Study of the beneficial effects of green light on lettuce grown under short-term continuous red and blue light-emitting diodes

Red and blue light are the most important light spectra for driving photosynthesis to produce adequate crop yield. It is also believed that green light may contribute to adaptations to growth. However, the effects of green light, which can trigger specific and necessary responses of plant growth, have been underestimated in the past. In this study, lettuce (Lactuca sativa L.) was exposed to different continuous light (CL) conditions for 48 h by a combination of red and blue light-emitting diodes (LEDs) supplemented with or without green LEDs, in an environmental-controlled growth chamber. Green light supplementation enhanced photosynthetic capacity by increasing net photosynthetic rates (Pn), maximal photochemical efficiency (Fv/Fm), electron transport for carbon fixation (JPSII) and chlorophyll content in plants under the CL treatment. Green light decreased malondialdehyde and H2O2 accumulation by increasing the activities of superoxide dismutase (SOD; EC 1.15.1.1) and ascorbate peroxidase (APX; EC 1.11.1.11) after 24 h of CL. Supplemental green light significantly increased the expression of photosynthetic genes LHCb and PsbA from 6 to 12 h, and these gene expression were maintained at higher levels than those under other light conditions between 12 and 24 h. However, a notable down-regulation of both LHCb and PsbA was observed during 24 to 48 h. These results indicate that the effects of green light on lettuce plant growth, via enhancing activity of particular components of antioxidantive enzyme system and promoting of LHCb and PsbA expression to maintain higher photosynthetic capacity, alleviated a number of the negative effects caused by CL

The effect of salt stress on growth, chlorophyll content, lipid peroxidation and antioxidative enzymes of pumpkin seedling

Salinity is a major abiotic stress reducing the yield of a wide variety of crops all over the world. In order to investigate the antioxidant enzymes activity of four pumpkin genotypes (Iskenderun-4, AB-44, CU-7 and A-24) in response to salinity grown in hydroponic culture, 4 to 5 true leaf stages of pumpkin seedlings were subjected to 100 mM NaCl for 7 days. Salt stress induced changes in antioxidant enzymes, SOD, CAT, GR and APX, total chlorophyll content, lipid peroxidation and root and shoot fresh weight were measured. Salt treatment decreased root and shoots weight, chlorophyll content in salt sensitive genotypes more than salt tolerant genotypes. The four genotypes showed an increase in malondialdehyde (MDA) content under salt condition, but the increase in sensitive genotypes (CU-7 and A-24) were higher than that in salt tolerant genotypes (Iskenderun-4, AB-44). SOD, CAT, GR and APX activities increased salt stress. However these increases were higher in salt tolerant Iskenderun-4, AB-44 than salt sensitive CU-7 and A-24. These results indicate that pumpkin genotypes respond to salt induced oxidative stress by enzymatic defense systems