Agnieszka Waśkiewicz

Phenolic Content Changes in Plants Under Salt Stress

Phenolics are one of the main group of plant secondary metabolites, including over 9,000 various compounds. They possess a wide range of biological functions in plants, such as protection from UV light, defense against pathogens, pigmentation to attract pollinators and protection from reactive oxygen species generated when aerobic or photosynthetic metabolism is impaired by various environmental stresses such as salt stress.

Nonenzymatic Antioxidants in Plants

Oxidative stress is caused by a wide range of abiotic and biotic factors including salinity, pathogen colonization, UV stress, herbicide activity and oxygen deficiency. These affect biochemical, physiological, developmental and structural processes within individual plants and plant communities. Under oxidative stress plants produce some defense mechanisms to protect themselves from the spectrum of harmful effects. Aside from the enzymatic antioxidants such as superoxide dismutase, peroxidase and catalase, the formation of reactive oxygen species (ROS) is also prevented by a nonenzymatic antioxidant system – the low molecular mass compounds such as glutathione, ascorbic acid, α-tocopherol, carotenoids and phenolic compounds. The mechanism of action of these molecules is based on modification of the cell metabolic functions, aimed at interacting with the polyunsaturated acyl groups of lipids to stabilize membranes, playing a protective role against the ROS that are formed from photosynthetic and respiratory processes and synergic function with other antioxidants.

Role of Glutathione in Abiotic Stress Tolerance

Glutathione (GSH) is a nonprotein, low molecular weight tripeptide (γ- glutamylcysteinylglycine) in most plant tissues. GSH is synthesized from glutamate (Glu), cysteine (Cys) and glycine (Gly) by two adenosine triphosphate (ATP)-dependent reactions catalysed by gamma- glutamylcysteine synthetase (γ–ECS) and glutathione synthetase (GS). GSH plays a role in biosynthetic pathways, detoxification of xenobiotics and antioxidant chemistry. Moreover, this compound protects plants against oxidative stress and also acts as a storage and transport form of reduced sulfur. The accumulation of glutathione was observed in different plants exposed to various stress such as salinity, drought, extreme temperatures (cold and heat), UV light, herbicides and air pollutants. Abiotic stress often causes a series of morphological, physiological, biochemical and molecular changes that unfavorably affect plant growth, development and productivity.

Major Phytohormones Under Abiotic Stress

Plants have evolved numerous mechanisms to cope with abiotic stresses such as salinity, drought, high temperatures, chilling, heavy metal stress as well as UV or mechanical wounding. To survive in unfavorable conditions, plants have developed perception of external signals which leads to induction of defense mechanisms. Abiotic stress conditions, individually or in combination, require a set of specific acclimation responses, tailored to the definite needs of the plant, and a combination of two or more different stresses might require a response that is also equally specific. Phytohormones are essential for the ability of plants to adapt to changing environments, by mediating growth, development, nutrient allocation, and source/sink transitions. The phytohormones engaged in the defense responses to abiotic stresses are abscisic acid (ABA), ethylene (ET), auxin (IAA), gibberellic acid (GA), cytokinins (CKs), jasmonic acid (JA), salicylic acid (SA), brassinosteroids (BRs), and polyamines (PAs). Much evidence has implicated the key role of ABA, ET, IAA, CKs, JA, and SA in plant signaling pathways in plant responses to abiotic stresses, whereas the defensive mechanisms induced by some phytohormones, such as GA, BRs, and PAs, are less well studied. Phytohormones function as signal molecules in regulation of the expression of defensive genes and modification of enzyme activity. These phytohormones can act separately or coordinate with other signaling pathways in a complex network. Cross-talk between the different hormones results in synergetic or antagonistic interactions that play crucial roles in the response of plants to abiotic stress.

Participation of Phytohormones in Adaptation to Salt Stress

Salt stress is one of the major abiotic stresses limiting productivity and quality of agricultural crops. The adverse effects concern germination, plant vigor, and crop yield in arid and semiarid regions. Most crops are salinity sensitive or even hypersensitive and they are described as glycophytes. In contrast, high salinity is tolerated by halophytes, which are present in very small numbers, accounting for approx. only 1 % of the world’s flora. Glycophytes develop some adaptation mechanisms to monitor salt stress and regulate plant physiology and metabolism in order to cope with this stress. Phytohormones are recognized as vital agents in the adaptation process during salt stress. Plant hormones including abscisic acid, salicylic acid, jasmonic acid, ethylene, brassinosteroids, and the others can regulate that cross talk and responses to salt stress. Molecules, such as transcription factors and MAP kinases, are main agents involved in stress signaling pathways and phytohormone cross talk. This chapter provides an explanation of the salt stress mechanism, while salt stress tolerance and the roles of different plant hormones are presented. The effects of endogenous and exogenous phytohormones on adaptation to salt stress are characterized.

The effect of fertiliser treatments on the severity of Fusarium head blight and mycotoxin biosynthesis in winter rye

Abstract The fungi of the genus Fusarium cause Fusarium head blight (FHB), a devastating disease that reduces grain yield and quality. They also produce mycotoxins which may pose a serious threat to human and animal health. This study investigated the effects of NPK fertilisation, foliar application of Cu, Zn, and Mn, applied separately and in combination, and of the Nano-Gro® organic growth stimulator on the occurrence of FHB in cultivar Dańkowskie Diament rye based on the mycological analysis of kernels and on the concentrations of Fusarium mycotoxins in grain. The severity of FHB caused by seven species of the genus Fusarium was influenced by weather conditions in the analysed growing seasons. The applied fertilisation and the Nano-Gro® organic growth stimulator exerted varied effects on FHB development and the biosynthesis of Fusarium mycotoxins (deoxynivalenol, nivalenol, zearalenone and fumonisins) in grain. The greatest reduction in deoxynivalenol and nivalenol concentrations was noted in 2013, and the levels of moniliformin were lower in treated samples than in absolute control (untreated) samples in both years of the study. The severity of FHB positively correlated with the concentrations of zearalenone, deoxynivalenol, nivalenol, and moniliformin in the grain samples. Greater accumulation of ergosterol was noted in the rye grain harvested in 2013 than in 2012, and fertiliser treatment led to higher ergosterol concentrations than did control treatment.

ABA: Role in Plant Signaling Under Salt Stress

Salt stress in soil and water is one of the primary abiotic stresses which limit plant growth and productivity, especially in arid and semi-arid regions. Salinity is responsible for other stresses such as ion toxicity, and nutrient imbalances. During the development of salt stress within the plant, all the major processes such as photosynthesis, protein synthesis, energy and lipid metabolisms are affected. In terms of salinity tolerance, plants are classified as halophytes, which can grow and reproduce under high salinity (>400 mM NaCl), and glycophytes, which cannot survive high salinity. Most of the grain crops and vegetables like bean, eggplant, corn, potato and sugarcane are natrophobic (glycophytes) and are highly susceptible to soil salinity.