Analysis Of Drought Resistance Of Five Citrus Rootstocks Under Pot Culture

In the study, drought resistances of five citrus rootstocks (trifoliate orange. Carrizo citrange, Citrus junos, red tangerine and Goutoucheng) were compared under pot culture. The main results in the present study are as follows:1. Under pot culture, the lethiferous days under drough treatment was the longest in trifoliate orange and in Carrizo citrange, then was Citrus junos and red tangerine or Goutoucheng; during drought stress, the difference of malondialdehyde contents between drought-treating leaves and control leaves was small in trifoliate orange, the difference in Carrizo citrange was significant only at18days after drought treatment and the difference in red tangerine or Goutoucheng was significant since5days after drought treatment; as for hydrogen peroxide(H2O2) content. its content in the leaves of trifoliate orange was slightly higher in drought treatment than that in the control, the difference of H2O2between drought-treating leaves and control leaves was obvious in the leaves of Carrizo citrange only at18days after drought treatment while in the leaves of Citrus junos was obvious since14days after drought treatment and in the leaves of red tangerine and Goutoucheng was obvious since5days after drought treatment. Taken together. the drought resistence of trifoliate orange under pot culture was the strongest. which had the longest lethiferous days under drough treatment. strong ability to control the production of MDA and H2O2, and then was Carrizo citrange and Citrus junos. red tangerine or Goutoucheng had the lowest ability of drought resistence.2. The total antioxidant capacity (T-AOC) and the ratio of L-ascorbic acid to Dehydroascorbate (AsA/DHA) were almost higher under drought treatment than those in control in each rootstock cultivar. Their changing patterns among five rootstocks, implying that the antioxidant capacity has a relationship with drought resistence but was not the main reason of the different drought resistence of the five rootstocks.3. Activities of enzymes involving in Ascorbate-Glutathione (AsA-GSH) cycle were analyzed in trifoliate orange (the strongest drought resistence). Citrus junos(the moderate drought resistence) and red tangerine(the weakest drought resistence). Results indicated that enzyme activities of monodehydroascorbate reductase (MDHAR) dehydroascorbate reductase(DHAR) and glutathione reductase (GR) were increased immediately by drought treatment and were obviously higher than those in control among three rootstock cultivars. Changes in enzyme activities of ascorbate peroxidase (APX) varied in the three cultivars. Namely. APX activities in the leaves of trifoliate orange and Citrus junos were increased immediately by drought treatment and were always obviously higher than those in the control during drought treatment. In red tangerine. APX activity was slightly increased, and then decreased at9days after drought treatment and was obviously lower than that in control at14days after drought treatment. APX catalyzes H2O2to produce water H2O in plant cell. Hence, trifoliate orange had the strongest drought resistence under pot culture may be related with the higher activities of APX. which provides the strong ability to control the H2O2content, then to relieve the damage caused by H2O2.4. Gene expression analysis indicated that expression levels of genes of MDHAR, DHAR and GR were induced by drought treatment and showed some difference among three cultivars. However, the difference did not related with the drought resistence of these rootstock cultivars. As for APX genes, their changing patterns of gene expression were similar with the enzyme activity during drought treatment. Gene expression of APX6and tAPX in the leaves of trifoliate orange and Citrus junos were induced by drought treatment and were always obviously higher than those in the control during drought treatment:In red tangerine. APX activity was slightly increased, and was obviously higher than that in thecontrol at9days after drought treatment, and then decreased to the same level as in the control.