For example, the higher rate of photosynthesis with higher irradiance reaches saturation, after which the excess light can cause photo-oxidative damage ( Li et al. If provided in excess, however, it can be harmful. Light is of utmost importance to plants as it provides energy and clues about the environment. Molecular mechanisms linking carbohydrate accumulation with down-regulation of carbon-fixing enzymes are discussed. We postulate that the continuous light-induced injury in tomato is caused by down-regulation of photosynthesis, showing characteristics of both cytokinin-regulated senescence and light-modulated retrograde signaling. A strong negative correlation between sucrose and starch content with the severity of continuous light-induced damage quantified as the maximum quantum efficiency of PSII ( F v/ F m) was found across several abnormal light/dark cycles, supporting the hypothesis that carbohydrates play an important role in the continuous light-induced injury. Analysis of metabolomics and transcriptomics data reveals a clear effect of continuous light on sugar metabolism and photosynthesis. Here, we use non-targeted metabolomics and transcriptomics analysis as well as hypothesis-driven experiments with continuous light-tolerant and -sensitive tomato lines to explore the long-standing proposed role of carbohydrate accumulation in this disorder. Understanding the mechanism of these injuries is valuable, as important pathways regulating photosynthesis, such as circadian, retrograde and light signaling pathways are probably involved. Tomato ( Solanum lycopersicum), for example, develops mottled chlorosis and necrosis when exposed to continuous light. If provided in unnatural long photoperiods, however, it can be harmful and even lethal. This review describes the background to PLRV and points towards these new developments.Light is most important to plants as it fuels photosynthesis and provides clues about the environment. These are, its phloem confinement, its movement in infected plants, its ability to suppress gene silencing and new ideas about the structure of its particles. Key attractions: In recent years some interesting features of PLRV have emerged that are the focus of further investigation. A decade or so of molecular study has revealed the many features of PLRV that are characteristic of its family. Its isometric particles are persistently transmitted by aphids in a non-propagative manner, it multiplies largely in phloem tissue and disease symptoms reflect this localization. Biological properties: The biology of PLRV is that of a classic luteovirus. Infection, especially from infected seed potato stocks, causes leafrolling and stunting, the extent depending on the potato cultivar. PLRV is a common pathogen of potato, and closely related isolates are occasionally found in tomato, but no other crops are affected. PLRV has a limited host range about 20 largely solanaceous species have been infected experimentally. The genome is a single 5.8 kb positive sense RNA that has neither a 5'-cap nor 3' poly(A) but carries a VPg. Physical properties: PLRV particles are isometric and c. Isolates are known from most continents, presumably all spread in potato material derived from the Andean region of South America. SUMMARY Taxonomy: PLRV is the type species of the genus Polerovirus, in the family Luteoviridae.
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