| This study use own-root mulberry and grafted mulberry (stock:Tailai mulberry; Scion:Long mulberry) as materials, under the natural conditions, cold hardening, low temperature stress and so on, measured photosynthetic parameters, fluorescence,antioxidant activity and other indicators, research own-root mulberry and grafted mulberry photosynthetic system response and adaptability under low temperature environment, all the main results as follows:(1) Under natural conditions, grafting mulberry and own-root mulberry light response curve and the carbon dioxide response curves showed that grafted mulberry and own-root mulberry net photosynthetic rate showed an upward trend, all grafted mulberry leaf were higher than the own-root mulberry obvious. grafted mulberry the efficient of using light energy than own-root mulberry, the ability of photosynthetic institutions and the efficiency of organic synthesis have higher than own-root mulberry. Stomatal conductance (Gs) of grafted mulberry is higher than own-root mulberry in each leaves, photosynthesis and transpiration in the physiological activities are strong, the metabolism is better than own-root mulberry.(2) Under natural conditions, in different leaf positions of the same branch and different position of leaves,grafted mulberry is higher than own-root mulberry on the actual photochemical efficiency of PSⅡ, electron transport rate (ETR), the photochemical quenching coefficient (qP) and non photochemical quenching (NPQ) is lower than grafted mulberry. It is show that the open ratio of PSⅡreaction centers of grafted mulberry and photochemical efficiency and electron transport rate, synthesis of organic compounds absorb light energy for photosynthesis capacity than own-root mulberry, and composing a large number of organic synthesis easily.(3) Cold temperature damage is a common problem for mulberry production in Northeast China. Many attempts have been made to improve cold tolerance in mulberry plants, and one of the methods tested is cold hardening. The objectives of this research in this paper are to investigate cold tolerance in mulberry seedlings induced by cold hardening to identify mechanisms of chilling tolerance. The seedlings of mulberry variety 'Qiuyu' were exposed to 12℃(cold hardened) or 25℃(unhardened) for 3 d under 220～250μmol·m-2·s-1 PDF. All seedlings were then transported to cold stress at 3℃for 3 d and allowed to recover at 25℃for 2 d. The results showed that resistance to cold stress in leaves of mulberry seedlings was induced by cold hardening at 12℃for 3 d. Net photosynthetic rate (Pn), stomatal conductance (Gs) and the maximum photochemical efficiency of photosystemⅡ(Fv/Fm) in cold hardened leaves of mulberry seedlings under cold stress at 3℃for 3 d were higher than that of unhardened leaves, and cold hardened leaves of mulberry seedlings also recovered faster from cold stress than unhardened leaves. Proline contents and soluble sugar contents in leaves of mulberry seedlings during cold hardening, and proline contents and soluble sugar contents as cell osmolytes in cold hardened leaves of mulberry seedlings during cold stress and recovery were higher significantly than that of unhardened leaves. Malondialdehyde (MDA) contents in cold hardened leaves of mulberry seedlings during cold stress and recovery were lower significantly than that of unhardened leaves. Ascorbate peroxidase (APX, EC1.11.1.11) activities in cold hardened leaves of mulberry seedlings during cold hardening, cold stress and recovery were higher significantly than that of unhardened leaves. It concluded that osmolytes and APX activities in leaves of cold hardened leaves of mulberry seedlings played important role in cold tolerance induced by cold hardening.(4) Using the own-root mulberry and grafts mulberry as the test material,the propose was to study on the effects of low temperature stress on chlorophyll fluorescence parameters of mulberry.The results showed that under the low temperature stress,the chlorophyll fluorescence in own-root mulberry and grafts mulberry showed obviously change. Both of them actual photochemical efficiency of PSⅡ(ΦPSⅡ),the electron transport rate (ETR),the diurnal changes of the maximum PSⅡphotochemical efficiency(Fv/Fm) and the photochemical quenching coefficient (qP) were decrease intensity, Minimal fluores-cence (Fo) and non photochemical quenching (NPQ) was risen, while the rising extent of NPQ in own-root mulberry was higher than that in grafts mulberry,It is shown that the ability of PSⅡresisting low temperature stress in grafts mulberry than that in own-root mulberry. Low temperature stress not only caused the change of photosynthetic structure in mulberry directly, but also affect the transformation of photosynthetic electron.The descend content of SOD and POD in grafts mulberry smaller than own-root mulberry,and the ascend content of MDA and oluble sugar contents in grafts mulberry higher than own-root mulberry, it is shown that grafts mulberry have better ability of cold tolerance. |
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