Bleaching herbicide effects on plastids of dark-grown plants: lipid composition of etioplasts in amitrole and norflurazon-treated barley leaves

The effects of the bleaching herbicides amitrole (125 micro M) and norflurazon (100 micro M) on etioplast lipids were studied in barley plants (Hordeum vulgare L. cv. Express) grown for 7 d either at 20 degrees C or 30 degrees C in darkness. Total lipid, glycolipid and phospholipid contents of control etioplasts were increased at 30 degrees C in comparison with those at 20 degrees C. The two herbicides caused a decrease in the total lipid, glycolipid and phospholipid amounts compared to the untreated etioplasts and lowered the lipid to protein ratio. In the controls, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) accounted for about 66 mol% of the etioplast polar lipids, while the remainder was represented by sulphoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG), in approximately equal proportions. Both amitrole and norflurazon increased MGDG at both temperatures, but decreased DGDG except with norflurazon at 30 degrees C. As a consequence, the MGDG to DGDG molar ratio was higher in the herbicide-treated etioplasts compared to the controls at both the growth temperatures. The amount of the negatively charged polar lipids SQDG and PG were decreased by treatments with amitrole at 20 degrees C and norflurazon at 30 degrees C. The two herbicides determined different responses in the fatty acid unsaturation of the individual polar lipids. Changes in the lipid composition of etioplasts and the interaction between the pigment-protein complex, protochlorophyllide-NADPH-protochlorophyllide oxidoreductase, and polar lipids are discussed.     

The spermatozoon of arthropoda. XXV. A new model of tail having up to 170 doublets: Monarthropalpus buxi

The spermatozoon of M. buxi which belongs to the Cecidomyiidae family have been studied. The spermatozoa have an aberrant flagellum somewhat similar to that of Sciaridae formed by about 170 doublets ranged in rows to form a compact bundle. Accessory tubules and all the other axonemal structures are missing. The sperm is characterized by the lack of acrosome, and by the presence of normal mitochondria apically gathered before the nucleus.     

Responses of the Populus × euramericana clone I-214 to excess zinc: Carbon assimilation,structural modifications,metal distribution and cellular localization

Poplar (Populus), the model system in tree research, is a fast-growing and high biomass plant which is promising for energy, paper and pulp production, and for growth in soils contaminated with metals. Contamination of soils and water with heavy metals has become a widespread problem; environmental pollution by excess zinc (Zn), one of the more important contaminants, occurs frequently and yet the responses of Populus to high Zn concentrations are still not clearly understood.We investigated the effects of Zn on the functional and structural parameters in the Populus × euramericana clone I-214 by Zn localization in frozen-hydrated leaves and roots by cryo-scanning electron microscopy (cryo-SEM)/energy-dispersive X-ray microanalysis (EDXMA). The experiment was conducted on cuttings grown in nutrient solutions with an increasing Zn concentration gradient (0.001–10 mM).Biomass partitioning and Zn uptake were affected by the metal treatments, showing organ- and tissue-dependent responses. In particular, Zn accumulated in old leaves and moved from shoot to root as the Zn concentration in the growth medium increased. At the highest treatment concentration (10 mM), Zn was preferentially localized in photosynthetic tissues of shoots, and in epidermis and cortex tissues of roots. Gas exchange and chlorophyll measurements showed impairments in leaf biochemistry rather than in stomatal function. Modifications in foliage area, stomatal density and leaf layer thickness were investigated to reduce and/or compensate the negative effects of excess Zn on CO₂ assimilation.To counteract Zn toxicity, clone I-214 adopted different defense/tolerance mechanisms involving complex structural, physiological and biochemical processes, attributed to both Zn excluders and accumulators. This study demonstrates the advantages of combining cryo-SEM/EDXMA, gas exchange and chemical analyses for studying metal localization and structural as well as physiological responses in plants.     

Seawater irrigation: antioxidant defence responses in leaves and roots of a sunflower (Helianthus annuus L.) ecotype

Salinity is a widespread environmental stress for crop plants. It is common in arid, semiarid, and coast regions. In those environments, seawater infiltrations can occur or the sea provides the only source of water for irrigation. The effects of 10% and 20% seawater in nutrient solutions were studied in 30 day-old plants of sunflower (Helianthus annuus L.) ecotype Katharina Piacenza. Growth parameters, ascorbate and glutathione contents, and the activities of ascorbate peroxidase and glutathione reductase were determined in shoots and roots. The results showed antioxidative responses of the ecotype to both salt treatments. The different activity patterns of antioxidant molecules and enzymes in the leaves and roots suggested a different kind of reaction to the two seawater concentrations.