| Salinity and drought conditions are major factors affecting plant productivity and distribution worldwide. To engineer resistance to dehydration stress in cucumber (Cucumis sativus L.), transgenic cucumber were generated with genes associated with enhanced abiotic stress tolerance: the mannose-6-phosphate reductase (M6PR) gene from celery for mannitol production, and the CBF1/DREB1b and CBF3/DREB1a, abiotic stress-associated transcriptional regulators from Arabidopsis thaliana . T0 transgenic M6PR cucumbers produced detectable mannitol, indicating functionality of the M6PR gene in cucumber. However, mannitol accumulation in the T1 progeny was highly variable making this trait-difficult to work with. Eleven lines of cucumber were produced with the CBF genes, integration and expression was verified in the T0, T1 and T2 generation. Under greenhouse conditions, T 1 and T2 CBF-cucumber plants accumulated elevated levels of proline and soluble sugars, a signature for CBF expression in Arabidopsis, indicating ability of the CBF gene to induce stress related responses in cucumber. Proline and soluble sugars accumulation were highly correlated, suggesting coordinated regulation in the transgenic plants. In the absence of salt or drought stress, the CBF cucumbers showed equivalent growth compared to the nontransgenic controls. In the presence of salt and drought stress, transgenic plants had less reduction in growth. Plant performance and fruit production was evaluated under field conditions. Prior to salinity-stress, transgenic and nontransgenic cucumber lines grew equivalently. CBF -cucumber plants accumulated significantly higher levels of compatible solutes in leaves (proline and soluble sugars) and roots (proline) compared to the nontransgenic controls. Transgenic plants also had elevated levels of K+ and Ca++ ions and a decreased Na +/K+ ratio in root tissues, suggesting a wider range of adaptive responses in the transgenic plants than has been reported previously. In the absence of salinity, CBF lines had less fresh weight than the nontransgenic controls; however, dry weight and fruit yield were equivalent to the nontransgenics. In the presence of salinity stress, CBF-transgenic plants showed significantly less reduction in fresh weight, dry weight, fruit number and fruit weight. These results suggest that expression of the CBF/DREB in cucumber, a species known for sensitivity to salinity and drought conditions, may offer an effective approach to enhance salinity and drought tolerance. |
