Kalopanaxpictus (Araliaceae) is a long-lived woody species primarily distributed throuBhout East Asia. This species isregarded as medically and ecologlcally important in Korea. We used starch gel electrophoresis to invesUgate its ailoz. yme variation and genetic structure in samples from Korean populations (both natural and cultivated). Our analysis of 10 enzymes revealed 18 loci, of which 10 were polymorphic (55.6%). Genetic diversity at the species and population levels were 0.200 and 0.149, respectively, with the mean for cultivated populations (0.124) being lower than for natural (wild) populations (0.181). Asexual and sexual reproduction modes, perennial habitat, and Iongevib/all were possible factors contributing to such high diversity. An indirect estimate of the number of migrants per generation (Nm : 1.08) indicated that gene flow was not extensive arnon 8 these Korean populations. Therefore, we suBgest that geographical distance as well as reproductive isolation between wild and cultivated plants may play roles in shaping the population structure of this species.

We studied how the relationship between cadmium (Cd) toxicity and oxidative stress influenced the Brm~th, photo.. synthetic efficiency, lipid peroxidation, and activity of ntimddative enzymes in the roots and leaves of rice (Oryza sat/va L Don~in). Plants were exposed to Cd for 21 d. Both seedling growth and photosynthetic efficiency decreased 8radu-ally with increasin 8 cadmium concentrations. Upid peroxi~ increased slowly in both roots and leaves, causing oxidative stress. However, each tissue type responded differentJy to Cd concentrations with regard to the induction/ inhibition of antioxidative enzymes. The acti~/of superoxide dismutase (SOD) increased in both roots and leaves. Ascorbate peroxidase (APX) activity increased in leaves treated with up to 0~5 I~l Cd, then decreased 8radually at higher concentrations. In contrast, APX activity in roots increased and remained constant between 0.25 and 25 pM Cd. Enhanced peroxidase (POD) activity was recorded for treatments with up to 25 ~ Cd, 8radually decreasing at higher concentrations in the leaves but remaining unchan~d in the roots. Catalase (CAT) activity increased in the roots, but decreased in the leaves, whereas the activity of 81utathione reductase (GR) was enhanced in both roots and leaves, where it remained elevated at higher Cd concentrations. These results susBest that.rice seedlinss tend to cope with free radicals bqmerated by Cd throush coordinated, enhanced activities of the antioxidative enzymes involved in detoxification.

We studied changes in biochemical and physiological status, level of oxidative damage, and antioxidant enzyme activities in detached leaves of cucumber plants (Cucumis sativus L. cv. Pyunggangnaebyungsamchuk) that were exposed to a low temperature (4~ Chlorophyll fluorescence (Fv/Fm) declined during the chilling treatment, but was slowly restored after the tissues were returned to 25~ Likewise, the fluorescence quenching coefficient and relative water content decreased during the stress period, but then increased during recovery. In contrast, we detected a significant rise in protein and hydrogen peroxide contents in the chilled leaves, as well as higher activities for superoxide dismutase, ascorbate peroxidase, peroxidase, and glutathione reductase. However, the level of catalase decreased not only during chilling but also after 24 h of recovery. These results indicate that exposure to low temperatures acts as an oxidative stress. Moreover, we propose that a regulating mechanism exists in the detached cucumber leaves and contains an antioxidant defense system that induces active oxygen species, thereby alleviating the effects of chilling stress within 12 h.

We photosynthetically characterized two rice cultivars -salt-sensitive ~Annapurna', and salt-tolerant 'Don~in' -growing under NaCI stress. Both cultivars showed an increase in Fo/Fm (the ratio of initial to maximal chlorophyll fluorescence) and a decrease in Fv/Fm (an indicator of the photochemical efficiency of PS II). In particular, the Fv value for Annapurna significant declined while FJFm was enhanced when plants were exposed to salt stress for 4 d. Annapurna also exhibited more rapid decreases in the coefficients for photochemical quenching (qQ) and non-photochemical quenching (qNP) than did Dongjln. In contrast, zeaxanthin formation was largely influenced by exposure to light rather than to high salinity, with Annapurna having a higher rate of production compared with Dongjin. When both cultivars were exposed to salt stress for 2 d, Annapurna had a much lower rate of photosynthetic oxygen evolution, corresponding to only 46% of the control; the rate for Dongjin was 90% of the control. Salt stress in both cultivars induced the accumulation of two osmoprotectants, glycinebetaine and proline, the rate being higher for the latter. These results indicate that Annapurna is more sensitive than Dongjin to salt stress, in terms of its deterioration in photosynthetic function.

We studied the effects of different co~[et~bral~ns of mercury (0.0 to 100 !~t) o. growth and p~Uc efficiency in rice plants treated for 21 d. In addilJo., we invesl~ated how this metal affected Ihe malondtaidehy~ (MDA) content as well as lhe ~ of five ~ enzymes -superoxJde dimnutase (SOD), ascorbale peroxidase (APX), glutathione reductase (GR), guaiacol pemxidase (POD), and ratalase (CAT). ~c ef@~mcy (F,/Fm) and seedling growth decreased as the cancentrabon of H s was increased in the growth media. Plants also responded to Hg-induced oxidaslbress by charting the levels of their antioxiclat~ enzymes. Enhanced lipid peroxidabon was observed in both leaves and roots that had been exposed to oxldal@e m, with leaves showing higher enzymatic acth~. Both SOD and APX acti@l~s increased in beabnents with up to 50 pM I~, then decreased at higher concentrations. In the leaves, bolh CAT and POD acth~es increased ~radually, with CAT levels decreasing at h~her concentratJon~ In the roots, hm~mver, CAT aclivity remained Ui~-hansed while that of POD increased a bit more than did the control for concen~alJons of up to 10 pM H& At higher Hg levels, beth CAT and POD activities decreased. GR act~ increased in leaves exposed to no more than 0.25 pM Hg, then decreased gradually. In contrast, its activity was greatly inhibited in the roots. Based on these results, we surest that when rice plants are exposed to different concentrations of mercury, their anlJoxidative enzymes become involved in defense mechanisms against the free radicals that are induced by this stress.