signature of the ER‐unfolded protein response in vivo in mice

Age is a risk factor for numerous diseases, including neurodegenerative diseases, cancers, and diabetes. Loss of protein homeostasis is a central hallmark of aging. Activation of the endoplasmic reticulum unfolded protein response (UPR^ER) includes changes in protein translation and membrane lipid synthesis. Using stable isotope labeling, a flux “signature” of the UPR^ER in vivo in mouse liver was developed by inducing ER stress with tunicamycin and measuring rates of both proteome‐wide translation and de novo lipogenesis. Several changes in protein synthesis across ontologies were noted with age, including a more dramatic suppression of translation under ER stress in aged mice as compared with young mice. Binding immunoglobulin protein (BiP) synthesis rates and mRNA levels were increased more in aged than young mice. De novo lipogenesis rates decreased under ER stress conditions in aged mice, including both triglyceride and phospholipid fractions. In young mice, a significant reduction was seen only in the triglyceride fraction. These data indicate that aged mice have an exaggerated metabolic flux response to ER stress, which may indicate that aging renders the UPR^ER less effective in resolving proteotoxic stress.