Melatonin (ML) is an indolamine that regulates a wide range of physiological processes as growth of roots and shoots, antioxidant enzyme activity, seed germination, photosynthetic efficiency promoting stress tolerance in plants, mitigating the harmful effects of abiotic stress. Effects of pretreatment of soybean (Glycine max (L.) Merr.) seeds with 10, 30, 60 and 90 μM ML were evaluated in seedlings under osmotic stress measuring germination speed index, and root protrusion, growth, and DM. Under osmotic stress, ML increased germination speed index at 10 (239%), 30 (194%) and 60 μM ML (189%); 5 th -day root protrusion by 290%, 214%, 185% and 85% (10, 30, 60, and 90 μM ML respectively). The application of 10 (328%), 30 (224%), 60 (265%), 90 μM ML (129%) increased root length, followed by root DM in stressed seedlings. Drought stress reduced photosynthetic efficiency, increased ROS, and reduced antioxidant enzymatic activities in soybean. In a second experiment, well-watered (100% field capacity) (WW) and drought stressed (DS) soybean plants received 30 and 50 μM ML. Melatonin increased rate of CO2 assimilation and net photosynthetic rate at 30 μM ML (WW) in 28% (2 d after application) and 50 μM ML (DS) in 48% (5 d after application). Melatonin increased antioxidant enzymes activity (catalase and peroxidase) in plants under drought stress. The ML application enhanced leaf area in WW plants, however decreased in stressed plants. An increased number of seeds, pod numbers, total seed mass, root DM were observed under WW. Drought stress increased numbers of seeds (27%), pod numbers (33%) and total seeds mass (27%) with 30 μM ML. These results demonstrated that ML mitigated negative effects produced by drought on germination and growth of soybean seedlings, and acted as a drought tolerance inducer, improving yield under stress condition.
Plants can develop differentially because of their ability of self/nonself discrimination and the degree of kinship among them. Here, we evaluate the ability of self/nonself discrimination of Eucalyptus urophylla S.T. Blake roots in plant groups with different levels of relatedness. We used three plant groups: clonal, half-siblings, and population. Split-root plants were grown in pots containing either two roots of the same plant (SD) or of two different plants (NSD). The growth of root and leaves of the half-siblings and population plants was decreased in NSD in relation to SD, whereas this response was not observed in the clonal group. The multivariate analysis indicated that there was a progressive increase in plant responses likely caused by competitive interaction of roots, as the level of relatedness between individuals was lower. Our results suggest that the group of clonal plants minimized the competitive interaction among them, indicating low ability to discriminate from each other. However, half-sibling and populational plants reduced growth as a result of root competition, showing high capacity of self discrimination. Thus, a minimum degree of genetic variation between plants seems necessary for kin recognition to be expressed.
Aim of study: Soils contaminated by heavy metals, such as cadmium, may reduce plant development. Exogenous application of plant growth regulators (PGR), are used for optimizing the crops production in stressful environments. The aim of this study was to evaluate the effects of Cd concentrations on the development of soybean seedlings under exogenous application of a commercial PGR.Area of study: Presidente Prudente, São Paulo, Brazil.Material and methods: Soybean seeds were pre-treated in distilled water (control treatment) and in solution with plant growth regulator (PGR treatment) and then germinated with distillated water. The germinated seeds were transferred to different levels of Cd (0, 100, 500 and 900 mg of Cd).Main results: Cd exposure at increasing concentrations, decreased root development, (area, length and volume of roots) and activity of enzymatic antioxidants (SOD, CAT and APX) and enhanced MDA. These responses were accentuated by the PGR exposition. The root morphology and activity of antioxidant enzymes presented "hormesis" responses until 500 mg L-1 of Cd, and the proline content may have played a fundamental role in the maintenance of metabolic activities and biomass.Research highlights: The results indicate that the use of PGR intensified the toxicity responses caused by exposure to increased Cd level. In addition, stress indicators such as MDA content and antioxidant activity in different organs (root and shoot) of soybean seedlings, responded differently according with the use of PGR under exposure of Cd.
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