Impact of pulsed UV‐B stress exposure on plant performance: How recovery periods stimulate secondary metabolism while reducing adaptive growth attenuation

Abstract

Upon continuous stress exposure, plants display attenuated metabolic stress responses due to regulatory feedback loops. Here, we have tested the hypothesis that pulsed stress exposure with intervening recovery periods should affect these feedback loops, thereby causing increased accumulation of stress-induced metabolites. The response of Arabidopsis plantlets to continuous UV-B exposure (C ) was compared with that of pulsed UV-B exposure (P ). The differential responses to P versus C were monitored at the level of gene expression and metabolite accumulation, using wild type (WT) and different mutant lines. In comparison with C , P increased sinapyl and flavonol (S + F) content, whereas adaptive growth attenuation was reduced. Furthermore, in a myb4 mutant (AtMYB4, repressor-type R2R3-MYB transcription factor), the S + F content was increased only for C , but not beyond the level for P observed in WT. These observations and the ability of AtMYB4 to repress AtMYB12/AtMYB111-mediated activation of target gene promoters (pCHS and pFLS) indicate that the increase of S + F content after P observed in WT plants results from reduced feedback inhibition by AtMYB4. The results support the notion that stress-induced metabolic changes not necessarily cause a growth penalty. Furthermore, the observed P -induced increase in flavonol accumulation may stimulate reevaluation of commercial plant production practices.

Physiologic and Metabolic Changes in Crepidiastrum denticulatum According to Different Energy Levels of UV-B Radiation

“…First, UVR8 dimer is converted to monomers by low-energy UV-B light, and the monomer then combines with CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1) to form a complex that stimulates ELONGATED HYPOCOTYL5 (HY5) transcription factor to activate stress defense responses. This leads to promote the biosynthesis of UV-B absorbing compounds, such as flavonoids, anthocyanins, and HCAs, which act as a sunscreen [ 9 , 10 , 35 , 36 , 37 , 38 ]. In addition, HY5 regulates a number of genes involving in the terpene biosynthesis pathway [ 39 ], and [ 40 , 41 ] reported that the relatively low UV-B radiation with 4.75 kJ d −1 induced the sesquiterpenes biosynthesis related to cell membrane stability, protecting leaves from UV-B-induced rapid heating.…”

“…These compounds synthesized via UVR8 pathway are involved in protective responses against environment-induced oxidative stress because of their high antioxidant capacity [ 35 , 36 , 37 , 38 , 42 ]. Secondly, ROS produced in chloroplasts, mitochondrias, and apoplasts due to high level of UV-B light generate ROS waves, which mediate rapid systemic signaling, activating ROS-scavenging pathway to stimulate the biosynthesis of antioxidant secondary metabolites [ 8 , 9 , 10 ]. If stress persists or stress level is high, the accumulation of ROS generated from these pathways will be greater than that of antioxidants level, which subsequently damages plants [ 7 , 8 , 9 ].…”

“…), by mediating rapid systemic signaling involved in plant defense [ 8 ]. In addition, UV Resistance Locus8 (UVR8) initiates the stress signaling response by receiving UV-B light [ 2 , 7 , 9 , 10 ]. Among UV-B stress responses, an important change in terms of secondary metabolites is the accumulation of phenolic compounds, such as flavonoids, anthocyanins, and hydroxycinnamic acids (HCAs), that function as sunscreens in vacuoles of epidermal cells to protect important subcellular components from UV-B light [ 11 , 12 , 13 ].…”

Stress priming, memory, and signalling in plants

“…Recovery periods between the stress events may support “training.” A study by Höll et al () compared the effects of pulsed UV‐B exposure on levels of plant metabolites involved in UV‐B protection with those of continuous UV‐B exposure. Although the total duration of pulsed and continuous UV‐B exposure was the same, plants experiencing the pulsed exposure accumulated more UV‐B‐protective flavonols.…”

Sunburn in Grapes: A Review

“…When allowed recovery periods, the capacity of plants to adapt to different stresses is enhanced when compared to continuous periods of stress ( Figure 6). In an experiment comparing constant doses of UV-B (6 h at 0.04 mW cm −2 ) and pulsed doses (6 × 1 h intervals interspersed with 30 min recovery periods), Arabidopsis plants allowed recovery periods produced more photoprotectants; 27% more total flavonols and sinapyl derivates, 38% more kaempferols, and 90% more quercetins (Höll et al, 2019). The authors also demonstrated that the amount by which these compounds increase depends on the duration of the recovery periods, with shorter recovery periods showing almost no differences when compared to plants treated continuously.…”