Abstract:

This research investigated the responses of leaf senescence and the active oxygen scavenging system following water deficit stress in oats， in order to provide a theoretical framework for evaluation of drought-resistance of oat varieties used on the Qinghai-Tibetan Plateau. A popular local Qinghai oat variety， Qingyan No.1， was used in the experiment. Water deficit stress was simulated with PEG-6000 at two concentrations （P₁₀ and P₂₀）_{and a nil-PEG （CK） treatment was also included. These treatments were applied to plants for 4， 7， or 10 days. The effects of drought stress on the photosynthesis parameters， chlorophyll content， carotenoid content， superoxide anion content， hydrogen peroxide content， antioxidant enzyme activities and non-enzymatic antioxidants were studied. It was found that： 1） With increase in drought stress， the chlorophyll （Chl） content of oat seedlings decreased significantly； superoxide anion content （O2^-） and hydrogen peroxide （H2O2） contents increased significantly； net photosynthetic rate （Pn）， transpiration rate （Tr）， intercellular CO2 concentration （Ci）， stomatal conductance （Gs）， maximum photochemical efficiency （Fv/Fm）， and actual photochemical efficiency （ΦpsII） decreased significantly； and chlorophyll initial fluorescence （Fo） and the non-photochemical quenching coefficient （NPQ） increased significantly. Water deficit stress initially increased plant water use efficiency， but this effect was short-lived and stomatal closure and damage to light reaction centers were the main reasons for the weakening of photosynthetic performance under water deficit. 2） With increase in PEG concentration， or duration of simulated water deficit stress， the activities superoxide dismutase （SOD）， and related enzymes dehydroascorbate reductase （DHAR）， glutathione reductase （GR）， and ascorbic acid peroxidase （APX） increased initially and then decreased， while glutathione peroxidase activity（GPX） continued increasing. However， levels of non-enzymatic antioxidants of oats were significantly higher under drought stress than in control plants. It was concluded that under mild drought stress or in early drought stress， ‘Qingyan No.1’oats remove reactive oxygen species and toxic substances mainly through enzyme antioxidants， while under severe stress， they are removed mainly through non-enzyme antioxidants.}

Key words: drought stress, oat, seedlings