The Effects Of Exogenous Polyamines On Some Drought Tolerance Characteristic In Lane Late Navel Orange Saplings

Saplings of Two-year Lane Late navel orange grafted as trifoliate stocks were used in this study. Plants were irrigated with0.5mmol/L Put, Spd or Spm hydroponic solution as well as sprayed onto the leaves, and followed drought stress. This study aimed to explore the effects of exogenous PAs on physiological characteristic and ultrastructure of citrus under drought stress. The main results of the present research are as follows:1. The annual dynamic changes of endogenous PAs content in roots and leaves of Lane Late navel orange saplings. The results showed that Put content in roots changed in Peak shift and reached the maximum430.62nmol/g in August, while the amounts of Spm, Spd and Put in leaves presented the maximum in April at444.88nmol/g,516.42nmol/g and116.91nmol/g respectively, as well as Spd content higher than that of Spm and Put in the whole process. Put was mainly Polyamines in roots whereas Spd and Spm in leaves.2. The effects of exogenous polyamines on endogenous polyamines content in Lane Late navel orange seedlings under drought stress. Under drought stress, Put content in roots and leaves increased by59.84%and300.50%respectively whereas the Spm content in leaves decreased by33.83%on the seventh day. However, after treating with Spm, Spd or Put under drought stress, Put content in roots and leaves was apparently decreased, which reduced by42.21%,38.93%and12.43%respectively in the roots and in leaves by44.61%,25.73%and22.73%on the seventh day, while Spd content in leaves increased by37.20%,39.16%and44.26%respectively under the three treatments and reached the maximum298.54nom/g,302.81nmol/g and313.91nmol/g respectively. As well as the Spm content in leaves increased by74.96%,102.15%,51.92%respectively and reached the most amount at172.20nmol/g on the third day,155.84nmol/g on the seventh day and159.20nmol/g on the fifth day.3. The effects of exogenous polyamines on some drought tolerant characteristics in Lane Late navel orange saplings. Under drought stress, MDA content in leaves and roots obviously increased and the content in leaves higher than that in roots. The treatment of exogenous PAs led to the decreasing of MDA content in leaves and roots in the whole process. The total antioxidant activity in roots and leaves was increased and reached the maximum amount after treated with Spd and Put on the seventh day, especially, the roots total antioxidant activity increased by127.16%and283.95%. Under drought stress, the treatment of three exogenous PAs could slow down the RWC and chlorophyll content decreasing in leaves of Lane Late navel orange, which chlorophyll content increasing by50.99%,33.69%and33.45%respectively compared with the control plants on the fifth day. The soluble sugar content apparently increasing by28.53%,39.12%and18.50%respectively in roots, and by24.97%,31.86%and32.46%in leaves treated with Spm, Spd and Put. The protein content in leaves increasing by15.47%and12.57%respectively at treated with Spd and Put on the seventh day. Under drought stress, the cell ultrastructure was seriously damaged, which the configuration of chloroplast was deformed and dispersed in the cytoplasm and the separation of cytoplasm and cell wall appeared distinctly in mesophyll cells. The obtained results demonstrate that the application of three exogenous PAs could relieve withdrawing extent of Lane Late navel orange, stabilize cell ultrastructure, protect the cell completeness as well as stop the separation cytoplasm from the cell wall and chloroplasts degradation.