Carbohydrate storage in wood and bark of rubber trees submitted to different level of C demand induced by latex tapping.

When the current level of carbohydrates produced by photosynthesis is not enough to meet the C demand for maintenance, growth or metabolism, trees use stored carbohydrates. In rubber trees (Hevea brasiliensis Muell. Arg.), however, a previous study (Silpi U., A. Lacointe, P. Kasemsap, S. Thanisawanyangkura, P. Chantuma, E. Gohet, N. Musigamart, A. Clement, T. Améglio and P. Thaler. 2007. Carbohydrate reserves as a competing sink: evidence from tapping the rubber tree. Tree Physiol. 27:881-889) showed that the additional sink created by latex tapping results not in a decrease, but in an increase in the non-structural carbohydrate (NSC) storage in trunk wood. In this study, the response of NSC storage to latex tapping was further investigated to better understand the trade-off between latex regeneration, biomass and storage. Three tapping systems were compared to the untapped Control for 2 years. Soluble sugars and starch were analyzed in bark and wood on both sides of the trunk, from 50 to 200 cm from the ground. The results confirmed over the 2 years that tapped trees stored more NSC, mainly starch, than untapped Control. Moreover, a double cut alternative tapping system, which produced a higher latex yield than conventional systems, led to even higher NSC concentrations. In all tapped trees, the increase in storage occurred together with a reduction in trunk radial growth. This was interpreted as a shift in carbon allocation toward the creation of reserves, at the expense of growth, to cover the increased risk induced by tapping (repeated wounding and loss of C in latex). Starch was lower in bark than in wood, whereas it was the contrary for soluble sugars. The resulting NSC was twice as low and less variable in bark than in wood. Although latex regeneration occurs in the bark, changes related to latex tapping were more marked in wood than in bark. From seasonal dynamics and differences between the two sides of the trunk in response to tapping, we concluded that starch in wood behaved as the long-term reserve compartment at the whole trunk level, whereas starch in bark was a local buffer. Soluble sugars behaved like an intermediate, ready-to-use compartment in both wood and bark. Finally, the dynamics of carbohydrate reserves appears a relevant parameter to assess the long-term performance of latex tapping systems.

Carbohydrate reserves as a competing sink: evidence from tapping rubber trees.

Carbohydrate reserve storage in trees is usually considered a passive function, essentially buffering temporary discrepancies between carbon availability and demand in the annual cycle. Recently, however, the concept has emerged that storage might be a process that competes with other active sinks for assimilate. We tested the validity of this concept in Hevea brasiliensis Müll. Arg. (rubber) trees, a species in which carbon availability can be manipulated by tapping, which induces latex regeneration, a high carbon-cost activity. The annual dynamics of carbohydrate reserves were followed during three situations of decreasing carbon availability: control (no tapping), tapped and tapped with Ethephon stimulation. In untapped control trees, starch and sucrose were the main carbohydrate compounds. Total nonstructural carbohydrates (TNC), particularly starch, were depleted following bud break and re-foliation, resulting in an acropetal gradient of decreasing starch concentration in the stem wood. During the vegetative season, TNC concentration increased. At the end of the vegetative season, there were almost no differences in TNC concentration along the trunk. In tapped trees, the vertical gradient of starch concentration was locally disturbed by the presence of the tapping cut. However, the main effect of tapping was a dramatic increase in TNC concentration, particularly starch, throughout the trunk and in the root. The difference in TNC concentration between tapped and untapped trees was highest when latex production was highest (October); the difference was noticeable even in areas of the trees that are unlikely to be directly involved in latex regeneration, and it was enhanced by Ethephon stimulation, which is known to increase latex metabolism and flow duration. Thus, contrary to what could be expected if reserves serve as a passive buffer, a decrease in carbohydrate availability resulted in a net increase in carbohydrate reserves at the trunk scale. Such behavior supports the view that trees tend to adjust the amount of carbohydrate reserves stored to the level of metabolic demand, at the possible expense of growth.

Taking treatment decisions in non-melanoma skin cancer--the place for topical photodynamic therapy (PDT).

BACKGROUND: Epithelial non-melanoma skin cancer (NMSC) like actinic keratosis (AK), Bowen's disease (BD) and basal cell carcinoma (BCC) represent the most common malignancies in the fair skinned population. Epidemiological data reveal high incidences, especially for actinic keratoses, which are basically non-invasive squamous cell carcinomas, but fortunately bear a low risk of mortality for a single lesion. Nevertheless these lesions should be generally treated if other factors such as the state of the patient indicate that this is appropriate. The appearance of new treatment modalities like immuno-modulating topical agents, topical diclofenac, and photodynamic therapy in addition to a long list of already established treatments (curettage, surgery, cryotherapy, topical 5-fluorouracil, and many others) have led to the fact that patients and treating physicians have a large spectrum of therapeutic options to choose from. The same--with some variations--holds true for Bowen's disease and BCC. METHODS: Aim of this article is to offer an overview over NMSCs and their treatment options with emphasis on photodynamic therapy (PDT) as classical indications for PDT, to provide resources for guidelines for the treatment of these diseases, and to position PDT in this context by helping selecting patients that would profit most from topical PDT. RESULTS: Sufficient evidence is available to regard PDT as a standard treatment modality for NMSC. In addition to randomized controlled trials, long-term experience helps to find out the most appropriate treatment modality in a given patient. CONCLUSION: Physicians treating NMSC should have access to PDT and be trained and experienced in its use.