Morphological characteristics of ripples are analyzed considering bed surfaces as two dimensional random fields of bed elevations. Two equilibrium phases are analyzed with respect to successive development of ripples based on digital elevation models. The key findings relate to the shape of the two dimensional second-order structure functions and multiscaling behavior revealed by higher-order structure functions. Our results suggest that (1) the two dimensional second-order structure functions can be used to differentiate the two equilibrium phases of ripples; and (2) in contrast to the elevational time series of ripples that exhibit significant multiscaling behavior, the DEMs of ripples at both equilibrium phases do not exhibit multiscaling behavior.
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.
Seedlings of winter rape were cultured in vitro on media containing 24-epibrassinolide, EBR (100 nM) and cadmium (300 µM). After 14 d of growth, fast fluorescence kinetics of chlorophyll (Chl) a and contents of photosynthetic pigments and Cd in cotyledons were measured. Cd was strongly accumulated but its content in cotyledons was 14.7 % smaller in the presence of EBR. Neither Cd nor EBR influenced the contents of Chl a and b and carotenoids. Cd lowered the specific energy fluxes per excited cross section (CS) of cotyledon. The number of active reaction centres (RC) of photosystem 2 (RC/CS) decreased by about 21.0 % and the transport of photosynthetic electrons (ET0/CS) by about 17.1 %. Simultaneously, under the influence of Cd, the activity of O2 evolving centres (OEC) diminished by about 19.5 % and energy dissipation (DI0/CS) increased by about 14.6 %. In the cotyledons of seedlings grown on media without Cd, EBR induced only a small increase in the activity of most photochemical reactions per CS. However, EBR strongly affected seedlings cultured with cadmium. Specific energy fluxes TR0/CS and ET0/CS of the cotyledons of plants Cd+EBR media were about 10.9 and 20.9 % higher, respectively, than values obtained for plants grown with Cd only. EBR also limited the increase of DI0/CS induced by Cd and simultaneously protected the complex of OEC against a decrease of activity. Hence EBR reduces the toxic effect of Cd on photochemical processes by diminishing the damage of photochemical RCs and OECs as well as maintaining efficient photosynthetic electron transport. and A. Janeczko ... [et al.].
Floristic composition, morphological functional types and habitat distributions for C4 species were studied in Xinjiang, North-western China. 89 species, in 9 families and 41 genera, were identified with C4 photosynthesis. 48 % of these C4 species were found in Monocotyledoneae, e.g. Cyperaceae (5 species), Gramineae (38 species), the other 52 % was in Dicotyledoneae, e.g. Chenopodiaceae (29 species), Amaranthaceae (7 species), and Polygonaceae (5 species). Compared with those in semi-arid grasslands in North China and tropical forests in South China, more plant families were found with the occurrence of C4 plants in this arid region. Relatively higher annual species (63 %), shrubs (18 %), and Chenopodiaceae C4 species (33 %) compositions were the primary characteristics for the C4 species occurring in Xinjiang, and this was remarkably related with its arid environment. More Chenopodiaceae C4 species occurring in the region suggested that this type of C4 species may have higher capacity to fit the air and soil droughts. There was a strong relationship between C4 occurrence and habitat distributions, more than half of the total 89 C4 species were found in disturbed and cultivated lands and early stages of vegetation successions, indicating C4 occurrence was not only related with climate changes, but also with land uses and vegetation dynamics.