Gendi Xu

Effects of nano-TiO2 on photosynthetic characteristics of Ulmus elongata seedlings

The physiological and ecological responses of Ulmus elongata to different concentrations of nano-anatase TiO2 solutions were investigated in this study and we found that with foliar application of 0.1% (T1), 0.2% (T2) and 0.4% (T3) nano-anatase TiO2 solution the net photosynthetic rate of U. elongata seedlings were lower, comparing with the control (CK) (no spraying). TiO2 solution had no effect on the carbon isotope values (δ(13)C), indicating the lower photosynthetic capacity was not caused by stomatal limitation. The nitrogen isotope values (δ(15)N) decreased, but the foliar metal elements, such as Mg, K and Mn contents were not affected by nano-anatase TiO2 which promoted the Cu uptake. Fourier transform infrared spectroscopy showed that the nano-anatase TiO2 enhanced the absorbance of U. elongata leaves, especially for 1064, 1638, 2926 and 3386 cm(-1) bands, indicating the synthesis of carbohydrate and lipid compounds was a kind of mechanism under the toxic effects of nanonanoparticles.

Effect of toxic Fe2+ levels on the biological characteristics of rice root border cells

Root border cells are a population of rhizosphere cells surrounding the root tips but separated from them. The root tip is a major target of Fe2+ toxicity; thus, it was hypothesized that the border cells might protect or exacerbate Fe2+ toxicity. To explore the effects of excess Fe2+ on the border cells in rice (Oryza sativa L.), experiments were carried out using the border cells in vitro (Shanyou No. 10). The border cells were precultured under “hanging in the air” and detached from the root tips. The shape, numbers, and viability of border cells were examined during exposure to toxic levels of Fe2+. When the root was 1 mm long, there were 205 border cells on average. With the growth of the root, more border cells were observed. When the root grew to 25 mm long, the total number of border cells reached a maximum, while the maximum activity of border cells appeared when the root was 20 mm long. The pectin methyl esterase (PME) activity of the root cap peaked at a root length of 2 mm. Border cell development was related to PME activity in rice. Excessive Fe2+ was toxic to detached border cells. After treatment with 200 μM Fe2+ solution for 48 h, cell viability decreased by 72.70%. However, when treated with 400 μM Fe2+ solution, the number of viable cells was actually higher, suggesting the induction of a cellular self-protection response. The activity of PME first increased under high concentrations of Fe2+ and then decreased. These results indicate that toxic levels of Fe2+ modulate PME activity and border cell survival.

Significance of Stump-Sprouting for the Population Size Structure and Spatial Distribution Patterns of Endangered Species, Magnolia cylindrical

ABSTRACT Magnolia cylindrica Wils. is one of the third most-protected wild plants in China. To describe the size structure and dynamics of its population, field data were obtained from eight newly established sites, using a contiguous grid quadrate method in Jiulong Mountain of East China. The population size structure and spatial distribution pattern were discussed based on a theoretical distribution model and assembling intensity index. The population size structure showed a declining trend because of the lack of seedlings. The number of stump-sprouting, size class III (sapling trees) individuals was large enough to make up for the shortage of small seedlings and the complete regeneration of populations through sprouting. The distributions of M. cylindrica, both seedling populations (Group A) and overall populations (Group B), were mostly clumped. The spatial pattern intensities of the populations at different stages (mainly small trees, middle trees, and big trees) were higher for Group A than those for Group B. The two groups have the same tendency in that the pattern intensity declined from small trees to the larger ones. Group A and Group B differed in spatial pattern: small and middle trees were randomly distributed in seedling populations, but aggregated in overall populations. The populations of M. cylindrica (both group A and B) were characterized by the pattern scale between 16 to 32 m2, measured by Greig-Smith and Kershaw methods. These results suggest that sprouting should be seriously considered in population rehabilitation and forest tending management and the area of forest tending management should be close to the maximum intensity.

Effects of iron toxicity on the morphological and biological characteristics of rice root border cells

ABSTRACT Toxicity of Fe2+ is one of the major constraints for lowland rice production in tropical and subtropical areas. The root tip is a primary site of iron (Fe2+) toxicity in rice. To explore the effects of iron toxicity on the morphological and biological characteristics on the border cells in rice (Oryza sativa L.), experiments were carried out using the border cells in two cultivars. The experimental results revealed the following properties of border cells shared by both rice cultivars: the first border cells appeared almost synchronously with the emergence of the primary root tip; the number of border cells reached maximum when the root was 25 mm long; the border cells were most viable when the root length was 20 mm; and the relative activity of pectin methylesterase (PME) was the highest when the root length was 2 mm. The two rice cultivars exhibited different trends in their response to Fe2+ toxicity: the number of root border cells in Fe2+-resistant Zhongyou 9288 increased when experiencing low levels of Fe2+ treatment, but then declined at higher Fe2+ levels. The number of root border cells in Fe2+-sensitive Shanyou No. 10, however, declined rapidly when the concentration of Fe2+ increased. The results also showed that Fe2+ toxicity hindered the development of root border cells of both rice cultivars, but the Fe2+ sensitive variety experienced thickened the root cap cell walls that led to programmed cell death.