Is leaf age a predictor for cold tolerance in winter oilseed rape plants?

Adjustments of the Phytochemical Profile of Broccoli to Low and High Growing Temperatures: Implications for the Bioactivity of Its Extracts

Climate change causes shifts in temperature patterns, and plants adapt their chemical content in order to survive. We compared the effect of low (LT) and high (HT) growing temperatures on the phytochemical content of broccoli (Brassica oleracea L. convar. botrytis (L.) Alef. var. cymosa Duch.) microgreens and the bioactivity of their extracts. Using different spectrophotometric, LC-MS/MS, GC-MS, and statistical methods, we found that LT increased the total phenolics and tannins in broccoli. The total glucosinolates were also increased by LT; however, they were decreased by HT. Soluble sugars, known osmoprotectants, were increased by both types of stress, considerably more by HT than LT, suggesting that HT causes a more intense osmotic imbalance. Both temperatures were detrimental for chlorophyll, with HT being more impactful than LT. HT increased hormone indole-3-acetic acid, implying an important role in broccoli's defense. Ferulic and sinapic acid showed a trade-off scheme: HT increased ferulic while LT increased sinapic acid. Both stresses decreased the potential of broccoli to act against H2O2 damage in mouse embryonal fibroblasts (MEF), human keratinocytes, and liver cancer cells. Among the tested cell types treated by H2O2, the most significant reduction in ROS (36.61%) was recorded in MEF cells treated with RT extracts. The potential of broccoli extracts to inhibit α-amylase increased following both temperature stresses; however, the inhibition of pancreatic lipase was increased by LT only. From the perspective of nutritional value, and based on the obtained results, we conclude that LT conditions result in more nutritious broccoli microgreens than HT.

Effects of heat stress on photosystem II activity and antioxidant enzymes in two maize cultivars

The main reason for the maize genotype "DKC7221" to be heat tolerant is to have higher photosynthetic activity under heat stress conditions. The genotype "P3167" is sensitive to high temperature because of the heat-induced inhibition in photosynthetic electron transport reactions. In the present study, the effect of heat stress (45 ºC for 20 min) on some physiological changes was investigated through a chlorophyll afluorescence technique, and some endogenous resistance mechanisms (activities of some antioxidant enzymes, free proline, and reduced ascorbate contents) in two maize cultivars (Zea mays L. cvs. P3167 and DKC7221). Chlorophyll fluorescence measurements demonstrated that heat stress led to the reduction in the efficiency of the Hill reaction, accumulation of inactive reaction centers, inhibition of electron flow from reaction centers to the plastoquinone pool, and induction of non-photochemical dissipation of absorbed light energy. Changes in Φo/(1 - Φo), SFI_ABS and PI_ABS indicated that electron transport reactions in P3167 were almost completely inhibited by heat stress. In DKC7221, however, photosynthetic electron transport reactions were maintained under heat stress conditions. As a result of impairment in the photosynthetic efficiency in P3167 under heat stress, oxidative stress appeared as shown by lower antioxidant activity, accumulation of H₂O₂, malondialdehyde, and formazon and photooxidative injuries in chlorophyll pigments in the leaf tissue. DKC7221, on the other hand, had a higher antioxidant efficiency and lower oxidative damage under heat stress. FeSOD activity was found to be responsible for the dismutation of superoxide radicals in both maize genotypes under heat stress. As a result, it may be concluded that the genotype DKC7221 is more tolerant to heat stress than P3167.