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The research presented in this study aimed to document the variability of synthetic lead antimonate pigments known as Naples yellow in selected artworks by Czech landscape painters from the turn of the 20th century. Spectra obtained through Raman spectroscopy show considerable difference in the position of main band maximum (from 110 to 145 cm−1) characteristic of cubic pyrochlore structure Pb2Sb2O7—the major phase of the Naples yellow pigment. In several samples, hexagonal PbSb2O6 with main band at 655 cm−1 was identified as a dominant phase, a finding that is somewhat surprising because PbSb2O6 has been generally considered a minor admixture to cubic Pb2Sb2O7. Reference pigment samples were synthesised under known conditions, and their spectra were collected in order to get more comparative material. Also, commercially available Naples yellow pigments were characterised in the same way. We observed considerable differences of the obtained spectra caused by the presence of admixtures and diverse production conditions. The diversity of Naples yellow and the corresponding Raman spectra makes their identification problematic. Presented data thus may serve as a reference material in the identification process. [ABSTRACT FROM AUTHOR]

Cultivars of maize ( Zea mays L.) with different sensitivity to drought were exposed to 0.3 mol/L sorbitol (-1.4 MPa water potential) for 24 h. Exposure to water deficiency significantly reduced the growth of both shoots (coleoptile and hypocotyl) and roots. Shoot growth was inhibited more than the growth of roots. Osmotic stress enhanced accumulation of soluble sugars. Electrolyte leakage, a cell injury index, was slightly increased after 0.3 mol/L sorbitol. Respiration was measured in the presence and absence of 2,6-dichlorophenol indophenol. 2, 6-Dichlorophenol indophenol did not influence respiration rates, because statistically equal results were observed under both conditions. Total respiration (vT) decreased after osmoticum treatment. There were no significant differences in the vT among the cultivars analysed. The decrease in vT was caused by a decline in the activities and capacities of both cytochrome (vcyt, Vcyt) and alternative pathway (valt, Valt) of respiration. A high residual respiration (vres) was observed, up to 27% of total uninhibited respiration. The result of uncoupler use clearly indicated that coupling was maintained after 24 h of osmotic stress. The recovery of the respiration rate was comparable with that of non-stressed control rates. According to these observations, no possible mitochondrial damage is expected. Water deficiency did not induce a stimulation of the alternative oxidase, so we assume that the stimulation of the alternative pathway is not related to drought stress resistance; rather, the function of the alternative pathway is to balance carbon metabolism and electron transport in a response to a changing environment. (Managing editor: Ping He) [ABSTRACT FROM AUTHOR]

Summary • The dynamics of silica deposition and Si aggregates formation in inner tangential walls of root endodermal cells, which occurs as an additional stage of endodermal development in sorghum (Sorghum bicolor ), were studied. • An environmental scanning electron microscope (ESEM) and X-ray microanalyzer (EDAX) were used to study sorghum roots grown hydroponically with Si (+ Si medium) and without Si (– Si medium). • Silica aggregates were absent in roots of plants cultivated in – Si medium. However, their additional formation on fully mature and thickened endodermal cell walls took place when plants grown in – Si medium were transferred to + Si medium. The beginning of Si aggregates formation was observed and Si deposition detected 2 h after transfer to + Si medium. • By dipping the apical root half in + Si medium, the silica aggregates were formed in the endodermis at the basal part of the root. This supports the hypothesis of outward Si transport from the xylem to the endodermis rather than radial inward Si movement and its deposition at the point of the apoplastic barrier represented by the endodermis. [ABSTRACT FROM AUTHOR]

Sorghum belongs to a group of economically important, silicon accumulating plants. X-ray microanalysis coupled with environmental scanning electron microscopy (ESEM) of fresh root endodermal and leaf epidermal samples confirms histological and cultivar specificity of silicification. In sorghum roots, silicon is accumulated mostly in endodermal cells. Specialized silica aggregates are formed predominantly in a single row in the form of wall outgrowths on the inner tangential endodermal walls. The density of silica aggregates per square mm of inner tangential endodermal cell wall is around 2700 and there is no significant difference in the cultivars with different content of silicon in roots. In the leaf epidermis, silicon deposits were present in the outer walls of all cells, with the highest concentration in specialized idioblasts termed ‘silica cells’. These cells are dumb-bell shaped in sorghum. In both the root endodermis and leaf epidermis, silicification was higher in a drought tolerant cultivar Gadambalia compared with drought sensitive cultivar Tabat. Silicon content per dry mass was higher in leaves than in roots in both cultivars. The values for cv. Gadambalia in roots and leaves are 3.5 and 4.1% Si, respectively, and for cv. Tabat 2.2 and 3.3%. However, based on X-ray microanalysis the amount of Si deposited in endodermal cell walls in drought tolerant cultivar (unlike the drought susceptible cultivar) is higher than that deposited in the leaf epidermis. The high root endodermal silicification might be related to a higher drought resistance. [ABSTRACT FROM AUTHOR]