The physiological light response of two tree species across a hydrologic gradient in Brazilian savanna (Cerrado)

Tropical savanna ecosystems are extremely diverse and important for global carbon storage. In the state of Mato Grosso, tropical savanna (locally known as the Cerrado), turns from well-drained, upland areas into seasonally flooded areas within the Pantanal; however, the Cerrado and the Pantanal share many common tree species, such as Vochysia divergens, a flood-adapted tree native to the Amazon Basin, and Curatella americana, a tree, adapted native to the welldrained the Cerrado. We measured the photosynthetic light response of these species in the the Cerrado and the Pantanal over a 1-year period to determine how these species physiologically adjust to these hydrologically distinct habitats. We hypothesized that neither species would experience a significant decline in maximum, light-saturated photosynthetic rate (P _max) in their naturalized habitat. Physiological performance of each species was generally higher in the habitat that they were adapted to; however, our data indicated that both species have broad tolerance for seasonal variations in hydrology, allowing them to tolerate seasonal drought during the dry season in the Cerrado, and seasonal flooding during the wet season in the Pantanal. In V. divergens, flexible water-use efficiency, higher specific leaf area (SLA), and a greater ability to adjust mass-based P _max (P _max,m) to variations in leaf N and P concentration appeared to be key traits for withstanding prolonged drought in the Cerrado. In C. americana, increases in SLA and higher nutrient-use efficiency appeared to be important in maintaining high rates of P _max,m in the seasonally flooded Pantanal. Flexibility in physiology and resource-use efficiency may allow these species to survive and persist in habitats with broadly differing hydrology.     

Analysis of tissue chimerism in nude mouse brain and abdominal xenograft models of human glioblastoma multiforme: what does it tell us about the models and about glioblastoma biology and therapy?

In situ hybridization coupled to immunohistochemistry for antigens of interest allows unequivocal identification of tumor cells from reactive stroma cells and normal adjacent structures in human glioblastoma multiforme grafts transplanted into nude mice. With this methodology, we have explored the development of glioblastoma multiforme solid grafts transplanted into nude mouse brains or flanks. The brain transplants closely resembled the human situation, particularly in relation to differentiation and growth patterns. The morphological features of peritumoral reactive gliosis were similar to those observed in humans. A mouse glial stroma within the main tumor masses was also demonstrated. Kinetic studies showed that the compartment of isolated tumor cells that infiltrated host brains and the reactive gliosis constituted two cycling cell populations. Despite VEGF protein expression by tumor cells and some reactive astrocytes, the abnormally permeable microvascular beds were not hyperplastic. The observation of a non-infiltrative pattern of growth when grafts were established in host flanks demonstrated that the organ-specific environment plays a determining role in the growth and invasive properties of glioblastoma. The phylogenetic distance between man and mouse and the recipient immunoincompetence should not impose serious limitations on the use of this model for studying malignant glioma biology and therapy in vivo.