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Liu XiaoYing, Guo ShiRong, Xu ZhiGang, Jiao XueLei and Takafumi Tezuka

The chloroplast structural alteration and the photosynthetic apparatus activity of cherry tomato seedlings were investigated under dysprosium lamp [white light control (C)] and six light-emitting diode (LED) light treatments designated as red (R), blue (B), orange (O), green (G), red and blue (RB), and red, blue, and green (RBG) with the same photosynthetic photon flux density (PPFD) (≈320 μmol·m−2·s−1) for 30 days. Compared with C treatment, net photosynthesis of cherry tomato leaves was increased significantly under the light treatments of B, RB, and RBG and reduced under R, O, and G. Chloroplasts of the leaves under the RB treatment were rich in grana and starch granules. Moreover, chloroplasts in leaves under RB seemed to be a distinct boundary between granathylakoid and stromathylakoid. Granathylakoid under treatment B developed normally, but the chloroplasts had few starch granules. Chloroplasts under RBG were similar to those under C. Chloroplasts under R and G were relatively rich in starch granules. However, the distinction between granathylakoid and stromathylakoid under R and G was obscure. Chloroplasts under O were dysplastic. Palisade tissue cells in leaves under RB were especially well-developed and spongy tissue cells under the same treatment were localized in an orderly fashion. However, palisade and spongy tissue cells in leaves under R, O, and G were dysplastic. Stomatal numbers per mm2 were significantly increased under B, RB, and RBG. The current results suggested blue light seemed to be an essential factor for the growth of cherry tomato plants.

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Chang-Xia Du, Huai-Fu Fan, Shi-Rong Guo and Takafumi Tezuka

To examine whether spermidine (SPD) modifies plant antioxidant enzyme expression in response to short-term salt stress, cucumber (Cucumis sativus) seedlings were treated with NaCl in the presence or absence of SPD for 3 days. Compared with untreated control plants, free radical production and malondialdehyde content in leaves and roots increased significantly and plant growth was suppressed under 50 mm NaCl stress. Exogenous SPD sprayed on leaves at a concentration of 1 mm alleviated salinity-mediated growth reduction. Salt stress caused a consistent increase in soluble protein content, as well as peroxidase (POD) and superoxide dismutase (SOD) activities in cucumber seedlings. By native polyacrylamide gel electrophoresis, five POD isozymes were detected in cucumber seedling leaves, and seven in roots. We detected five SOD isozymes in leaves and four in roots, and two catalase (CAT) isozymes in leaves and two in roots. Our results indicate that salt stress induced the expression of POD and SOD isozymes in cucumber seedlings, but inhibited the expression of CAT isozymes in roots. Application of exogenous SPD further increased POD and SOD expression and activity, and led to the differential regulation of CAT in leaves and roots. These data show that antioxidant enzymes, especially POD and SOD, appear to protect cucumber seedlings against stress-related damage, and they appear to function as the molecular mechanisms underlying the response of cucumber seedlings to salinity. Moreover, SPD has potential to scavenge directly free radical and to alleviate growth inhibition and promote the activity and expression of antioxidant system enzymes in cucumber seedlings under short-term salt stress.