Priming may be an efficient pre-treatment of plants in order to enhance their ability to cope with unfavourable growth conditions, and to improve defensive metabolism through elevated levels of protective substances which may also act as health-promoting agents upon human consumption. The aim of this work was to evaluate the beneficial influence of priming with the naturally occurring, but scarcely known vitamin U (S-methylmethionine) on cold stress tolerance of lettuce (the frequently grown ‘May King’ cultivar). Effects on germination, photosynthetic efficiency, as well as on health-promoting carotenoid and vitamin C contents were investigated. Photosynthetic capacity, strongly related to productivity, was evaluated with parameters of induced chlorophyll fluorescence and of leaf gas exchange through stomata, using plants grown in hydroponic cultures. Priming with vitamin U significantly compensated for the delaying effect of low temperature (5 °C) on seed germination, as well as for inhibition of light-converting photochemical reactions and of carbon dioxide assimilation by cold stress. Use of vitamin U to prime lettuce plantlets for low temperature stress resulted in an elevated content of carotenoid pigments and of vitamin C in leaves, which improve the quality of consumed lettuce with respect to the health-promoting capacity. This beneficial influence of vitamin U was not proportional with its concentration (2 mM had no stronger effects than 0.25 mM), so small amounts of this substance were sufficient for a sustained efficiency in promoting hardening against chilling temperatures. This is the first report on priming of lettuce for cold tolerance by using S-methylmethionine (vitamin U), with a possible application in improvement of crop quality and productivity.   ********* In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 3, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue. *********

ABSTRACT. The aim of the study is to evaluate the suitability of a local strain of the microalga Scenedesmus opoliensis in remediation of water pollution with different amounts of chromium(VI), and also to identify new biochemical and physiological markers for a more reliable indication of sustainability and efficiency of bioextraction and phytoaccumulation processes. Quantitative analysis of photosynthetic pigments reveals that the chlorophylls to carotenoids ratio is a sensitive marker of chromium toxicity and of algal metal tolerance on which the remediative capacity relies. From among the chlorophyll fluorescence parameters, the Fv/Fm ratio, related to potential quantum yield of photochemical reactions, indicates that alkaline pH of the medium (8.65-9.15) favors algal vitality as compared to acidic conditions with pH values around 5. The highest extraction rate (91%) is achieved upon exposure of algae for one week to lower chromium concentrations (5 µM) in alkaline water environment, and a longer exposure time does not increase bioaccumulation. These results may directly contribute to optimization of remediation technology for chromium-polluted water, providing new markers and a new algal strain to be introduced in wastewater treatment.

ABSTRACT. The aim of the study is to compare biochemical and physiological reactions of two related species of green microalgae (Scenedesmus acuminatus and Scenedesmus opoliensis), both considered suitable for bioindication and remediation of aquatic environments polluted with herbicides. Monoalgal axenic cultures were treated for 10 days under controlled conditions with different concentrations (from 0.1 μM to 100 µM) of glufosinate (a nonselective contact herbicide that inhibits glutamine synthase activity, thus disturbing photorespiration, inhibiting photosynthetic carbon assimilation, and generating ammonium excess in plant cells). S. opoliensis was found to be a better indicator of adverse effects of glufosinate than S. acuminatus. Changes in the ground chlorophyll fluorescence (reflecting light energy harvesting capacity), in cell division rate and in chlorophyll-a content may be early, costeffective and sensitive markers of herbicide impact on microalgal communities inhabiting polluted water. Our results bring new data concerning the need of selection among related test organisms based on differentiated tolerance, as well as concerning biochemical parameters suitable for evaluation of water pollution impact when organic xenobiotics accumulate in aquatic environments. Thus, the presented results may be applied in optimizing bioindication of water quality using microalgae, and in treatment of wastewater polluted due to agricultural practices.