Abstract
BackgroundShade avoidance syndrome (SAS) commonly occurs in plants experiencing vegetative shade, causing morphological and physiological changes that are detrimental to plant health and consequently crop yield. As the effects of SAS on plants are irreversible, early detection of SAS in plants is critical for sustainable agriculture. However, conventional methods to assess SAS are restricted to observing for morphological changes and checking the expression of shade-induced genes after homogenization of plant tissues, which makes it difficult to detect SAS early.ResultsUsing the model plant Arabidopsis thaliana, we introduced the use of Raman spectroscopy to measure shade-induced changes of metabolites in vivo. Raman spectroscopy detected a decrease in carotenoid contents in leaf blades and petioles of plants with SAS, which were induced by low Red:Far-red light ratio or high density conditions. Moreover, by measuring the carotenoid Raman peaks, we were able to show that the reduction in carotenoid content under shade was mediated by phytochrome signaling. Carotenoid Raman peaks showed more remarkable response to SAS in petioles than leaf blades of plants, which greatly corresponded to their morphological response under shade or high plant density. Most importantly, carotenoid content decreased shortly after shade induction but before the occurrence of visible morphological changes. We demonstrated this finding to be similar in other plant species. Comprehensive testing of Brassica vegetables showed that carotenoid content decreased during SAS, in both shade and high density conditions. Likewise, carotenoid content responded quickly to shade, in a manner similar to Arabidopsis plants.ConclusionsIn various plant species tested in this study, quantification of carotenoid Raman peaks correlate to the severity of SAS. Moreover, short-term exposure to shade can induce the carotenoid Raman peaks to decrease. These findings highlight the carotenoid Raman peaks as a biomarker for early diagnosis of SAS in plants.
Highlights
Shade avoidance syndrome (SAS) commonly occurs in plants experiencing vegetative shade, causing morphological and physiological changes that are detrimental to plant health and crop yield
Raman spectra analysis of Arabidopsis leaf blades and petioles during SAS To investigate if Raman spectroscopy could identify metabolites that change in response to shade, we established shade conditions that were low in Red:Far-red (R:FR) light to induce SAS in Arabidopsis plants
These morphological changes were accompanied by the shade-induced expression of marker genes such as A. thaliana Homeobox Protein 2/4 (AtHB2/AtHB4) and Phytochrome Interacting Factor 3-Like 1 (PIL1), which were highly induced under short durations of moderate shade (MS) and deep shade (DS) treatment (Fig. 1c) [7, 22]
Summary
Shade avoidance syndrome (SAS) commonly occurs in plants experiencing vegetative shade, causing morphological and physiological changes that are detrimental to plant health and crop yield. Conventional methods to assess SAS are restricted to observing for morphological changes and checking the expres‐ sion of shade-induced genes after homogenization of plant tissues, which makes it difficult to detect SAS early. Upon exposure to vegetative shade, plants respond by reaching for more light to overcome the shaded condition. This adaptive response, known as shade avoidance syndrome (SAS), includes stem and petiole elongation, hyponastic leaves, reduced leaf development, early flowering, and increased senescence [1, 2]. SAS affects many agronomic traits such as reduced grain yield or plant biomass [3, 4]
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