Taxanes content and cytotoxicity of hazel cells extract after elicitation with silver nanoparticles.

The toxicity of silver nanoparticles (AgNPs) has been attributed to the generation of Ag+ ions as well as production of ROS. The latter can elicit defensive response of plant cells in different ways e.g., enhancement of secondary metabolite productions. In the present study this hypothesis was evaluated by assessment of taxanes production by suspension-cultured hazel (Corylus avellana L.) cells after treatment with AgNPs. The cells were treated with different concentrations of AgNPs (0, 2.5, 5, and 10 ppm), in their logarithmic growth phase (d7) and were harvested after 1 weak. The growth of cells and their membrane integrity decreased but extracellular electro conductivity and total dissolved solids increase by AgNPs (probably due to loosening of cell membrane). Treatment of hazel cells with AgNPs (in particular of 5 ppm) rapidly and remarkably increased the yields of two major taxanes, i.e., Taxol and baccatin III; so that 24 h of the treatment their contents reached to 378% and 163% of the control, respectively. Increase of Taxanes was accompanied by the increase of total soluble phenols. The extracts of AgNPs-treated cells were able to inhibit the growth of cancerous HeLa cells and reduce their viability to 60% of the control. The results suggest the elicitation of suspension-cultured hazel cells with AgNPs as a procedure for rapid enhancement of anticancer taxanes biosynthesis by the cells.

Chloroplast DNA phylogeography of Betula maximowicziana, a long-lived pioneer tree species and noble hardwood in Japan.

Betula maximowicziana is an ecologically and economically important tree species in Japan. In order to examine the phylogeographical pattern of the species in detail, maternally inherited chloroplast (cp) DNA variations of 25 natural populations of Betula maximowicziana and a total of 12 populations of three related species were evaluated by PCR-RFLP analysis. Two main haplotypic groups of B. maximowicziana populations (northern and southern) were detected, with the main boundary passing through the Tohoku region in northeastern Japan; in addition there was high genetic differentiation among the 25 populations studied (GST = 0.950, G'ST =0:977). The phylogeographical pattern exhibited by B. maximowicziana was much more similar to that of alpine plants than to that of beech and oak. Comparison of the patterns of genetic structure obtained from the cpDNA with previously and newly acquired data on bi-parentally inherited nuclear DNA indicates that the nuclear genome was transferred via pollen from the northern haplotypic group to the southern group more frequently than it moved in the opposite direction. Although common haplotypes were detected among B. maximowicziana and the two related species examined, these haplotypes were not shared sympatrically, suggesting very rare hybridization among the species currently occurring in their natural populations.

Interspecific variation in nighttime transpiration and stomatal conductance in a mixed New England deciduous forest.

Transpiration is generally assumed to be insignificant at night when stomata close in response to the lack of photosynthetically active radiation. However, there is increasing evidence that the stomata of some species remain open at night, which would allow for nighttime transpiration if there were a sufficient environmental driving force. We examined nighttime water use in co-occurring species in a mixed deciduous stand at Harvard Forest, MA, using whole-tree and leaf-level measurements. Diurnal whole-tree water use was monitored continuously with Granier-style sap flux sensors in paper birch (Betula papyrifera Marsh.), red oak (Quercus rubra L.) and red maple (Acer rubrum L.). An analysis was conducted in which nighttime water flux could be partitioned between refilling of internal water stores and transpiration. Substantial nighttime sap flux was observed in all species and much of this flux was attributed to the refilling of depleted water stores. However, in paper birch, nighttime sap flux frequently exceeded recharge estimates. Over 10% of the total daily sap flux during the growing season was due to transpiration at night in paper birch. Nighttime sap flux was over 8% of the total daily flux in red oak and 2% in red maple; however, this flux was mainly associated with recharge. On nights with elevated vapor pressure deficit, sap flux continued through the night in paper birch, whereas it reached zero during the night in red oak and red maple. Measurements of leaf-level gas exchange on a night with elevated vapor pressure deficit showed stomatal conductance dropping by only 25% in paper birch, while approaching zero in red oak and red maple. The study highlighted differences in ecophysiological controls on sap flux exerted by co-occurring species. Paper birch is a fast-growing, shade-intolerant species with an earlier successional status than red oak and red maple. Risking water loss through nighttime transpiration may provide paper birch with an ecological advantage by enabling the species to maximize photosynthesis and support rapid growth. Nighttime transpiration may also be a mechanism for delivering oxygen to respiring cells in the deep sapwood of paper birch.