For C. vulgaris and L. boryana, the maximum activity

was reached in the third day of incubation, while for K. flaccidum and C. reinhardtii, maximum activity was achieved in the first day. C. vulgaris had the highest activity, followed in descending order by L. boryana, C. reinhardtii, and K. flaccidum. The differences in POD activity among the species were significant (P < 0.05). Proline levels in treated cells were related to the PEG concentrations treated (Fig. S4 in the Supporting Information). An elevation of proline levels was observed when cells were treated with 25% PEG (Fig. 4A), with variable dynamics among the species. L. boryana cancer metabolism inhibitor had higher intracellular proline levels during the first 2 days of treatment with 25% PEG, whereas the highest levels in C. vulgaris occurred after 3 days. Significantly, the elevation

in proline levels were higher (i.e., 5-to 10-fold) in these two drought-tolerant species, when compared to the non-tolerant species (2- to 3-fold), namely K. flaccidum and C. reinhardtii. For L. boryana and K. flaccidum, the highest proline level was reached in the second day of incubation SB203580 in vivo and then the level declined, whereas increasing proline levels were observed for C. vulgaris and C. reinhardtii until the end of incubation (day 7; Fig. 4A). After treatment with PEG, protein content in L. boryana cells increased considerably, while in C. vulgaris, the concentration increased only slightly (Fig. 4B). In contrast, the protein content in C. reinhardtii and K. flaccidum declined with incubation time. The magnitude of increased protein content was positively correlated with the degree of tolerance to drought stress induced by PEG. Under 15% PEG, the changes in intracellular carotenoids content in C. reinhardtii (from 2.7 [the control] to 3.3 mg · g−1 dr.wt.) and in K. flaccidum (from 2.1 to 2.5 mg · g−1 dr.wt.) were quite low, when compared with C. vulgaris (from 4.2 to 8.8 mg · g−1 dr.wt.) and L. boryana (from 2.2 to 5.9 mg · g−1 dr.wt.). Apparently, a remarkable increase up to 2- to 3-fold occurred in the latter two species. Under 25% PEG, the carotenoids content in L. boryana increased from 2.2 to 7.1 mg · g−1

dr.wt., while in other three species declined with increasing incubation time (Fig. 4C). The concentrations of PC and APC in L. boryana selleck inhibitor cells decreased during treatment with 25% PEG, from 45.6 to 33.7 mg · g−1 and from 33.6 to 26.2 mg · g−1 dr.wt., respectively. Under treatment with 15% PEG, changes in the concentrations of PC and APC were insignificant, from 45.6 to 43.7 mg · g−1 and from 33.6 to 34.2 mg · g−1 dr.wt., respectively. The ratio of PC/APC also decreased in every treatment (Fig. 5) due to a faster decline of PC than APC. The results of Pearson correlation analysis showed that the cellular content of chl-a was correlated positively with that of carotenoids, and negatively with MDA and proline (P < 0.001; Table 1; Fig. S4).