The pH-dependent quenching of chlorophyll (Chl) fluorescence (the high energy quenching) was characterized by stationary Chl-a-fluorescence in the thylakoid membranes and photosystem (PS) 2 preparations. The variable part of fluorescence was quenched, when the pH in the thylakoid lumen decreased below 5.5, i.e., at high ApH. This quenching was caused by an inhibition of electron donation from the manganese cluster to the reaction centre of PS 2. The pH response of quenching suggested that a 1 H'''-transition with an apparent pK of 4.7 was involved. Parallel to quenching at low pH, a Ca^‘'‘-release was measured (1 Ca^'*' per 200 Chl). When the ApH relaxed and the pH on the lumen side increased again, fluorescence recovered provided Ca^'*' was present (Kd = 100 pM). Both the quenching at low pH and the reactivation at pH > 5.5 are light-dependent processes. In the presence of high concentration of extemal Ca^"^, fluorescence recovered even at low pH. Inhibition of the donor-side of PS 2 directly affected the acceptor-side of PS 2, as seen by a shift of the redox potential of Qa from -120 mV (pH 7.0) to +40 mV (pH 4.2). We propose that at high ApH (7) the water splitting side is inactivated by release of Ca from a high afflnity binding site, and (2) Qa is converted to a high-potential form. Excitatíon energy is then dissipated at the PS 2 reaction centres by a recombination reaction between donor and acceptor side. As a result, Qa (and the intersystem electron transport chain) remains oxidized, even in the excessive light.
Java citronella suffers from chlorosis of the younger leaves, particularly in tropical climatic conditions. An Fe-efFicient genotype of this species was grown in Solutions containing 0 to 44.80 g(Fe) m'^ in controlled glasshouse conditions. In comparison with normál Fe nutrition (5.60 g m"^), low (0 - 1.40 g m'^) or high (22.40 - 44,80 g m*^) iron nutrition influenced fresh and dry matter yield, plant height, total essential oil and citronellol contents, chlorophyll (Chl) content, net photosynthetic and transpiration rates, and Fe uptake. Largest differences were found in saccharide and Chl a and h contents and Chl a/h ratio, and stomatal resistance. Significarít positive correlations were observed between fresh matter, citronellol content, dry and fresh matter yields and total essential oil content.
Air-grown tobacco (Nicotiana tabacum L.) plants were transferred for one week into a low oxygen atmosphere (2 kPa O2, LO) to study both immediate and long-term effects of the suppression of photorespiration on net photosynthetic rate (PN), plant morphology, and chloroplast ultrastructure. The PN and the leaf conductance for CO2 increased upon exposure of attached tobacco leaves to LO. These results may suggest that under LO, external CO2 is used to consume the radiant energy normally utilized in photorespiration by net CO2 assimilation at the expense of an increased rate of transpiration. The increase in the coefficient of nonphotochemical fluorescence quenching indicates that under LO, (surplus) radiant energy is also dissipated as heat. Prolonged LO-treatment of tobacco resulted in a decrease in the PN (measured in air) and in a reduction in the number of starch grains in the chloroplasts. Concomitantly, large lipid globuli appeared in the chloroplasts and the distance between the thylakoids forming the grana decreased. These changes in the ultrastructure of chloroplasts may have contributed to the decline in the PN. The LO-treated plants were considerably smaller than the control plants maintained in air. This appears to have resulted from a reduction in the rate of leaf area expansion at the expense of an increase in the specific mass of the leaves. This long-term response to LO-treatment may allow the plants to conserve water. and A. Migge ... [et al.].
Species of Rhamnocercinae Monaco, Wood et Mizelle, 1954 are gill parasites of sciaenid fishes (Perciformes). Seven are marine species (three in the western Atlantic and four in oriental Pacific) and one is a neotropical freshwater species (Rio Doce Basin, Brazil). While the status of the subfamily may be questioned, this assemblage of species is apparently supported by several shared apomorphic and plesiomorphic characters, such as: (1) peduncular spines with anterior and posterior roots; (2) haptor laterally expanded, armed with anchors (two pairs); bars (one ventral, two dorsal); 14 hooks and haptoral accessory spines; and (3) double (nested) tubes of the male copulatory organ (MCO), directed posteriorly with the genital pore lying posterior to the MCO. The phylogenetic hypothesis for the eight known species of this clade is: (Spinomatrix penteormos (Rhamnocercoides stichospinus, Rhamnocercoides menticirrhi) Rhamnocercus oliveri (Rhamnocercus rhamnocercus (Rhamnocercus stelliferi, Rhamnocercus bairdiella, Rhamnocercus margaritae)). This hypothesis indicates that Spinomatrix penteormos represents the sister group of all remaining rhamnocercines. The resulting phylogenetic sister-group relationships support the transfer of Rhamnocercus stichospinus Seamster et Wood, 1956 to Rhamnocercoides Luque et Iannacone, 1991 as Rhamnocercoides stichospinus (Seamster et Wood, 1956) n. comb.
Two wheat {Triticum aestivum L.) cultivars, Trakia (drought-sensitive, DS) and Slavianka 196 (drought-tolerant, DT), were subjected to water stress induced by polyethyleneglycol (PEG) 6000; 15 % PEG for 6 h (mild stress); 25 % PEG for 6 h and 15 % PEG for 24 h (severe stress). Exposure of plants to water stress led to a noticeable decrease in both the initial slope of net photosynthetic rate to intercellular CO2 concentration {Pfilc^ curves and the maximum P-^. Ribulose 1,5-bisphosphate carboxylase (RuBPC) activity was almost unchanged under mild stress while under severe stress it was reduced by about 26-27 %. The ratio of variable to maximal chlorophyll fluorescence did not change which implied that there was little effect of examined stress conditions on the photosystem 2 electron transport. The relative magnitude of stomatal and nonstomatal factors in limitation of photosynthesis depended on stress severity.
Extrasporogonic stages of Sphaerospora sp. from the kidneys of Atlantic salmon (Salmo salar L.) were successfully transmitted via intra-peritoneal injection to naive Atlantic salmon and brown trout (Salmo trutta L.). Rainbow trout (Oncorhynchus mykiss Walbaum) could not be infected in this way. Transmitted extrasporogonic stages continued their development to form sporogonie stages and mature spores in the kidney tubules. Extrasporogonic stages, sporogonie stages and mature spores of the parasite in both experimentally infected hosts were morphologically identical to the equivalent stage in naturally infected Atlantic salmon, although minor differences were seen in spore dimensions. A farm-based exposure experiment confirmed the susceptibility of brown trout to the salmon Sphaerospora, These results are consistent with the view that the salmon Sphaerospora is Sphaerospora truttae Fischer-Scherl, El-Matbouli et Hoffmann, 1986. The parasite is redescribed according to the guidelines of Lom and Arthur (1989) since details of extrasporogonie stages, the ultrastructure of extrasporogonic and sporogonie stage development, and of the parasite’s epidemiology are known from Atlantic salmon but not from other reports.