Changes in antioxidant systems in sunflower partial resistant and susceptible lines as affected by Sclerotinia sclerotiorum

Oligosaccharides: Defense Inducers, Their Recognition in Plants, Commercial Uses and Perspectives

Plants have innate immune systems or defense mechanisms that respond to the attack of pathogenic microorganisms. Unlike mammals, they lack mobile defense cells, so defense processes depend on autonomous cellular events with a broad repertoire of recognition to detect pathogens, which compensates for the lack of an adaptive immune system. These defense mechanisms remain inactive or latent until they are activated after exposure or contact with inducing agents, or after the application of the inductor; they remain inactive only until they are affected by a pathogen or challenged by an elicitor from the same. Resistance induction represents a focus of interest, as it promotes the activation of plant defense mechanisms, reducing the use of chemical synthesis pesticides, an alternative that has even led to the generation of new commercial products with high efficiency, stability and lower environmental impact, which increase productivity by reducing not only losses but also increasing plant growth. Considering the above, the objective of this review is to address the issue of resistance induction with a focus on the potential of the use of oligosaccharides in agriculture, how they are recognized by plants, how they can be used for commercial products and perspectives.

Genotype-Specific Antioxidant Responses and Assessment of Resistance Against Sclerotinia sclerotiorum Causing Sclerotinia Rot in Indian Mustard

Productivity of Indian mustard, an important oilseed crop of India, is affected by several pathogens. Among them, the hemibiotroph Sclerotinia sclerotiorum, which causes sclerotinia rot disease, is the most devastating fungal pathogen causing up to 90% yield losses. The availability of host resistance is the only efficient approach to control and understand the host-pathogen interaction. Therefore, the present investigation was carried out using six Indian mustard genotypes with contrasting behavior towards sclerotinia rot to study the antioxidant resistance mechanism against S. sclerotiorum. The plants at post-flowering stage were inoculated with five-day-old pure culture of S. sclerotiorum using artificial stem inoculation method. Disease evaluation revealed significant genotypic differences for mean lesion length among the tested genotypes, where genotype DRMR 2035 was found highly resistant, while genotypes RH 1569 and RH 1633 were found highly susceptible. The resistant genotypes had more phenolics and higher activities of peroxidase, catalase and polyphenol oxidase which provide them more efficient and strong antioxidant systems as compared with susceptible genotypes. Studies of antioxidative mechanisms validate the results of disease responses.

Response of photosynthetic capacity and antioxidative system of chloroplast in two wucai (Brassica campestris L.) genotypes against chilling stress

Chilling stress during the growing season could cause a series of changes in wucai (Brassica campestris L.). WS-1 (chilling-tolerant genotype) and Ta2 (chilling-sensitive genotype) were sampled in present study to explore the chilling tolerance mechanisms. Our results indicated that photosynthetic parameters exhibited lower level in Ta2 than in WS-1 under chilling stress. The rapid chlorophyll fluorescence dynamics curve showed that chilling resulted in a greater inactivation of photosystem II reaction center in Ta2. Reactive oxygen species and malondialdehyde content of chloroplast in Ta2 were higher than WS-1. The ascorbate-glutathione cycle in chloroplast of WS-1 played a more crucial role than Ta2, which was confirmed by higher activities of antioxidant enzymes including Ascorbate peroxidase, Glutathione reductase, Monodehydroascorbate reductase and Dehydroascorbate reductase and higher content of AsA and GSH. In addition, the ultrastructure of chloroplasts in Ta2 was more severely damaged. After low temperature stress, the shape of starch granules in Ta2 changed from elliptical to round and the volume became larger than that of WS-1. The thylakoid structure of Ta2 also became dispersed from the original tight arrangement. Combined with our previous study under heat stress, WS-1 can tolerant both chilling stress and heat stress, which was partly due to a stable photosynthetic system and the higher active antioxidant system in plants, in comparison to Ta2.

Transcriptomic and proteomic response of Manihot esculenta to Tetranychus urticae infestation at different densities

Tetranychus urticae (Acari: Tetranychidae) is an extremely serious cassava (Manihot esculenta) pest. Building a genomic resource to investigate the molecular mechanisms of cassava responses to T. urticae is vital for characterizing cassava resistance to mites. Based on the tolerance of cassava varieties to mite infestation (focusing on mite development rate, fecundity and physiology), cassava variety SC8 was selected to analyze transcriptomic and proteomic changes after 5 days of T. urticae feeding. Transcriptomic analysis revealed 698 and 2140 genes with significant expression changes under low and high mite infestation, respectively. More defense-related genes were found in the enrichment pathways at high mite density than at low density. In addition, iTRAQ-labeled proteomic analysis revealed 191 proteins with significant expression changes under low mite infestation. Differentially expressed genes and proteins were mainly found in the following defense-related pathways: flavonoid biosynthesis, phenylpropanoid biosynthesis, and glutathione metabolism under low-density mite feeding and plant hormone signal transduction and plant-pathogen interaction pathways under high-density mite feeding. The plant hormone signal transduction network, involving ethylene, jasmonic acid, and salicylic acid transduction pathways, was explored in relation to the M. esculenta response to T. urticae. Correlation analysis of the transcriptome and proteome generated a Pearson correlation coefficients of R = 0.2953 (P < 0.01), which might have been due to post-transcriptional or post-translational regulation resulting in many genes being inconsistently expressed at both the transcript and protein levels. In summary, the M. esculenta transcriptome and proteome changed in response to T. urticae, providing insight into the general activation of plant defense pathways in response to mite infestation.

Enzymatic activities and pathogenesis-related genes expression in sunflower inbred lines affected by Sclerotinia sclerotiorum culture filtrate

AIMS

Studying biochemical responses and pathogenesis-related gene expression in sunflower-Sclerotinia interaction can shed light on factors participating to disease resistance.

METHODS AND RESULTS

Partially resistant and susceptible lines were exposed to pathogen culture filtrate. The activity of antioxidant enzymes and proline was much more pronounced in partially resistant line. The more resistant to Sclerotinia sclerotiorum, the less (1,4)-β-glucanase activity was observed. PDF 1.2 and PR5-1 exhibited higher transcript abundance in the partially resistant line than in the susceptible line.

CONCLUSIONS

Considering the dual roles of oxalic acid, activation of the antioxidant system in partially resistant line might lead to suppression of oxidative burst which is beneficial for the growth of fungus at later stages of infection. The ability of the partially resistant line in balancing antioxidant enzymes could reserve H₂ O₂ as a substrate for peroxidase that might lead to lignification. The contribution of (1,4)-β-glucanase defence responses against Sclerotinia was observed. The roles of SA and JA marker genes were demonstrated in sunflower defence responses.

SIGNIFICANCE AND IMPACT OF THE STUDY

The time of antioxidant system activation in host is important in order to contribute to defence responses. To date, the changes in the expression of PR1 and PDF 1.2 and contribution of (1,4)-β-glucanase enzyme in sunflower defence responses were not reported in previous studies.