Chilling of shoot cultures from Oryza sativa L. cv. Taipei 309, to 4 ~ leads to conditions of oxidative stress. Tissue H202 was observed to increase more than fourfold by 8 d of chilling, and levels of reduced glutathione, which normally rise in growing shoot cultures at 25 ~ were considerably repressed in chilled cultures. Whilst the activity of ascorbate peroxidase in chilled shoots remained similar to the activities in control cultures at 25 ~ the most notable effects of chilling to 4 ~ were the very significant loss of catalase and glutathione reductase activity. Although prior exposure of shoot cultures to abscisic acid (ABA) at 25 ~ increased levels of catalase activity, such increased levels were not sustained when the pre-treated cultures were placed at 4 ~ Moreover such pre-treatment with ABA did not increase the subsequent ability of shoot cultures to grow at 4 ~

Oxidative injury and antioxidant responses were investigated in two banana genotypes (Musa AAA 'Berangan' and Musa AA 'Mas') subjected to 40 % PEG-induced water stress. PEG treatment resulted in oxidative injury, as expressed in increased lipid peroxidation and reduced membrane stability index, in both cultivars; however, greater oxidative injury was detected in 'Mas'. Under PEG treatment, catalase activity and glutathione reductase activity were enhanced in both cultivars, but were higher in 'Mas'. Ascorbate peroxidase activity was enhanced in 'Berangan' under water stress, but was unaffected in 'Mas'. Meanwhile, superoxide dismutase activity was inhibited in both cultivars under water stress, but higher activity was detected in 'Berangan'. Higher ascorbate peroxidase and superoxide dismutase activities were associated with greater protection against water stress-induced oxidative injury.Additional key words: oxidative stress, ascorbate peroxidase, superoxide dismutase, glutathione reductase, catalase, lipid peroxidation.

No abstract

Eurycoma longifolia Jack is well known among the communities in Southeast Asia because of its aphrodisiac properties and its effectiveness as the cytotoxic, anti-malarial, anti-ulcer, anti-tumor promoting and anti-parasitic agent. Micropropagation through direct plant regeneration from in vivo shoot tip explants was carried out. The highest regeneration percentage (90%) and multiple shoots formation were obtained with the basal Murashige and Skoog (MS) medium supplemented with 5.0 mg l Ϫ1 kinetin. Roots were induced after 14 days of culture in the basal MS medium supplemented with 0.5 mg l Ϫ1 of indole-3-butyric acid. Plantlets regenerated from shoot tip explants survived well with no morphological differences from parent plants after two months of transplantation to soil.

exposed in order to assess t h e consequences of oxidative stress tolerance cannot reproduce those that will be experienced in field conditions. Only when plants with higher GR levels a n d increased glutathione synthesis capacity are grown in field trials will it be possible to make a full assessment of the benefits of engineering plants with altered glutathione metabolism.