Effects of Drought Stress on Seed Germination and Seedling Physiological Characteristics of Rhododendron latoucheae

In order to explore the drought tolerance of Rhododendron latoucheae in seed germination and seedling growth stage,we studied the effects of drought stress on seed germination,growth,cell membrane permeability,malondialdehyde(MDA)content,the organic osmoregulation substances and antioxidant enzyme activities by choosing dry seeds and seedlings with 90 dage and using different concentrations of polyethylene glycol(PEG-6000)simulated drought stress.The regression analyses were done between seed germination,early seedling growth and PEG stress.The results showed that:(1)the initial germination time of R.latoucheae seeds was delayed with the increasing of drought stress degree in 5%-25% PEG range,and the germination duration was prolonged.The seed germination rate,germination potential,germination index,vigor index and early seedling growth were all significantly reduced.The seed could notgerminate absolutely at severe drought stress(25% PEG).(2)The changes of seed germination rate,germination potential,germination index,vigor index and early seedling growth were showed very significant negative correlation with the degree of drought stress.The regression equation between seed germination,early seedling growth and PEG stress showed that the half lethal PEG drought stress concentration was15.68%,while the semi dwarfing PEG drought stress concentration was 15.37%.(3)With the increase of PEG concentration,SOD activity of R.latoucheae seedling leaves increased firstly and then decreased,but were significantly higher in all the stress treatments than that of CK(0% PEG).Cell membrane permeability,MDA content,proline content,soluble sugar content,POD and CAT activities increased significantly in moderate(15%-20% PEG)and severe drought stress,and the changes of these indexes were showed very significantly positive correlation with the degree of drought stress.The research found that seed germination and seedling growth of R.latoucheae were significantly inhibited by drought stress,and cell membrane was also damaged in different degrees.Thus it could be seen that R.latoucheaeincreased contents of the osmoregulation substances and antioxidant enzyme activities in vivo to adapt to drought stress environment at the same time,making the inhibition and damage degree to the minimum.