Rapid metabolite response in leaf blade and petiole as a marker for shade avoidance syndrome

Abstract

Background Shade 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. Results Using 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. Conclusions In 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.

Carotenoid Biosynthesis and Plastid Development in Plants: The Role of Light

“…On the other hand, when plants are grown in the shade (low R/FR ratio), for instance, when they grow under a dense canopy, they perceive higher levels of FR due to the selective light reflection on the foliage. This causes a decrease in the carotenoid synthesis compared to W light [ 93 , 94 ] and PSY expression, including different FR intensities such as moderate shade (R/FR: 0.7) or severe shade (R/FR: 0.2) [ 94 ]. At the molecular level, active PHYA physically interacts with PIFs and COP1 in the nucleus, fulfilling the same function that PHYB carries out in W light ( Figure 2 ) [ 86 , 95 ].…”

Rapid Detection and Quantification of Plant Innate Immunity Response Using Raman Spectroscopy

“…Several groups have used Raman spectroscopy to analyze a number of crop plants infected with bacterial, fungal, and viral pathogens, and, in most cases, a decrease in carotenoid was consistently seen; however, a decrease in carotenoid has also been observed with abiotic stresses. We too have previously detected a decrease in carotenoid contents in the leaf blades and petioles of Arabidopsis with shade avoidance syndrome (SAS) using Raman spectroscopy (Altangerel et al, 2017 ; Sng et al, 2020 ). By contrast, we found that a transient increase in carotenoids is an early event in PTI.…”

Integration of Light and Auxin Signaling in Shade Plants: From Mechanisms to Opportunities in Urban Agriculture

“…Weak light increases the Chl b content, decreases the Chl a :Chl b ratio, increases the light-harvesting pigment complex content, and increases the photosystem-II(PSII)-to-photosystem-I (PSI) ratio [ 11 ]. In addition to morphological changes, sun–shade transformation also leads to a large number of metabolite adjustments [ 12 ]. Defense-related metabolites, such as phenolic compounds and alkaloids, are usually downregulated under shade, whereas volatile terpenes display uncertain changes [ 13 ].…”