Abstract
The aim of the present study was to describe eggplant (<i>Solanum melongena</i> L.) tolerance to stress factors in the seedling stage as a basis for future studies on cross-tolerance to other stressors in subsequent stages of growth. After germination (3 days / 26<sup>o</sup>C), ‘Epic F<sub>1</sub>’ seedlings were exposed to chilling stress (3, 6 and 9<sup>o</sup>C × 48 h<sup>-1</sup>), heat stress (35, 40 and 45<sup>o</sup>C × 2 h<sup>-1</sup>), osmotic stress (mannitol 0.2; 0.6 and 1.0 M x 2 h<sup>-1</sup>), and oxidative stress (H<sub>2</sub>O<sub>2</sub> 0.2; 0.4 and 0.6 M × 2 h<sup>-1</sup>). A linear measurement of seedling radicle growth, electrolyte leakage and external symptoms of radicle damage under the stress conditions, compared to the non-stressed control, were analyzed. It was found that stressors in all experimental combinations caused a morphological and physiological response from eggplant seedlings. A significant reduction in linear growth of radicles, showed as an absolute length and as a percentage of the control, was found in the treatments exposed to chilling stress (3 and 6<sup>o</sup>C), heat stress (35, 40 and 45<sup>o</sup>C), osmotic stress (0.2, 0.6 and 1.0 M mannitol) as well as oxidative stress (0.2, 0.4 and 0.6 M H<sub>2</sub>O<sub>2</sub>). The changes in seedling length as a result of stress factors did not always correspond with the changes in seedling mass. Electrolyte leakage in the treatments exposed to the following stressors: 3 and 6<sup>o</sup>C as well as 0.6 M H<sub>2</sub>O<sub>2</sub>, was significantly greater than that observed in control plants. Based on the obtained results and microscopic observations of radicle damage, the following stressors can be identified as those which cause a physiological response without severe damage: 9<sup>o</sup>C × 48 h<sup>-1</sup> (chilling stress), 35<sup>o</sup>C × 2 h<sup>-1</sup> (heat stress), 0.2 M mannitol × 2 h<sup>-1</sup> (osmoticum), and H<sub>2</sub>O<sub>2</sub> 0.2 M × 2 h<sup>-1</sup> (oxidation factor). We propose these stressors as a basis for future studies on plant acclimation and hardening to other stresses.
Highlights
Warm climate plant species like eggplant, grown in the temperate climate zone, are subjected to environmental stress which limits crop productivity, its quality, and post-harvest life
A significant reduction in linear growth of radicles, showed as an absolute length and as a percentage of the control, was found in the treatments exposed to chilling stress (3 and 6oC), heat stress (35, 40 and 45oC), and osmotic stress (0.2, 0.6 and 1.0 M mannitol) as well as oxidative stress (0.2, 0.4 and 0.6 M H2O2) – Figs 1 and 2
Seedlings treated with increased solutions of mannitol and H2O2 showed a commensurate reduction in radicle growth (Fig. 2A, 2B)
Summary
Warm climate plant species like eggplant, grown in the temperate climate zone, are subjected to environmental stress which limits crop productivity, its quality, and post-harvest life. The primary sensor of physical stress is a cell membrane, because a direct reduction in its liquidity is observed (Chinnusamy et al 2006). Biochemical and physiological acclimation leads to cell membrane stiffening and reorganization of microfilaments which may be followed by activation of Ca2+ channels and an increased cytosolic Ca2+ level Low temperature causes oxidative stress, and in this case the plant protection strategy is to increase the synthesis of antioxidants (i.e. glutathione, ascorbate, carotenoids, flavonoids, polyphenols, tocopherols) and of specialized enzymes decomposing reactive oxygen species, i.e. superoxide dismutase, catalase, peroxidase, and the enzymes involved in Agnieszka Sękara, Renata Bączek-Kwinta, Andrzej Kalisz, Stanisław Cebula glutahione metabolism (Bartosz , 1997; Bączek - Kwinta et al 2005; Bączek - Kwinta and Kościelniak , 2009)
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