A new nematode species, Philometroides caudata sp.n., is described from the swimbladder (under the serosa cover) of the freshwater pimelodid catfish, Rhamdia guatemalensis, from cenotes (— sinkholes) in Yucatan, southeastern Mexico. It differs from all hitherto known members of the genus, except P. maplestoni (Travassos, Artigas et Pereira, 1928), in having the functional anus, the conical tail with a terminal knob-like structure and the oesophagus without an anterior inflation in female, and in the structure of the caudal end in male. It can be distinguished from P. maplestoni (described only from females) by the extent of embossed cuticle, the size of body and the host type. P. caudata, representing a Neotropical element, is the first Philometroides species reported from freshwater fishes in Mexico.
Phosphotylatíon of some polypeptides of photosystem 2 (PS2) core was observed for chloroplasts phosphoiylated under anaerobic conditions. These polypeptides appeared in the photosystem 1 (PSI) paiticles isolated from phosphorylated chloroplasts. Phosphorylated PS2 was transferred onto PSI as an integrál complex, which retained photochemical activity and originated variable fluorescence.
The activities of the whole chain electron transport and photosystems 1 and 2 in isolated chloroplasts of Sesuvium poríulacastrum L. (a halophytic herb) increased with concentrations of NaCl (100 to 600 mM), and declined at high NaCl concentrations (600 to 900 mM).
Chloroplasts isolated from the primary leaves of wheat seedlings lost 22 % of their chlorophyll and 35 % of the carotenoids after 4 h of incubation under a medium irradiance (MI) (400 pmol m'^ s'*, PAR). After a 3 h MI exposure, the photosystem (PS) 2 activity was completely lost while photosystem 1 (PSI) activity was reduced to 32 % of that, found initially. Chloroplasts isolated from the leaves of seedlings exposed to a high irradiance (1500 pmol m-^ s"') contained a higher concentiation of zeaxanthin (z) and lost pigments and photochemical activities at a relatively slower rate. When the z concentration in chloroplasts incubated under MI was enhanced several times by ascorbate (Asc), the losses of pigment contents and photosystem activities were significantly reduced. However, when the Asc-induced synthesis of z was inhibited by dithiothreitol, protection of the pigment contents and photochemical activities disappeared. Thus, z can photoprotect the chloroplasts during incubation under irradiation.
The possibility of simultaneously ušed chlorophyll (Chl) synthesis precursor (glutamic acid) and metal chelator (2,2'-dipyridyl) as a photodynamic inhibitor of the chlorophyll synthesis was studied. Wheat {Triticum aestivum L.) and vegetable marrow {Cucurbita moschata Duch.) leaves were treated with 2,2'-dipyridyl (2,2'- DP), and 2,2'-DP along with glutamic acid which increased the protochlorophyllide (Pchlide) content in the vegetable marrow plants to a higher extent. An irradiation of the treated leaves caused an inhibition of Pchlide reduction which was more notable in those of the dicotyledonous vegetable marrow plant.
The preparation of Dl/D2/cytochrome 6559 complex isolated from pea (Pisum sativum h.) was photoinactivated by "white light" (140 W m‘2) at 20 and 4 "C in both the presence and absence of oxygen. The inactivation was followed by measuring the decline of the photoinduced absorbance change A/4683 (the photoaccumulation of reduced pheophytin), by measuring absorption spectra and fluorescence emission, and by polypeptide analysis. In the presence of oxygen, the ability of the DUDUcyi 6559 complex to acciunulate reduced pheophytin was lost with the halftime im of about 3 min and fluorescence quantum yield declined with ti/2 of about 30 min at both 20 and 4 ^C. The D\ and Dl polypeptides were rapidly modified at 20 °C as reflected by the presence of their large aggregates at the start of the electrophoretic gel and by a decrease of the mobility of remaining Dl and Dl monomers. This modification was substantially limited at 4 “C. Subímits of cytochrome 6559 were not modified at any temperature. When oxygen was removed, the halftime of the A/1683 decline increased by about one order of magnitude, fluorescence emission did not decline, but slightly increased, and the polypeptide pattem was only slightly affected during irradiation.
Primary events in the photoinactivation of photosystem (PS) 2 membrane fragments by low and high "visible light" irradiance (17 to 1 700 W m'2) and UV-B irradiation (90 W m'2) were analyzed by measuiing flash-induced absorption changes at 830 nm that reflect transient formation of P680+ and Pheo*. Following results were obtained: (7) Irradiation with "visible light" under aerobic conditions affects the PS 2 electron transfer at two different sites: {a) within the PS 2 reaction centre by impairment of primary charge separation (P680 Pheo Qa P680+Pheo'QA), and (7>) on tiie PS 2 donor side by inhibition of the electron transfer from to P680+. (2) In PS 2 membrane fragments with intact 02-evolution the primary charge separation is the most sensitive target of the photoinhibition by "visible light". The UV-B irradiation, however, affects predominantly the oxygen-evolving complex or the electron transfer from the oxygen-evolving complex to Yz®’'. (5) Susceptibility of the P680 Yz segment to photoinhibition by "visible light" is drastically increased in the samples with lifetimes of Yz°* and P680+ having been signifícantly prolonged by Tris- treatment. Susceptibility of the primaiy charge separation to photoinhibition, however, is not dependent on the lifetimes of P680+ and Yz®’'.
Immunological quantification of the thylakoid membranes Dl protein showed that in intact leaves of spinách and intact mesophyli protoplasts of Valerianella locusta L. photoinactivation of photosystem 2 was not related to the net degradation of Dl. The data indicate a sync^onization between the Dl degradation and resynthesis during photoinhibition and recovery in vivo.
Photoinhibitory fluorescence quenching, qjjj, was detected in šitu in a montane spruce forest using a non-destructive chloropbyll fluorescence method combined with parallel sampling of light and temperature data. occuired as a common phenomenon in this type of ecosystem, altbougb low irradiances (LI) were tfae major factor limiting the growth. Under the prevailing LI photoinhibition was due to the suboptimal temperatures rather than irradiance. The found pattem of photoinhibitory fluorescence quenching is supposed to be characteristic of measuring sites in this montane region, where high irradiance (HT) is rare, but if it occurs, then it is along with a high temperature.