The effect of salicylic acid(SA) on antioxidant system and protective mechanisms against UV-B induced oxidative stress was investigated in cucumber(Cucumis sativus L.) leaves. UV-B radiation and SA were applied separately or in combination to first leaves of cucumber seedlings, and dry matter accumulation, lipid peroxidation and activities of antioxidant enzymes were measured in both dose and time-dependant manner. UV-B exposure showed reduced levels of fresh weight and dry matter production, whereas SA treatment significantly increased them. SA noticeably recovered the UV-B induced inhibition of biomass production. UV-B stress also affected lipid peroxidation and antioxidant enzyme defense system. Malondialdehyde(MDA), a product of lipid peroxidation, was greatly increased under UV-B stress, showing a significant enhancement of a secondary metabolites, which may have antioxidative properties in cucumber leaves exposed to UV-B radiation. Combined application of UV-B and SA caused a moderate increase in lipid peroxidation. These results suggest that SA may mediate protection against oxidative stress. UV-B exposure significantly increased SOD, APX, and GR activity compared with untreated control plants. Those plants treated with 1.0 mM SA showed a similar pattern of changes in activities of antioxidant enzymes. SA-mediated induction of antioxidant enzyme activity may involve a protective accumulation of H2O2 against UV-B stress. Moreover, their activities were stimulated with a greater increase by UV-B+SA treatment. The UV-B+SA plants always presented higher values than UV-B and SA plants, considering the adverse effects of UV-B on the antioxidant cell system. ABA and JA, second messengers in signaling in response to stresses, showed similar mode of action in UV-B stress, supporting that they may be important in acquired stress tolerance. Based on these results, it can be suggested that SA may participates in the induction of protective mechanisms involved in tolerance to UV-B induced oxidative stress.

In Korea, chilli pepper (Capsicum annum L.) is a major vegetable crop. The pepper seed market is about $35 million and the whole sale market including processed products is equivalent to $2 billion, representing the second highest market value among crops, next to rice in Korea. Since the development of elite pepper variety is so competitive, vegetable seed companies usually run two important programs to keep the credibility of seed quality. One program is to deliver F1 hybrid seeds with a high purity test to farmers. The purity control of parents and F1 hybrid to avoid any contamination is conducted by DNA markers because pepper seeds are obtained using MS line. The other program is to identify the F1 variety from other varieties by analyzing the polymorphism so that the company and/or breeder protects the intellectual property from copying by others or from non-intentional contamination. We have developed about 900 EST-SSR sets from pepper and used to both programs. A total of 66 markers were selected to identify 32 F1 varieties and their own parents. Using these markers, the purity control of F1 hybrid rose up to the highest degree. We also found several SSR markers to distinguish F1 variety from other varieties and these markers could be useful to find the uniqueness of F1 cultivar.

Tocopherol belongs to the Vitamin E class of lipid soluble antioxidants that are essential for human nutrition. Tocopherols consist of a chromanol ring and a 15-carbon tail derived from homogentisate (HGA) and phytyl diphosphate, respectively. Condensation of HGA and phytyl diphosphate, the committed step in tocopherol biosynthesis, is catalyzed by HGA phytyltransferase (HPT). To increase tocopherol level in cucumber fruit, we performed Agrobacterium-mediated transformation with mdhpt gene, encoding HPT, isolated from apple (Malus domestica). We obtained two independent T0 cucumber plants from transforming 2,142 explants. Southern blot analysis of T0 showed that mdhpt was inserted in the genome. In order to test the tocopherol level, T1 cucumber fruits were screened by GC analysis. From 39 T1 fruits tested, some fruits showed 1.5-2 fold in α- and β-tocopherol content comparing to control. However, most of fruits contained lower levels of γ- and δ- tocopherol indicating a partition of metabolites in tocopherol biosynthesis pathway. We selected these T1 line and made a self-cross to obtain T2 seeds.