Characteristics of the tomato chromoplast revealed by proteomic analysis

Chromoplasts are non-photosynthetic specialized plastids that are important in ripening tomato fruit (Solanum lycopersicum) since, among other functions, they are the site of accumulation of coloured compounds. Analysis of the proteome of red fruit chromoplasts revealed the presence of 988 proteins corresponding to 802 Arabidopsis unigenes, among which 209 had not been listed so far in plastidial databanks. These data revealed several features of the chromoplast. Proteins of lipid metabolism and trafficking were well represented, including all the proteins of the lipoxygenase pathway required for the synthesis of lipid-derived aroma volatiles. Proteins involved in starch synthesis co-existed with several starch-degrading proteins and starch excess proteins. Chromoplasts lacked proteins of the chlorophyll biosynthesis branch and contained proteins involved in chlorophyll degradation. None of the proteins involved in the thylakoid transport machinery were discovered. Surprisingly, chromoplasts contain the entire set of Calvin cycle proteins including Rubisco, as well as the oxidative pentose phosphate pathway (OxPPP). The present proteomic analysis, combined with available physiological data, provides new insights into the metabolic characteristics of the tomato chromoplast and enriches our knowledge of non-photosynthetic plastids

Comparison of Carotenoid Content, Gene Expression and Enzyme Levels in Tomato (Lycopersicon esculentum) Leaves

Physiological conditions which lead to changes in total carotenoid content in tomatoplantlets were identified. Carotenoid levels were found to increase after the onset of a darkperiod during a normal 24h cycle. This rapid initial increase is followed by a steady decreasein carotenoid content throughout the night. A decrease in the expression of several caroteno-genic genes, namelypds,zds(carotenoid desaturases) andptox(plastid terminal oxidase),was observed following the removal of the light (when carotenoid content is at its highest).An increase in gene expression was observed before the return to light forpdsandzds(whencarotenoid levels were at their lowest), or following the return to light forptox.The phytoenedesaturation inhibitor norflurazon leads to a decrease coloured carotenoid content and, inthe light, this correlated withpdsandzdsgene induction. In the dark, norflurazon treatmentled to only a weak decrease in carotenoid content and only a small increase inpdsandzdsgene expression. The striking absence of phytoene accumulation under norflurazon treatmentin the dark suggests a down-regulation of carotenoid formation in darkness. However, pro-longed dark conditions, or treatment with photosynthetic inhibitors, surprisingly led to highercarotenoid levels, which correlated with decreased expression of most examined genes. Inaddition to light, which acts in a complex way on carotenoid accumulation and gene expres-sion, our results are best explained by a regulatory effect of carotenoid levels on the expres-sion of several biosynthetic genes. In addition, monitoring of protein amounts for phytoenedesaturase and plastid terminal oxidase (which sometimes do not correlate with gene expres-sion) indicate an even more complex regulatory pattern

Evidence for alternative electron sinks to photosynthetic carbon assimilation in the high mountain plant species Ranunculus glacialis

International audienceThe high mountain plant species Ranunculus glacialis has a low antioxidative scavenging capacity and a low activity of thermal dissipation of excess light energy despite its growth under conditions of frequent light and cold stress. In order to examine whether this species is protected from over-reduction by matching photosystem II (PSII) electron transport (ETR) and carbon assimilation, both were analysed simultaneously at various temperatures and light intensities using infrared gas absorption coupled with chlorophyll fluorescence. ETR exceeded electron consumption by carbon assimilation at higher light intensities and at all temperatures tested, necessitating alternative electron sinks. As photorespiration might consume the majority of excess electrons, photorespiration was inhibited by either high internal leaf CO2 molar ratio (C-i), low oxygen partial pressure (0.5% oxygen), or both. At 0.5% oxygen ETR was significantly lower than at 21% oxygen. At 21% oxygen, however, ETR still exceeded carbon assimilation at high C-i, suggesting that excess electrons are transferred to another oxygen consuming reaction when photorespiration is blocked. Nevertheless, photorespiration does contribute to electron consumption. While the activity of the water -water cycle to electron consumption is not known in leaves of R. glacialis, indirect evidence such as the high sensitivity to oxidative stress and the low initial NADP-malate dehydrogenase (NADP-MDH) activity suggests only a minor contribution as an alternative electron sink. Alternatively, the plastid terminal oxidase (PTOX) may transfer excess electrons to oxygen. This enzyme is highly abundant in R. glacialis leaves and exceeds the PTOX content of every other plant species so far examined, including those of transgenic tomato leaves overexpressing the PTOX protein. Finally, PTOX contents strongly declined during deacclimation of R. glacialis plants, suggesting their important role in photoprotection. Ranunculus glacialis is the first reported plant species with such a high PTOX protein content

Reduced P53 levels ameliorate neuromuscular junction loss without affecting motor neuron pathology in a mouse model of spinal muscular atrophy

Spinal Muscular Atrophy (SMA) is a childhood motor neuron disease caused by mutations or deletions within the SMN1 gene. At endstages of disease there is profound loss of motor neurons, loss of axons within ventral roots and defects at the neuromuscular junctions (NMJ), as evidenced by pathological features such as pre-synaptic loss and swelling and post-synaptic shrinkage. Although these motor unit defects have been widely described, the time course and interdependancy of these aspects of motor unit degeneration are unclear. Recent reports have also revealed an early upregulation of transcripts associated with the P53 signalling pathway. The relationship between the upregulation of these transcripts and pathology within the motor unit is also unclear. In this study, we exploit the prolonged disease timecourse and defined pre-symptomatic period in the Smn mouse model to perform a temporal analysis of the different elements of motor unit pathology. We demonstrate that NMJ loss occurs prior to cell body loss, and coincides with the onset of symptoms. The onset of NMJ pathology also coincides with an increase in P53-related transcripts at the cell body. Finally, using a tamoxifen inducible P53 knockout, we demonstrate that post-natal reduction in P53 levels can reduce NMJ loss, but does not affect other aspects of NMJ pathology, motor neuron loss or the phenotype of the Smn mouse model. Together this work provides a detailed temporal description of pathology within motor units of an SMA mouse model, and demonstrates that NMJ loss is a P53-dependant process. This work supports the role for P53 as an effector of synaptic and axonal degeneration in a die-back neuropathy

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Is It Possible to Overcome the GMO Controversy? Some Elements for a Philosophical Perspective

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