Physiological responses of maca (Lepidium meyenii Walp.) plants to UV radiation in its high-altitude mountain ecosystem

Abstract

Ultraviolet (UV) radiation is a small fraction of the solar spectrum, which acts as a key environmental modulator of plant function affecting metabolic regulation and growth. Plant species endemic to the Andes are well adapted to the harsh features of high-altitude climate, including high UV radiation. Maca (Lepidium meyenii Walpers) is a member of Brassicaceae family native to the central Andes of peru, which grows between 3500 and 4500 m of altitude, where only highland grasses and few hardy bushes can survive. even though maca has been the focus of recent researches, mainly due to its nutraceutical properties, knowledge regarding its adaptation mechanisms to these particular natural environmental conditions is scarce. in this study, we manipulated solar UV radiation by using UV-transmitting (control) or blocking (UV-block) filters under field conditions (4138 m above the sea level) in order to understand the impact of UV on morphological and physiological parameters of maca crops over a complete growing season. Compared to the UV-blocking filter, under control condition a significant increase of hypocotyl weight was observed during the vegetative phase together with a marked leaf turnover. Although parameters conferring photosynthetic performance were not altered by UV, carbohydrate allocation between above and underground organs was affected. Control condition did not influence the content of secondary metabolites such as glucosinolates and phenolic compounds in hypocotyls, while some differences were observed in the rosettes. These differences were mainly related to leaf turnover and the protection of new young leaves in control plants. Altogether, the data suggest that maca plants respond to strong UV radiation at high altitudes by a coordinated remobilization and relocation of metabolites between source and sink organs via a possible UV signaling pathway.The Andes form the longest and one of the highest mountain ranges in the world, with a width of approximately 400 Km and over 100 peaks above 6000 m of altitude along the west coast of South America 1 . An extensive biodiversity of plant species is endemic to this region and these have been used for centuries by the native population. Interestingly, these crops are well adapted to the harsh climate of the Andes including drought, freezing temperatures, strong wind and high ultraviolet (UV) radiation 2 . UV represents a small fraction of the solar spectrum and based on its biological effects it is divided into UVC (100-280 nm), UVB (280-315 nm) and UVA (315-400 nm). However, only UVA and fraction of UVB radiation reach the Earth surface, of which UVB has the highest energy in the solar spectrum and thus has a major impact on all organisms. Moreover, levels of UVB, as well as those of UVA, vary in time and space depending on the weather, climate and geographical conditions, such as season of the year, altitude, latitude and atmospheric surface 3 .In the past decades, there has been an increased interest in the effects of UVB radiation on plant physiology and...

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