Effects Of Supplementary Uv-B Radiation On Pea (Pisum Sativum L. Cv. Massey Gem) Leaves Photosynthesis

ABSTRACT Maryani and J.T. Wiskich. 1999. Effects of supplementary UV-B radiation on pea (Pisum sativum L. cv. Massey Gem) leaves photosynthesis. Biologi2(8): 397-410. I Pea plants subjected to UV-B radiation decreased their chlorophyll content. The i rates of photosynthesis measured in intact leaves and leaf slices also changed underUV-B treatment. The intact leaves taken from high UV-B plants showed a rapid decreasein the net photosynthesis to about 69%, while in natural and low UV-B treatment was j about 35%. These results may be related to their decrease of stomatal conductivity and chlorophyll content. The rates of photosynthesis in leaf slices also decreased under UV-B treatment. When expressed on both leaf weight and chlorophyll basis, the activity of CO2-dependent O2 evolution. Rates of O2 evolution in chloroplasts from UV-B treated leaves were lower than controls. As UV-B has damaged the structure of chloroplasts, the reduction of photosynthesis rates could be associated to the damage thylakoid and envelope membrane. It was found that UV-B treatment also inhibited electron transport rates when artificial acceptors were applied with grana solution (broken chloroplasts). Key words: UV-B radiation, peas, photosynthesi

Clean innovation and heterogeneous financing costs

Access to finance is a major barrier to clean innovation. We incorporate heterogeneous and endogenous financing costs in a directed technical change model and identify optimal climate mitigation policies. The presence of a financing experienceeffect pushes the policy- maker to strengthen policies in the short-term, both to shift innovation and production towards clean sectors and to reduce the financing cost differential across technologies, which further facilitates the transition. The optimal climate policy mix between carbon taxes and clean research subsidies depends on the drivers of the experience effect. In our benchmark scenario, where clean financing costs decline as cumulative clean output increases, we find an optimal carbon price premium of 47% in 2025, relative to a case with no financing costs

Clean Innovation and Heterogeneous Financing Costs

Access to finance is a major barrier to clean innovation. We incorporate heterogeneous and endogenous financing costs in a directed technical change model and identify optimal climate mitigation policies. The presence of a financing experience effect induces more ambitious policies in the short-term, both to shift innovation and production towards clean sectors and to reduce the financing cost differential across technologies, which further facilitates the transition. The optimal climate policy mix between carbon taxes and clean research subsidies depends on whether experience is gained through clean production or research. In our benchmark scenario, where clean financing costs decline as cumulative clean output increases, we find an optimal carbon price premium of 47% in 2025, relative to a case with no financing costs

Essays on modelling the economics of energy and the climate

This thesis consists of four papers. Using different formulations of climate tipping points that trigger abrupt and irreversible damages, the first paper derives optimal environmental taxes in an analytically tractable model and depend on only a few parameters and a temperature projection. In a stylised approach, optimal taxes are constant as a ratio of income and are the sum of a deterministic damage component and a tipping risk component. If a tipping point may be triggered by temperature crossing a threshold, optimal tax-to-income ratios eventually fall and the price for short-lived methane emissions relative to long-lived carbon dioxide emissions should rise over time. The second paper considers a hypothetical choice between a carbon tax and a clean research subsidy. This paper argues that the absence of a non-energy sector has led some previous literature to find that subsidies outperform taxes. An integrated assessment model with endogenous technology is described. Numerical exercises find that a permanent global tax-only policy outperforms a permanent subsidy-only policy and this result is robust to many different parameter settings and assumptions. However, in the more optimistic case where optimal policy begins in 2050, the performances of subsidy-only and tax-only policies in the interim are closer. The third paper argues that a clean transition in electricity generation will likely be driven by variable renewable energy. The elasticity of substitution between wind and solar inputs and dirty inputs in electricity is estimated to be 3 or more by fitting an aggregate production function to OECD panel data. A high elasticity is consistent with detailed electricity models which also predict that the substitutability decreases as the share of clean inputs rises, as integrating intermittent energy supply becomes increasingly difficult. A simple dispatch model of electricity generation demonstrates this characteristic. Decreasing substitutability implies higher costs of a clean transition, greater costs from regions transitioning sequentially rather than together, and a greater role for carbon taxes over research subsidies. The fourth paper discusses how the framework used to endogenise technology growth by Acemoglu et al. (2012) can exhibit increasing returns to research and hence multiple equilibria, including an unstable interior equilibrium. The paper discusses several methods to determine how a unique equilibrium might be specified. Alternative methods can produce substantially different results when the elasticity of substitution between clean and dirty inputs is high

Regulation of alternative oxidase kinetics by pyruvate and intermolecular disulfide bond redox status in soybean seedling mitochondria

AbstractTwo factors known to regulate plant mitochondrial cyanide-resistant alternative oxidase activity, pyruvate and the redox status of the enzyme's intermolecular disulfide bond, were shown to differently affect activity in isolated soybean seedling mitochondria. Pyruvate stimulated alternative oxidase activity at low levels of reduced ubiquinone, shifting the threshold level of ubiquinone reduction for enzyme activity to a lower value. The disulfide bond redox status determined the maximum enzyme activity obtainable in the presence of pyruvate, with the highest rates occurring when the bond was reduced. With variations in cellular pyruvate levels and in the proportion of reduced alternative oxidase protein, a wide range of enzyme activity is possible in vivo

Anatomical changes of Pea(Pisum sativum L.cv Massey Gem) and wheat (Triticumaestivum L.var Machetti) leaves exposed to Uv-B radiation = Perubahan struktur anatomi daun kacang ercis ...

ABSTRACT: Pea leaves exposed to UV -B increased their leaf thickness at the mid-rib area, but lowered thickness at non vascular bundle areas. In wheat leaves, both leaf thickness at the mid-rib and non vascular bundle areas increased under UV-B radiation. UV-B radiation appeared to damage the adaxial epidermal and some mesophyll cells of pea leaves, but not in wheat. Electron microscopical studies showed that the general structure of cells from treated pea leaves was different to that control leaves. The collapse of epidermal cells was extreme in some areas, leading to disappearance of the protoplasm with the cell wall becoming pressed, leaving a small structure filled with granular material. Collapsed epidermis was accompanied by some internal damage to palisade layers, where most of cells were disorganized, being empty and columnar. Damaged palisade samples from low and high UV -B treated leaves contained altered chloroplasts and disorganized cells. The altered chloroplasts structure displayed a more open system of thylakoids and lamella membranes. Their photosynthetic lamellae tended to be swollen, with a reduction in thylakoid number, smaller grana, an increase in intergrana spaces, more osmiophilic globuli and poorly defined membranes. Mitochondria were sometimes smaller, with fewer cristae and showed poor membrane structure. In contrast, the general ultrastructure of cells from treated wheat leaves was similar to that of the control leaves. Key words: leaf anatomy, pea, wheat, UV-B radiation