The Gas Exchange,Ultrastructure and Stress Resistance of Lettuce Plants under Short-Term Hypobaric and Hypoxic Conditions

To investigate the possibility of plants cultivation at hypobaria and hypoxia,the gas exchange,ultrastructure and stress resistance of lettuce were conducted under short-term hypobaric and hypoxic conditions. The gas exchange and growth of 25-day old lettuce( Lactuca sativa L. var. Rome) seedlings were tested after 1-h or 24-h equilibration under two levels of total atmospheric pressure( 101 k Pa and 30 k Pa) and three levels of oxygen partial pressure( 21 k Pa,6 k Pa and 2 k Pa). The results showed that the biomass,ratio of root / shoot,water content and mineral contents of lettuce plants were not affected by the changes of total atmospheric pressure and oxygen partial pressure; Under the same total pressure conditions( 101 k Pa or 30 k Pa),hypoxia( 6 k Pa or 2 k Pa) resulted in the increases of photosynthesis rate,soluble sugar and malondialdehyde and the reduction of dark respiration of lettuce leaves. The change of mitochondrion ultrastructure and the decrease of transpiration were found at 2 k Pa oxygen partial pressure; Under the same oxygen partial pressure conditions,photosynthesis rate,the chloroplast ultrastructure,the contents of chlorophyll and carotenoid of lettuce leaves were not affected by short-term hypobaric treatment( 30 k Pa),but the rates of dark respiration and transpiration increased and the contents of soluble sugar and malondialdehyde in lettuce leaves decreased. Lettuce can grow under short-term hypobaric and hypoxic conditions. Short-term hypoxia( 6 k Pa or 2 k Pa) resulted in hypoxic stress and hypobaria( 30 k Pa) enhanced the stress resistance of lettuce.