Mechanism Of Potassium Enhancing The Proline Accumulation In Tobacco

Proline accumulation in plants under potassium treatment has been reported in several higher plants. however, the way that plants choose to accumulate proline under potassium treatment is still unclear. Study focus on the effect of potassium on proline metabolism under various environment stress is rare. Thus, the present work is to elucidate the mechanism of potassium in promoting the proline accumulation.in tobacco ( Nicotiana tabacum L.) under various environment (without any stress, osmotic stress and salinity stress).Ⅰ. The study on the comparison of potassium nitrate and sodium nitrate without stress showed that :more than 10mmol·L-1potassium nitrate treatment could enhance the proline accumulating significantly. The proline content with 30mmol·L-1potassium nitrate treatment is significantly higher than sodium nitrate treatment. We also found the predominance of the ornithine pathway over the glutamine pathway plays an important role in proline accumulation under potassium nitrate treatment.Ⅱ. The plants were subjected to PEG as an osmotic stress. PEG stress significantly increased the free proline content may due fundamentally to an increase of P5CS activity. The accumulation of proline induced by potassium nitrate application under stress due to an increase of OAT activity.Ⅲ. The plants were subjected to 100 mmol·L-1 NaCl treatment for ten days as a salinity stress. The salt treatment induced proline accumulation, which was due fundamentally to a depression of proline dehydrogenase activity and increase of△1-pyrroline-5-carboxylate synthetase activity. We also found the predominance of the ornithine pathway over the glutamine pathway plays an important role in proline accumulation under potassium nitrate treatment.Ⅳ. In experiment of detached tobacco leaves, the leave discs were treated with distilled water, 5mmol·L-1potassium nitrate, 10mmol·L-1potassium nitrate, 5mmol·L-1sodium nitrate, 10mmol·L-1soduim nitrate for eight hours, before or after exposing to wilting condition, an enhanced accumulation of free proline effected by potassium nitrate was observed. Treatment with sodium nitrate instead of potassium nitrate did not lead to extra prline accumulation.In conclusion, the effect of potassium on proline accumulation was mainly through ornithine pathway, because the potassium activate OAT, which is the key enzyme in proline synthesize pathway-ornithine pathway.