Numbers of desquamated epithelial cells, yeast cells and bacterial organisms were counted in samples collected from the external ear canal of 37 normal dogs and 16 normal cats, and from 24 dogs and 22 cats with otitis externa. The aims of the study were to establish quantitative reference ranges and to correlate these data with the clinical status of the dogs and cats. Numbers of yeast cells and bacterial organisms were significantly increased in dogs (P = 0.05; P = 0.0001) and cats (P = 0.0001; P = 0.0001) with otitis externa, and in most cases high counts were correlated with clinical signs. Mean Malassezia counts per high-power dry field of > or = 5 in the dog and > or = 12 in the cat were considered abnormal. Mean bacterial counts per high-power dry field of > or = 25 in the dog and > or = 15 in the cat were considered abnormal. When used to differentiate normal from inflamed external ear canals, these figures provided a low sensitivity but a specificity of > or = 95%.

The redox and acidlbase states and midpoint potentials of cytochrome b-559 have been determined in oxygenevolving photosystem I1 (PS 11) particles at room temperature in the pH range from 6.5 to 8.5. At pH 7.5 the fresh PS I1 particles present about 213 of their cytochrome b-559 in its reduced and protonated (non-autooxidizable) high-potential form and about 1/3 in its oxidized and non-protonated low-potential form. Potentiometric reductive titration shows that the protonated high-potential couple is pH-independent (Eo, + 380 mV), whereas the low-potential couple is non-protonated and pH-independent above pH 7.6 (Eo, pH > 7.6, + 140 mV), but becomes pH-dependent below this pH, with a slope of -72 mV/pH unit. Moreover, evidence is presented that in PS I1 particles cytochrome b-559 can cycle, according to its established redox and acidlbase properties, as an energy transducer at two alternate midpoint potentials and at two alternate pKa values. Red light absorbed by PS I1 induces reduction of cytochrome b-559 in these particles at room temperature, the reaction being completely blocked by dichlorophenyldimethylurea.The location and function of cytochrome b-559 in the chloroplast electron-transport chain(s), although widely and intensively investigated, have remained enigmatic and controversial [l -81. Understanding the oxidation/reduction potential and pH dependence of this cytochrome in high-potential (HP) low-potential (LP) forms is essential for assessing its role as both an electron carrier and a proton carrier, but in this regard the literature is ambiguous and includes incomplete and contradictory data. Equally important is deciding whether cytochrome b-559 is reduced or oxidized by light absorbed by photosystem 11, since the reported results are also contradictory in this respect. [15] this effect, which is reversible upon raising the pH, is inhibited by 3-(3',4'-dichloropheny1)-1,l'-dimethylurea (+ 395 mV at pH 7.8; + 335 mV at pH 5.0, and + 380 mV at pH 5.0 and in the presence of dichlorophenyldimethylurea). More recently our group [19 -211 obtained solid evidence that in spinach thylakoids the HP couple of cytochrome b-559 is pH-independent in the pH range between 6.5 and 8.5 (Eb, + 340 mV), whereas the LP couple is pH-independent above pH 7.6 (Eo, pH > 7.6, + 75 mV), but becomes pH-dependent below this pH, with a slope of -60 mV/pH unit. According to our proposal [6,21] the cytochrome functions at low potential as electron acceptor of PS 11, and at high potential as electron donor to PS I, thus acting as a transducer of redox energy into acidlbase energy between the two photosystems.The HP form of cytochrome b-559 is labile towards treatments, such as aging, sonication, mild heating, incubation in Tris buffer or Triton X-100, addition of either carbonylcyanide p-trifluoromethoxyphenylhydrazone or carbonylcyanide 3-chlorophenylhydrazone (CCCP), trypsin digestion, NaCl washing, that may alter or disrupt membrane structure and that cause what is usually considered an 'irreversible' conversion to the LP fo...

Iron limitation is the major factor controlling phytoplankton growth in vast regions of the contemporary oceans. In this study, a combination of thermoluminescence (TL), chlorophyll fluorescence, and P700 absorbance measurements have been used to elucidate the effects of iron deficiency in the photosynthetic electron transport of the marine diatom P. tricornutum. TL was used to determine the effects of iron deficiency on photosystem II (PSII) activity. Excitation of iron-replete P. tricornutum cells with single turn-over flashes induced the appearance of TL glow curves with two components with different peaks of temperature and contributions to the total signal intensity: the B band (23°C, 63%), and the AG band (40°C, 37%). Iron limitation did not significantly alter these bands, but induced a decrease of the total TL signal. Far red excitation did not increase the amount of the AG band in iron-limited cells, as observed for iron-replete cells. The effect of iron deficiency on the photosystem I (PSI) activity was also examined by measuring the changes in P700 redox state during illumination. The electron donation to PSI was substantially reduced in iron-deficient cells. This could be related with the important decline on cytochrome c6 content observed in these cells. Iron deficiency also induced a marked increase in light sensitivity in P. tricornutum cells. A drastic increase in the level of peroxidation of chloroplast lipids was detected in iron-deficient cells even when grown under standard conditions at low light intensity. Illumination with a light intensity of 300 μE m-2 s-1 during different time periods caused a dramatic disappearance in TL signal in cells grown under low iron concentration, this treatment not affecting to the signal in iron-replete cells. The results of this work suggest that iron deficiency induces partial blocking of the electron transfer between PSII and PSI, due to a lower concentration of the electron donor cytochrome c6. This decreased electron transfer may induce the over-reduction of the plastoquinone pool and consequently the appearance of acceptor side photoinhibition in PSII even at low light intensities. The functionality of chlororespiratory electron transfer pathway under iron restricted conditions is also discussed.