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In this study we used the cuttings of Populus przewalskii Maximowicz as experimental material and sodium nitroprusside (SNP) as nitric oxide (NO) donor to determine the physiological and biochemical responses to drought stress and the effect of NO on drought tolerance in woody plants. The results indicated that drought stress not only significantly decreased biomass production, but also significantly increased hydrogen peroxide content and caused oxidative stress to lipids and proteins assessed by the increase in malondialdehyde and total carbonyl contents, respectively. The cuttings of P. przewalskii accumulated many amino acids for osmotic adjustment to lower water potential, and activated the antioxidant enzymes such as superoxide dismutase, guaiacol peroxidase and ascorbate peroxidase to maintain the balance of generation and quenching of reactive oxygen species. Moreover, exogenous SNP application significantly heightened the growth performance of P. przewalskii cuttings under drought treatment by promotion of proline accumulation and activation of antioxidant enzyme activities, while under well-watered treatment the effect of SNP application was very little.
Comparative study of microfossils from two kinds of sediments: chert intercalations (studied in thin section) and phosphorite/phosphatic carbonate (in thin section and maceration), from the upper Neoproterozoic Doushantuo phosphorites in the Weng’an area, Guizhou Province, South China, shows that the phosphatized Megasphaera ornata and the chert−preserved Tianzhushania tuberifera should be regarded as representing the same taxon preserved by different mineralization processes. In phosphatized specimens the outer wall is often peeled off, exposing the ornamented middle wall. Some phosphatized specimens isolated from the rock matrix and specimens seen in thin sections of phosphorites show a partly preserved outer wall with spines, which can be compared to the thin−sectioned specimens from the chert beds. The small pits usually seen on the surface of the ornamented middle wall of phosphatized specimens correspond to the attachment spots of the spines in the outer wall. The presence of a spiny outer wall is a characteristic of Tianzhushania Yin and Li, 1978. Tianzhushania ornata (Xiao and Knoll, 2000) comb. nov. is here proposed as the valid name for the species. The proposed resting−egg nature of T. ornata, mainly based on the ornament type of the middle wall, cannot be excluded. The presence of a spiny outer wall, however, suggests that it is a pelagic rather than a benthic form.
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