The present study examined the effects of Candidatus Phytoplasma solani infection on antioxidative metabolism in leaves and roots of carrot (Daucus carota L.). Disease symptoms appeared at the end of June in the form of the chlorosis on some of the leaves, which became intensely red one week later, while the previously healthy leaves from the same branch becme chlorotic. A few days later, all leaves from the infected leaf branch were intensely red. Infected plants also had slower growth compared to the healthy ones with fewer leaf branches developed. The roots of infected plants were less developed, seared, or gummy with or without brown-colored root hair. The presence of the pathogen was detected by sequencing the 16S rRNA. National Center for Biotechnology Information (NCBI) BLAST analyses of the obtained sequence revealed 100% identity of tested strain with deposited Ca. Phytoplasma solani strains from various countries and hosts, all belonging to the “stolbur” group (16SrXII-A). Identity of 99.74% was found when the tested Serbian strain (MF503627) was compared with the reference stolbur strain STOL11 (AF248959). The oxidative damage of membranes in carrot cells was accompanied by a decrease in the content of photosynthetic pigments. Furthermore, for the determination of specific scavenging properties of the extracts, in vitro antioxidant assay was performed. In phytoplasma-infected carrot leaves, there was a greater reduction in the level of glutathione content (GSH); however; flavonoids and anthocyanidins seem to be responsible for the accompanied increased antioxidative capacity against hydroxyl radical and hydrogen peroxide.

Chloroplast movement rapidly ameliorates the effects of suboptimal light intensity by accumulating along the periclinal cell walls, as well as the effects of excess light by shifting to the anticlinal cell walls. These acclimation responses are triggered by phototropins located at the plasma membrane and chloroplast envelope. Here, we used a recently developed non-invasive system sensitive to very small changes in red light leaf transmittance to perform long-term continuous measurements of dark–light transitions. As a model system, we used variegated Pelargonium zonale leaves containing green sectors (GS) with fully developed chloroplasts and achlorophyllous, white sectors (WS) with undifferentiated plastids, and higher phototropin expression levels. We observed biphasic changes in the red-light transmittance and oscillations triggered by medium intensities of white light, described by a transient peak preceded by a constant decrease in transmittance level. A slight change in red-light transmittance was recorded even in WS. Furthermore, the chloroplast position at lower light intensities affected the rapid light curves, while high light intensity decreased saturated electron transport, maximum quantum efficiency of photosystem II, and increased non-photochemical quenching of chlorophyll fluorescence and epidermal flavonoids. Our results extend the knowledge of light-dependent chloroplast movements and thus contribute to a better understanding of their role in regulating photosynthesis under fluctuating light conditions.

Xanthomonas campestris pv. campestris (Xcc), the causal agent of black rot, has a significant impact on cabbage production worldwide. The goal of this research was to evaluate the effect of preventive foliar treatments with Bacillus velezensis strain RD-FC 88 on the primary and secondary metabolism of Xcc-infected cabbage cv. Futoški plants. Special attention was given to measuring metabolites’ changes, aiming to determine the influence of the applied biocontrol treatment on the development of plant immune response and resistance to pathogen. This study reports the first comprehensive biochemical and physiological analysis of the interaction between host plant, biocontrol strain and pathogen, thus providing novel insight into black rot management. Pathogen inoculation caused a significant decrease in the majority of measured metabolites, including most free amino acids (Gln, Ala, BCAA), phenolics, and glucosinolates. Preventive application of B. velezensis strain in Xcc-infected plants restored the levels of aromatic amino acids, Asp, Glu, Leu, Val, and Ala to control values. A similar pattern was observed in aliphatic glucosinolates sinigrin and glucoiberin, as well as for the indolic glucosinolate 4-methoxy-glucobrassicin. Additionally, increased accumulation of hydroxybenzoic acids, hydroxycinnamic acids, and kaempferol derivatives was also observed in the plants treated with the biocontrol strain and subsequently infected with Xcc, compared to plants solely infected with Xcc. The obtained results imply that the RD-FC 88 strain holds potential as an efficient priming agent, capable of stimulating cabbage cv. Futoški defense responses and enhancing its resistance to Xcc.