The Diurnal Rhythm of Brassica napus L. Influences Contents of Sulfur-Containing Defense Compounds and Occurrence of Vascular Occlusions during an Infection with Verticillium longisporum

Abstract

Reduction in atmospheric sulfur and intensified agriculture have led to sulfur deficiency, often correlated with a higher susceptibility to pathogens. The spread of fungal pathogens, such as the soil-born Verticillium longisporum, was observed. Defense responses of infected plants are linked to sulfur-containing compounds including glucosinolates (GSLs). Some pathogens infect their hosts at specific time periods during the day. To investigate the relation of sulfur-containing metabolites with diurnal effects of infection time points, Brassica napus plants cultivated at two different sulfur supplies, were infected with V. longisporum at four different time points during the day. It was demonstrated that 3, 7 and 14 days after inoculation the infected plants differed in their infection rate depending on the time point of infection. Additionally, infected plants had higher contents of sulfur-containing metabolites, such as specific GSLs, in comparison to non-infected plants. Sufficient sulfur fertilization was always reflected in higher contents of sulfur-containing compounds as well as a lower rate of infection compared to sulfur-deprived plants. On the microscopic level vascular occlusions in the hypocotyl were visible and the amount was dependent on the time point of infection. The results might be used to optimize sulfur fertilization to reduce susceptibility to V. longisporum.

The Versatile Roles of Sulfur-Containing Biomolecules in Plant Defense—A Road to Disease Resistance

“…Remarkably, they showed that infection with V. longisporum also seems to enhance the synthesis of iGSLs in sulfur-deprived B. napus plants; despite the fact that these plants are very deficient in sulfur they managed to synthesize more iGSLs compared to their infected sulfur-sufficient counterparts. This phenomenon highlights the importance of iGSLs in plant defense [188].…”

“…Overexpression of BoTGG1 in A. thaliana leads to accelerated stomatal closure and inhibited stomatal reopening during the infection of Pst DC3000 [187]. Later it was described that the host response to Verticilium longisporum infection differs in Brassica napus plants grown in sulfur sufficient vs. deficient conditions [188]. These authors found that infected plants always showed higher contents of sulfur-containing metabolites, such as specific GSLs, in comparison to non-infected plants.…”

“…These authors found that infected plants always showed higher contents of sulfur-containing metabolites, such as specific GSLs, in comparison to non-infected plants. Sufficient sulfur fertilization is generally reflected in higher contents of sulfur-containing compounds, as well as a lower rate of infection compared to sulfur-deprived plants [188]. Remarkably, they showed that infection with V. longisporum also seems to enhance the synthesis of iGSLs in sulfur-deprived B. napus plants; despite the fact that these plants are very deficient in sulfur they managed to synthesize more iGSLs compared to their infected sulfur-sufficient counterparts.…”

Time of day of leaf wounding determines plant biomass and affects the interplay between growth and defence in Brassica crops

“…In this sense, recent advances provide unambiguous proof supporting rhythmic oscillation of a broad range of specialized compounds related with plant immunity, cell wall integrity and antioxidant capacity (Goodspeed et al 2012(Goodspeed et al , 2013Jander 2012;Atamian & Harmer 2016;Soengas et al 2018aSoengas et al , 2018bLiebelt et al 2019). Consistent with such oscillations, specialized metabolites that mediate plant defence are synchronized with Lepidoptera, aphid and pathogen circadian behaviour in Arabidopsis thaliana and related Brassica crops (Goodspeed et al 2012(Goodspeed et al , 2013Lei et al 2019;Rupp et al 2020). More recently, Doghri et al (2022) revealed that induction of glucosinolates (GSL), major plant defence metabolites in the Brassicaceae, depends on the time during the day at which the stress event (attack) takes place.…”

Importance of Daily Rhythms on Brassicaceae Phytochemicals

“…Given the effect of the phytohormones SA, JA, and ET on the contents of GSLs; individual and total phenolic compounds; and carotenoid, chlorophyll and, anthocyanin content by affecting their gene regulation of metabolic biosynthesis, it would be expected that phytochemical accumulation is also involved in the response of the plant clock under pathogen infection. Supporting this notion, a recent study seems to indicate the importance of diurnal rhythms in the accumulation of sulfur-containing defense compounds in B. napus, including GSLs, against the fungal pathogen Verticillium longisporum [72]. Therefore, time of the day and circadian rhythms seem to play a role in the functionality of the plant immune system, which may affect the virulence of pathogens and the overall outcome of host-pathogen relationship.…”