Balancing Damage via Non-Photochemical Quenching, Phenolic Compounds and Photorespiration in Ulva prolifera Induced by Low-Dose and Short-Term UV-B Radiation

Abstract

The Yellow Sea green tide (YSGT) is the world’s largest transregional macroalgal blooms, and the causative species Ulva prolifera (U. prolifera) suffers from ultraviolet-b radiation (UVBR) during the floating migration process. Previous study confirmed that U. prolifera displayed a wide variety of physiological responses characterized as acclimation to UVBR, while the response mechanisms against low-dose and short-term radiation (LDSTR) are not clear. A study with photosynthetically active radiation (PAR) and UVBR was designed: normal light (NL: 72 μmol photons m−2 s−1), NL+0.3 (UVBR: 0.3 W·m−2), and NL+1.6 (UVBR: 1.6 W·m−2). The results showed that high-dose UVBR inhibited photosynthesis in thalli, especially under long-term exposure, while a variety of physiological responses were observed under LDSTR. The inhibition of photosynthesis appeared to be ameliorated by the algae under LDSTR. Further analysis showed that U. prolifera achieved balancing damage by means of non-photochemical quenching (NPQ), accumulation of phenolic compounds coupled with the ASA-GSH cycle involved in the antioxidant process and enhanced photorespiratory metabolism under LDSTR. This study provides new insights into the balancing damage mechanisms of U. prolifera under LDSTR, enabling the thalli to adapt to the light conditions during the long duration and distance involved in floating migration.

Acclimation of intertidal macroalgae Ulva prolifera to UVB radiation: the important role of alternative oxidase

“…GO, as a key enzyme of photorespiration, plays an important role in maintaining the reduction equivalent of the thalli [35,56]. The important role of photorespiration in the adaptation of U. prolifera to stresses has been demonstrated in our previous studies [43]. In the present study, under HL conditions, AOX regulated the redox equivalent within the photosynthetic system by modulating the photorespiration process with GO as the key enzyme, so as to avoid an excessive reduction equivalent and optimize the photosynthetic activity of the thalli.…”

“…GO activity can be used to indicate the photorespiration flux [55,56]. Our previous research has confirmed that GO activity is positively correlated with other key enzymes, namely serine: glyoxylate aminotransferase (SGAT) and glycerate kinase (GLYK), in the photorespiration pathway when U. prolifera is exposed to short-term and low-intensity UVB radiation [43]. In addition, rice plants induced by antisense GO showed an obvious photorespiration defect phenotype [57], and in related research on Jatropha curcas plants under severe drought stress, GO activity was used to further verify the occurrence of photorespiration [58].…”

“…AOX was found to be sensitive to UVB stress and participated in the response process of thalli to UVB [33,41,42]. UVB, as a common type of abiotic stress, has been widely studied and found to have a significant inhibition on photosynthetic components in macroalgae [16,18,43]. It has also been confirmed that AOX plays an important role in maintaining the normal operation of photosynthesis when plants are under abiotic stresses [22,26,44].…”

Exploring the Physiological Multiplicity of Native Microalgae from the Ecuadorian Highland, Italian Lowland and Indoor Locations in Response to UV-B

“…Thus, it is possible that in F4, the applied acute UV-B resulted in a negative stress due to the lack of other co-occurring stresses, as demonstrated in a recent study where the UV-B acted as a ‘positive stress’ when it was presented with another abiotic variable [ 31 ]. Consistently, F4 exposed to continuous acute UV-B (1.7 W m −2 ) for 18 h resulted in a significant decline of the photosynthetic activity, indicating that this acute UV-B dose induced photoinhibition probably due to the imbalance of pro-oxidant production and scavenging capacity in F4 cells [ 32 , 33 , 34 , 35 ].…”

“…Indeed, TAC content was maintained at control levels during the experimental period, indicating that these non-enzymatic antioxidants were still functioning and were important during UV-B acclimation. Since enzymatic and non-enzymatic antioxidants may have a good complementary function in the protection of cells from UV-induced photo-oxidative damage [ 9 , 32 , 35 ], it would be interesting to identify those metabolites involved in LG1 photoacclimation.…”