Blue and red lights differently regulate leaf photosynthesis. Previous studies indicated that plants under blue light generally exhibit better photosynthetic characteristics than those under red light. However, the regulation mechanism of related photosynthesis characteristics remains largely unclear. Here, four light qualities treatments (300 μmol m–2 s–1) including white fluorescent light (FL), blue monochromatic light (B, 440 nm), red monochromatic light (R, 660 nm), and a combination of red and blue light (RB, R:B=8:1) were carried out to investigate their effects on the activity of photosystem II (PSII) and photosystem I (PSI), and photosynthetic electron transport capacity in the leaves of cucumber (Cucumis sativus L.) seedlings. The results showed that compared to the FL treatment, the R treatment significantly limited electron transport rate in PSII (ETRII) and in PSI (ETRI) by 79.4 and 66.3%, respectively, increased non-light induced non-photochemical quenching in PSII (ΦNO) and limitation of donor side in PSI (ΦND) and reduced most JIP-test parameters, suggesting that the R treatment induced suboptimal activity of photosystems and inhibited electron transport from PSII donor side up to PSI. However, these suppressions were effectively alleviated by blue light addition (RB). Compared with the R treatment, the RB treatment significantly increased ETRII and ETRI by 176.9 and 127.0%, respectively, promoted photosystems activity and enhanced linear electron transport by elevating electron transport from QA to PSI. The B treatment plants exhibited normal photosystems activity and photosynthetic electron transport capacity similar to that of the FL treatment. It was concluded that blue light is more essential than red light for normal photosynthesis by mediating photosystems activity and photosynthetic electron transport capacity.

Root border cells (RBCs) originate from the root tip epidermis and surround the root apices. In this study, we evaluated the developmental characteristics and the roles of RBCs in protection of root apices of cucumber and fi gleaf gourd seedlings from CA toxicity. The formation of RBCs and the emergence of the root tip occurred almost simultaneously in root apices of cucumber and fi gleaf gourd seedlings. CA ranging from 0 to 0.25 mol L-1 inhibited root elongation and decreased root cell viability in the root tip, moreover the inhibitory effects of CA were more signifi cant in the CA-sensitive cucumber than in the CA-tolerant fi gleaf gourd. Removal of RBCs from root tips led to more severe CA induced inhibition of root elongation and decline in root cell viability. Increasing CA levels and treatment time decreased the relative viability of attached and detached RBCs. CA also induced a thicker mucilage layer surrounding attached RBCs of both species. Additionally, a signifi cantly higher relative cell viability of attached RBCs and thicker mucilage layers were observed in fi gleaf gourd. These results suggest that RBCs play an important role in protecting root tips from CA toxicity.