Literature Review on the Effects of Heavy Metal Stress and Alleviating Possibilities through Exogenously Applied Agents in Alfalfa (Medicago sativa L.)

Heavy metals (HMs) are among the most important toxic agents since they reach the soil through various routes and accumulate in the food chain. Therefore, HMs induce problems in soil integrity and in plant, animal, and human health. Alfalfa (Medicago sativa L.) is a significant crop worldwide, utilized in animal production. Furthermore, because of its nitrogen-absorbing ability via symbiotic strains of bacteria, it increases soil productivity. However, there are relatively few studies investigating the effects of HMs and their alleviation possibilities on alfalfa plants. Therefore, the goal of this review is to clarify the current state of research into HM-induced alterations in alfalfa and to determine the extent to which externally applied microorganisms and chemical compounds can mitigate the negative effects. The aim is to indicate areas of development towards further understanding of HM detoxification in alfalfa and to identify future research directions.

Effect of cadmium stress on certain physiological parameters, antioxidative enzyme activities and biophoton emission of leaves in barley (Hordeum vulgare L.) seedlings

Biophoton emission is a well-known phenomenon in living organisms, including plant species; however, the underlying mechanisms are not yet well elucidated. Nevertheless, non-invasive stress detection is of high importance when in plant production and plant research. Therefore, the aim of our work was to investigate, whether biophoton emission is suitable for the detection of cadmium stress in the early phase of stress evolution and to identify certain stress-related events that occur rapidly upon cadmium exposure of barley seedlings parallel to biophoton emission measurements. Changes of biophoton emission, chlorophyll content estimation index, ascorbate level, the activity of ascorbate- and guaiacol peroxidase enzymes and lipid oxidation were measured during seven days of cadmium treatment in barley (Hordeum vulgareL.) seedlings. The results indicate that the antioxidant enzyme system responded the most rapidly to the stress caused by cadmium and the lipid oxidation-related emission of photons was detected in cadmium-treated samples as early as one day after cadmium exposure. Furthermore, a concentration-dependent increase in biophoton emission signals indicating an increased rate of antioxidative enzymes and lipid oxidation was also possible to determine. Our work shows evidence that biophoton emission is suitable to identify the initial phase of cadmium stress effectively and non-invasively.

Restoration of photosystem II photochemistry and carbon assimilation and related changes in chlorophyll and protein contents during the rehydration of desiccated Xerophyta scabrida leaves

Recovery of photosynthesis in rehydrating desiccated leaves of the poikilochlorophyllous desiccation-tolerant plant Xerophyta scabrida was investigated. Detached leaves were remoistened under 12 h light/dark cycles for 96 h. Water, chlorophyll (Chl), and protein contents, Chl fluorescence, photosynthesis-CO(2) concentration response, and the amount and activity of Rubisco were measured at intervals during the rehydration period. Leaf relative water contents reached 87% in 12 h and full turgor in 96 h. Chl synthesis was slower before than after 24 h, and Chla:Chlb ratios changed from 0.13 to 2.6 in 48 h. The maximum quantum efficiency recovered faster during rehydration than the photosystem II operating efficiency and the efficiency factor, which is known to depend mainly on the use of the electron transport chain products. From 24 h to 96 h of rehydration, net carbon fixation was Rubisco limited, rather than electron transport limited. Total Rubisco activity increased during rehydration more than the Rubisco protein content. Desiccated leaves contained, in a close to functional state, more than half the amount of the Rubisco protein present in rehydrated leaves. The results suggest that in X. scabrida leaves Rubisco adopts a special, protective conformation and recovers its activity during rehydration through modifications in redox status.