Alterations of chemical composition, construction cost and payback time in needles of Masson pine (Pinus massoniana L.) trees grown under pollution.

Previous studies show that Masson pine (Pinus massoniana L.) stands grown at the industrially-polluted site have experienced unprecedented growth decline, but the causal mechanisms are poorly understood. In this study, to understand the mechanisms of growth decline of Mason pine strands under pollution stresses, we determined the reactive oxygen species levels and chemical composition of the current-year (C) and one-year-old (C + 1) needles, and calculated the needle construction costs (CCmass) of Masson pine trees grown at an industrially-polluted site and an unpolluted remote site. Pine trees grown at the polluted site had significantly higher levels of hydroxyl radical and superoxide anion in their needles than those grown at the unpolluted site, and the former trees eventually exhibited needle early senescence. The contents of lipids, soluble phenolics and lignins in C and C + 1 needles were significantly higher at the polluted site than at the unpolluted site, but the total amounts of non-construction carbohydrates were lower in non-polluted needles than in polluted needles. Elevated levels of the reactive oxygen species and early senescence in polluted needles together led to significant increases in CCmass and a longer payback time. We infer that the lengthened payback time and needle early senescence under pollution stress may reduce the Masson pine tree growth and consequently accelerate tree decline.

Antioxidant enzymes regulate reactive oxygen species during pod elongation in Pisum sativum and Brassica chinensis.

Previous research has focused on the involvement of reactive oxygen species (ROS) in cell wall loosening and cell extension in plant vegetative growth, but few studies have investigated ROS functions specifically in plant reproductive organs. In this study, ROS levels and antioxidant enzyme activities were assessed in Pisum sativum and Brassica chinensis pods at five developmental stages. In juvenile pods, the high levels of O2.- and .OH indicates that they had functions in cell wall loosening and cell elongation. In later developmental stages, high levels of .OH were also related to increases in cell wall thickness in lignified tissues. Throughout pod development, most of the O2.- was detected on plasma membranes of parenchyma cells and outer epidermis cells of the mesocarp, while most of the H2O2 was detected on plasma membranes of most cells throughout the mesocarp. This suggests that these sites are presumably the locations of ROS generation. The antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) apparently contributed to ROS accumulation in pod wall tissues. Furthermore, specifically SOD and POD were found to be associated with pod growth through the regulation of ROS generation and transformation. Throughout pod development, O2.- decreases were associated with increased SOD activity, while changes in H2O2 accumulation were associated with changes in CAT and POD activities. Additionally, high POD activity may contribute to the generation of(.)OH in the early development of pods. It is concluded that the ROS are produced in different sites of plasma membranes with the regulation of antioxidant enzymes, and that substantial ROS generation and accumulation are evident in cell elongation and cell wall loosening in pod wall cells.

More nitrogen partition in structural proteins and decreased photosynthetic nitrogen-use efficiency of Pinus massoniana under in situ polluted stress.

Masson pine (Pinus massoniana L.) trees in the Pearl River Delta have shown growth decline since late 1980s, particularly those around industrially polluted regions. As nitrogen is an important nutritional element composing functional proteins, structural proteins and photosynthetic machinery, investigation on nitrogen allocation is helpful to understand nutrient alteration and its regulation mechanism in response to pollution stress. Current year (C) and 1-year old needles (C + 1) of five mature trees were sampled in industrially polluted site and unpolluted natural reserve for bioassay. Needles of declining trees had significantly higher leaf nitrogen per unit area (N(L)) but lower photosynthetic capacity (P (max)), which resulted in lower photosynthetic nitrogen use efficiency (PNUE) than those of healthy trees. Nitrogen fraction to the photosynthetic apparatus in the C and C + 1 needles at polluted site was 27 and 22%, significantly lower than the corresponding healthy needles (48 and 32%). The content of structural proteins was positively correlated with N(L) in C and C + 1 needles. Moreover, the C and C + 1 needles of declining trees had about 1.8 times structural protein as those of healthy trees, suggesting that more nitrogen allocation to structural protein are needed for stronger structural defenses under polluted stress. Decreases in PNUE of declining pine trees could be partially explained by increases in structural protein nitrogen.

Light acclimation and HSO(3) (-) damage on photosynthetic apparatus of three subtropical forest species.

The effects of long-term (33 months) sun/shade acclimation and short-term (within 10 h) HSO(3) (-) treatment on leaf photosynthetic apparatus were investigated in three subtropical forest plants, Pinus massoniana, Schima superba, and Acmena acuminatissima. After 33 months' growth in two light environments (100 and 12% sunlight), rapid light curves (RLC), chlorophyll fluorescence imaging and chloroplast ultrastructures of three tested species were changed to different degrees. When leaf sections were immersed in 50 mM NaHSO(3) for 10 h, all the RLCs were lowered; chlorophyll fluorescence imaging was inclined to present warmer colors and imaging areas were decreased. However, changes in chloroplast ultrastructures differed from three species. Our results showed that the photosynthetic apparatus of a dominant species, A. acuminatissima, in the late succession stage of a subtropical forest in South China, was less sensitive to NaHSO(3) under both growing light intensities. Conversely, the chloroplasts of P. massoniana, the pioneer heliophyte species, were most susceptible to NaHSO(3). It is deduced that, SO(2) pollution may become as a factor to accelerate the succession of subtropical forest.