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Many tobacco (Nicotiana tabacum) cultivars are salt-tolerant and thus are potential model plants to study the mechanisms of salt stress tolerance. The CALCINEURIN B-LIKE PROTEIN (CBL) is a vital family of plant calcium sensor proteins that can transmit Ca2+ signals triggered by environmental stimuli including salt stress. Therefore, assessing the potential of NtCBL for genetic improvement of salt stress is valuable. In our studies on NtCBL members, constitutive overexpression of NtCBL5A was found to cause salt supersensitivity with necrotic lesions on leaves. NtCBL5A-overexpressing (OE) leaves tended to curl and accumulated high levels of reactive oxygen species (ROS) under salt stress. The supersensitivity of NtCBL5A-OE leaves was specifically induced by Na+, but not by Cl−, osmotic stress, or drought stress. Ion content measurements indicated that NtCBL5A-OE leaves showed sensitivity to the Na+ accumulation levels that wild-type leaves could tolerate. Furthermore, transcriptome profiling showed that many immune response-related genes are significantly upregulated and photosynthetic machinery-related genes are significantly downregulated in salt-stressed NtCBL5A-OE leaves. In addition, the expression of several cation homeostasis-related genes was also affected in salt-stressed NtCBL5A-OE leaves. In conclusion, the constitutive overexpression of NtCBL5A interferes with the normal salt stress response of tobacco plants and leads to Na+-dependent leaf necrosis by enhancing the sensitivity of transgenic leaves to Na+. This Na+ sensitivity of NtCBL5A-OE leaves might result from the abnormal Na+ compartmentalization, plant photosynthesis, and plant immune response triggered by the constitutive overexpression of NtCBL5A. Identifying genes and pathways involved in this unusual salt stress response can provide new insights into the salt stress response of tobacco plants.

Artemisinin, an antimalarial secondary metabolite produced in Artemisia species, also has been recognized as an allelochemical that inhibits the growth of several plant species. However, the phytotoxicity mechanism of artemisinin is not exhaustively deciphered up to now. In this research, the effects of artemisinin on Arabidopsis thaliana root gravitropic curvature and development were characterized. Exogenously applied artemisinin disturb the root gravitropic responses, inhibited the elongation of primary and lateral roots and root hairs in a concentration-dependent fashion, and prevented the formation of lateral roots and root hairs. Moreover, the number of starch grain and the distribution range of auxin in the root tip was reduced by artemisinin, and the redistribution of auxin was less sensitive to gravity stimulus when treated with artemisinin than that of control. The expression of auxin transporter PIN2 was partially suppressed by artemisinin. Together, the results demonstrated that the effects of artemisinin on root gravitropism and root system development were largely dependent on the reduction of starch grain and auxin levels, as well as the disordered lateral auxin redistribution.

2-Phenylethanol (2-PE) is an aromatic alcohol with a rose-like odour, which is widely used in the food, drink and cosmetic industry. It also present in cigarette aromas. As a unique renewable biomass, tobacco contains abundant aromatic compounds, but is rarely used as a feedstock for synthesizing bio-based products. In this study, it was found that 2-PE can be produced from tobacco waste by Saccharomyces cerevisiae. Plackett-Burman design, steepest ascent design and Box-Behnken designs were applied to optimize the fermentation bioprocess, and the maximum titre of 2-PE reached 1.55 g/l. The study explored a new method of 2-PE production and also provided a valuable way to utilize tobacco waste.

Stellera chamaejasme, a perennial weed which is an ecological threat, is widely distributed in some grasslands of Central and Eastern Asia. Our previous studies have identified several allelochemicals including two coumarins (umbelliferone and daphnoretin), from S. chamaejasme, and confirmed that allelopathy contributed to the competitive behavior of this weed. In this study, the inhibitory effects of umbelliferone and daphnoretin on lettuce seedlings and the mechanisms of their phytotoxicity were investigated. Results showed that shoot and root elongation and fresh weight of lettuce seedlings were effectively inhibited by umbelliferone in a concentration-dependent manner. Daphnoretin showed a weaker phytotoxicity. Both of the coumarins arrested the mitosis process in lettuce root tips and induced proline overproduction. Additionally, loss of cell viability and overproduction of reactive oxygen species in lettuce root cells were found after treatments with umbelliferone. Moreover, umbelliferone caused lipid peroxidation. These results suggested that umbelliferone displayed stronger phytotoxicity than daphnoretin on lettuce growth, and that the two coumarins had different mechanisms of phytotoxicity. That of daphnoretin was mainly dependent on its inhibitory effects on mitosis. Umbelliferone caused membrane lipid peroxide formation and cell death by inducing ROS overproduction, and impacted cell division, which resulted in growth inhibition of the receptor plant.