The study examines the effect of acclimation on the antioxidant system and proline metabolism in cucumber leaves subjected to 100 and 150 NaCl stress. The levels of protein carbonyl group, thiobarbituric acid reactive substances, α-tocopherol, and activity of ascorbate and glutathione peroxidases, catalase, glutathione S-transferase, pyrroline-5-carboxylate: synthetase and reductase as well as proline dehydrogenase were determined after 24 and 72 h periods of salt stress in the acclimated and non-acclimated plants. Although both groups of plants showed high α-tocopherol levels, in acclimated plants was observed higher constitutive concentration of these compounds as well as after salt treatment. Furthermore, the activity of enzymatic antioxidants grew in response to salt stress, mainly in the acclimated plants. In the acclimated plants, protein carbonyl group levels collapsed on a constitutive level and in response to salt stress. Although both groups of plants showed a decrease in proline dehydrogenase activity, they differed with regard to the range and time. Differences in response to salt stress between the acclimated and non-acclimated plants may suggest a relationship between increased tolerance in acclimated plants and raised activity of antioxidant enzymes, high-level of α-tocopherol as well, as decrease enzyme activity incorporates in proline catabolism.

The effects of l-phenylalanine (PHE) on cell growth and production of shikonin and its derivatives, acetylshikonin (ACS) and isobutyrylshikonin (IBS), in suspension cultures of Arnebia euchroma were examined. Supplementing media using PHE have been successfully utilized to enhance shikonin production in cell cultures of other species of Boraginaceae. l-Phenylalanine, the key compound in the phenylpropanoid pathway, is converted by phenylalanine ammonia lyase (PAL) to trans-cinnamic acid, which is the precursor of p-hydroxybenzoic acid (PHB). Coupling of PHB and geranyl pyrophosphate (derived from mevalonate pathway) by p-hydroxybenzoate-m-geranyltransferase leads later to biosynthesis of shikonins. The addition of 0.01 or 0.1 mM PHE to the culture medium stimulated cell proliferation, where the highest observed increase in fresh cell biomass (measured as a ratio of final weight to initial weight) was 12-fold, in contrast to an eightfold increase in control cultures. Whereas, growth media supplemented with 1 mM PHE markedly reduced the rate of cell growth (to only twofold). Precursor feeding had detrimental effects on both ACS and IBS production in all PHE-supplemented media. The highest total content (intracellular + extracellular) of the investigated red pigments (9.5 mg per flask) was detected in the control culture without PHE. ACS was the major component of the naphthoquinone fraction determined in cells and post-culture media. Shikonin itself was found only in the post-culture media from cultures supplemented with 0.01 or 0.1 mM PHE. Increases in PAL activity corresponded well with the accumulation of investigated naphthoquinones in control culture. However, peak PAL activity did not directly correlate with maximum production of shikonin derivatives. Cytotoxicity of extracts, prepared from the cells cultivated in the presence of PHE or in control cultures, was tested on three cancer cell lines: HL-60, HeLa, and MCF-7. The extracts prepared from the untreated control cultures proved to be the most potent against the examined cancer cell lines. The mean inhibitory concentration values were 0.3, 13, and 8 μg ml⁻¹ for the HL-60, HeLa, and MCF-7 cells, respectively.

The study examines the effect of acclimation on carbon and nitrogen metabolism in cucumber leaves subjected to moderate and severe NaCl stress. The levels of glucose, sucrose, NADH/NAD⁺-GDH, AspAT, AlaAT, NADP⁺-ICDH, G6PDH and 6GPDH activity were determined after 24 and 72 hour periods of salt stress in acclimated and non-acclimated plants. Although both groups of plants showed high Glc and Suc accumulation, they differed with regard to the range and time of accumulation. Acclimation to salinity decreased the activities of NADP⁺-ICDH and deaminating NAD⁺-GDH compared to controls; however, these enzymes, together with the other examined parameters, showed elevated values in the stressed plants. The acclimated plants showed higher G6PDH activity than the non-acclimated plants, whereas both groups demonstrated similar 6PGDH activity. The high activities of NADH-GDH, AlaAT and AspAT observed in the examined plants could be attributed to a high demand for glutamate. The observed changes may be required for the maintenance of correct TCA cycle activity, and acclimation appeared to positively influence these adaptive processes.

In the present study, we measured the markers of oxidative stress as well as activity of antioxidative enzymes and content of α-tocopherol in the acclimated and non-acclimated cucumber (Cucumis sativus L.) cell suspension cultures su...