High Osmotic Strength Research Articles

Regulation of Photosynthetic Electron Transport in Intact Spinach Chloroplasts

Relatively high concentrations of monovalent salts (150 millimolar) stimulated light-saturated uncoupled rates of O(2) evolution linked to oxaloacetic acid (OAA) reduction by intact chloroplasts 2-to 3-fold. In contrast, monovalent salts partially inhibited light-saturated rates of O(2) evolution coupled to CO(2) fixation and uncoupled rates of nitrite reduction. In the presence of high salt concentration, light-saturated rates of electron transport were about equivalent for all three terminal electron acceptors. It is inferred that exogenous monovalent salts have at least two effects on photosynthetic electron transport, independent of photophosphorylation and CO(2) metabolism: a partial inhibitory effect common to OAA, NO(2) (-) and CO(2) reduction and a marked stimulatory effect unique to the photoreduction of OAA.The stimulation of electron transport to OAA was effected by certain exogenous monovalent salts (KCl or NaCl, but not LiCl). Divalent salts (MgCl(2) or CaCl(2)) and high osmotic strength were ineffective. The salt-induced stimulation was eliminated by low concentrations of phosphate or sulfate (>/= millimolar) and by higher concentrations of magnesium (>/=30 millimolar). These results suggest that the ion content of the medium (or cytosol) is potentially important in modulating photosynthetic electron transport events in intact chloroplasts.

Systemic and ocular mechanisms of anuran adaptation to altered environments: Effects on electrolyte and urea concentrations in plasma and aqueous humor

Osmotically stressed toads have high levels of circulating urea that could pose a significant problem in the secretion of isosmotic aqueous humor. This question was studied in toads ( Bufo marinus) adapted for 30 days in (1) 5 mosmol artificial pond water, (2) 155 mosmol saline or (3) 330 mosmol Ringer's solution. The Na + and Cl − concentrations in plasma and aqueous humor rose significantly in osmotically stressed animals but did not in animals adapted to 5 mosmol environments. The concentration of K + did not change significantly. The urea concentration did not increase in animals adapted to 155 mosmol saline; however, toads adapted to 330 mosmol Ringer's solution did show an eightfold increase, to 62 m m, in both plasma and aqueous humor. Unlike mammals, the toads did not show a significant difference in urea concentration between plasma and AH. Therefore, urea may penetrate the blood-aqueous barrier by means of a special transport mechanism. This hypothesis was tested by comparing the [ 14C]urea rate of entry into aqueous humor to the rates of entry of the related solutes [ 14C]thiourea and [ 14C]acetamide. The transport constant for [ 14C]urea (0·023 min −1) was four to nine times that of [ 14C]thiourea, a solute which is 13 times more lipid soluble than urea. Adaptation to environments of high osmotic strength did not affect the rate of transport of either solute. [ 14C]acetamide, a solute which is larger than thiourea and less lipid soluble, entered aqueous humor at three to seven times the rate of [ 14C]thiourea. These results indicated that urea and acetamide crossed the blood-aqueous barrier by a mechanism predominantly apart from simple diffusion, i.e. the transport of urea into aqueous humor of the toad was facilitated.

Studies on Lettuce Seed Quality: I. Effect of Seed Size and Weight on Vigor

Abstract In the paper by O. E. Smith, N. C. Welch, and T. M. Little in J. Amer. Soc. Hort Sci. 98(6):529-533, November 1973, the following changes should be made on page 529, column 2, lines 28 and 35: Line 28: change “transferred to a 1/15 M” to read “transferred to a 20-fold dilution of a 1/15 M” Line 35: change “of the pH 7.0 phosphate” to read “of the pH 7.0 dilute phosphate” If the buffer is used at 1/15 molar, the roots of the young plants will be injured due to the high osmotic strength of the buffer.

The cell wall of Escherichia coli: early effects of penicillin treatment and deprivation of diaminopimelic acid.

SUMMARY: The morphological effects on bacterial walls of the early stages of inhibition of mucopolymer synthesis have been investigated in Escherichia coli. Inhibition was achieved in strain B by penicillin treatment and in auxotrophic strains M203 and M173-25 by deprivation of diaminopimelic acid (DAP). Only growing organisms were affected; the walls of organisms in stationary phase remained unchanged. The first effects of treatment with penicillin appear in 20 min., whereas changes in DAP-deprived auxotrophs become visible only after 40-60 min. The soft layers of the wall formed bag-like protrusions and, at the same time, wide gaps or holes developed in the proteinaceous portion of the rigid layer. Widening of these gaps was paralleled by a weakening of the rigid layer, resulting eventually in bursting of the cell, or in protective media of high osmotic strength, in the formation of spheroplasts. The initial appearance and the subsequent widening of gaps in the rigid layer, observed almost exclusively in organisms multiplying logarithmically, are taken to indicate the presence of a mechanically weak mucopolymer formed under conditions that prevent crosslinking. The discontinuities, interpreted as sites of mucopolymer synthesis, were randomly distributed over the bacterium. Their appearance at the poles of the bacteria seemed frequently to be suppressed by media of high osmotic pressure, in which plasmolysis was first seen in the polar regions. The observations suggest that morphogenesis of the protein layer is dependent on the secondary structure of the mucopolymer in newly synthesized wall areas.