Immunocytochemical determination of the subcellular distribution of ascorbate in plants

Ascorbate is an important antioxidant in plants and fulfills many functions related to plant defense, redox signaling and modulation of gene expression. We have analyzed the subcellular distribution of reduced and oxidized ascorbate in leaf cells of Arabidopsis thaliana and Nicotiana tabacum by high-resolution immuno electron microscopy. The accuracy and specificity of the applied method is supported by several observations. First, preadsorption of the ascorbate antisera with ascorbic acid or dehydroascorbic acid resulted in the reduction of the labeling to background levels. Second, the overall labeling density was reduced between 50 and 61% in the ascorbate-deficient Arabidopsis mutants vtc1-2 and vtc2-1, which correlated well with biochemical measurements. The highest ascorbate-specific labeling was detected in nuclei and the cytosol whereas the lowest levels were found in vacuoles. Intermediate labeling was observed in chloroplasts, mitochondria and peroxisomes. This method was used to determine the subcellular ascorbate distribution in leaf cells of plants exposed to high light intensity, a stress factor that is well known to cause an increase in cellular ascorbate concentration. High light intensities resulted in a strong increase in overall labeling density. Interestingly, the strongest compartment-specific increase was found in vacuoles (fourfold) and in plastids (twofold). Ascorbate-specific labeling was restricted to the matrix of mitochondria and to the stroma of chloroplasts in control plants but was also detected in the lumen of thylakoids after high light exposure. In summary, this study reveals an improved insight into the subcellular distribution of ascorbate in plants and the method can now be applied to determine compartment-specific changes in ascorbate in response to various stress situations

Erosion and soil and water conservation in South‐Kivu

Despite being one of the hotspots for soil erosion in the world, little is known regarding farmer's knowledge of soil erosion in the highlands of South-Kivu in the Democratic Republic of Congo. A proper understanding of farmers' knowledge regarding soil erosion and conservation measures is a prerequisite for implementing resilient erosion control measures. The objective of this study was therefore to assess farmers' knowledge of soil erosion, to document existing soil and water conservation (SWC) measures and to identify their adoption constraints in the highlands of South- Kivu. Data were collected using interviews with a semi-structured questionnaire involving 720 respondents from eight watersheds in four territories. Farmers reported eight main erosion indicators. As opposed to gullies (80% of farmers), rills were perceived as important erosion indicators by only 50% of farmers, despite their common occurrence. Farmers were largely unaware of the potential impact of their crops and cropping practices on erosion. Farmers knew about only a limited range of SWC measures, which were perceived to be little to moderately efficient. Furthermore, the average level of adoption was very low (21%). Adoption constraints varied widely depending on the SWC measure. Thus, future interventions need to place much greater emphasis on awareness regarding soil erosion and SWC measures, to strengthen farmers' capacity for experimentation and adaptation to new technologies and finally to create a policy and institutional environment that stimulates widespread adoption of SWC techniques