淹水胁迫对‘纽荷尔脐橙’/枳幼苗形态及生理特性的影响

Effect of soil flooding stress on morphological and physiological characteristics of young plants of ’Newhall Navel Orange’/Poncirus trifoliata(L.) Raf.

【目的】研究淹水胁迫后脐橙植株形态学特征变化并揭示脐橙响应淹水胁迫的生理学机制。【方法】以枳砧‘纽荷尔脐橙’幼苗为材料,进行盆栽土壤淹水胁迫处理,观察其形态学及解剖结构特征变化,并测定叶片和根系活性氧物质变化、抗氧化酶活性、丙二醛含量、可溶性蛋白及可溶性糖等物质变化。【结果】土壤淹水处理20 d内,脐橙幼苗叶片外观形态及微观结构均无明显变化,根系出现裂生型气腔;长期(45 d)淹水后,脐橙幼苗叶片叶脉(上部叶主脉、侧脉以及细脉,下部叶主脉)明显变黄,而脉间相对保持绿色,根系生长受到抑制并伴有发黑现象。淹水胁迫(10 d内)诱导叶片和根系活性氧物质含量增加,随后抗氧化酶系统启动,POD和CAT活性在淹水后15 d均显著高于对照。长期(45 d)淹水胁迫后,叶片抗氧化酶仍维持较高活性,而根系酶活性则显著降低。另外,相同处理条件下,脐橙幼苗根系POD活性远高于叶片,而CAT活性远低于叶片。长期淹水后,叶片和根系的可溶性糖含量均显著高于对照,而可溶性蛋白含量均显著低于对照。【结论】‘纽荷尔脐橙’幼苗不同器官响应淹水胁迫的敏感程度及调控机制存在明显差异,各器官会通过形态结构变化、抗氧化酶活性变化以及渗透调节物质含量变化等协同调控;长期淹水则影响体内代谢过程,诱导叶片和根系出现明显的可见症状,抑制脐橙的生长发育。

【Objective】Soil flooding constitutes a seasonal factor that negatively affects plant performance and crop yield.‘Newhall Navel Orange’is the leading citrus cultivar in southern Jiangxi province.It often encounters the waterlogging stress caused by seasonal rainfall during its growth and development period.The present study aims to clarify the changes in morphological characteristics of navel orange plants after flooding treatment,and to reveal the physiological mechanism of navel orange/Poncirus trifoliata(L.)Raf.in response to flooding stress.It is of great significance for timely taking corresponding measures to alleviate the adverse effects of soil flooding stress on the growth,development,fruit yield and quality of navel orange.【Methods】Young‘Newhall Navel Orange’/Poncirus trifoliata(L.)Raf.plants with only 1 shoot were transplanted into plastic pots(24 cm diameter×26 cm height).These pots contained 9.0 kg of soil obtained from a commercial citrus orchard.Waterlogging stress treatments were carried out 3 months after transplanting.Soil flooding was imposed by placing the treated pot into a larger plastic bucket(35 cm diameter×33 cm height)?lled with tap water to 3 cm above the bottoms of the pots.The non-waterlogged pots were well-watered(60%to 80%of field moisture capacity)throughout the experiment.Navel orange plants were sampled after 5,10,15,20 and 45 days of the treatments,respectively.The plants were then separated into upper leaf,lower leaf and fine roots.The potted plants were used to compare the effects of waterlogging on the changes of morphology and anatomical structure,reactive oxygen metabolism,antioxidant enzyme activities superoxide dismutase(EC 1.15.1.1),peroxidase(EC 1.11.1.7),catalase(EC 1.11.1.6),oxidative damage in terms of malonaldehyde(MDA)concentration,soluble protein and soluble sugar under full flooding condition.【Results】The control plants did not show any symptoms throughout the experimental period.Within 20 days of soil flooding treatment,there were no obvious visible symptoms in above-ground plant parts,and the leaf microstructure did not change significantly.The roots showed a schizog-enous air cavity.After long-term(45 days)flooding,the main veins,lateral veins and fine veins of the upper leaves in navel orange plants had obvious yellowing symptoms,while the inter-veins remained relatively green;the lower leaf veinsd,the main veins turned yellow,the lateral veins turned slightly yellow,and the interveins remained green;root growth was inhibited and accompanied with blackening.Compared with the non-waterlogging treatment,waterlogging treatment did not affect the relative chlorophyll content in the lower leaves within 20 d treatment,but signi?cantly increased the relative chlorophyll content in the upper leaves on the 5 th day of flooding.Long-term flooding signi?cantly decreased the relative chlorophyll content both in the upper and lower leaves.There was no significant difference in MDA content of upper leaves between the flooded plants and the control within 20 days of treatment.On the 5 th day of flooding treatment,the MDA content in the lower leaves was even lower than that of the control.With the prolongation of flooding time,the MDA content increased but remained not significantly different from the control.The content of active oxygen species in leaves and roots was increased by waterlogging stress,and then the antioxidant enzyme system started.The rootO 2-·concentration increased significantly accompanying with the root MDA content on the 10 th day of flooding treatment,indicating that the root cells were damaged and the membrane lipid peroxidation increased.The activity of POD and CAT was significantly higher than that of the control on the 15 th day of flooding.After long-term flooding stress,the upper-and lower-leaf antioxidant enzymes maintained high activity and the root enzyme activity decreased significantly.In addition,the POD activity in the roots of navel orange plants was much higher than that in the leaves,and the CAT activity was much lower than that in the leaves.The upper leaves and roots of navel orange plants accumulated more soluble sugar in the early flooding period(5 days),while the lower leaves were less affected by flooding stress.Within 20 days of flooding stress,there were significant organ differences in the response of soluble sugar and soluble protein to waterlogging stress in upper leaves,lower leaves and roots.On the 5 th day of flooding treatment,the soluble protein content of the upper leaves increased significantly,while the soluble protein content of roots decreased significantly.On the 10 th and 15 th days following,the soluble protein content of the lower leaves was significantly lower than that of the control and the roots were significantly higher than that of the control in the soluble protein content.After long-term(45 days)flooding,the soluble sugar content of leaves and roots was significantly higher than that of the control,while the soluble protein content was significantly lower than that of the control.【Conclusion】With a period of flooding stress to‘Newhall Navel Orange’/Poncirus trifoliata(L.)Raf navel orange plants,the sensitivity and regulation mechanism of different organs in response to flooding stress were significantly different.Each organ would be co-regulated by changes in morphological structure,antioxidant enzyme activities and changes in osmotic adjustment substance content.However,long-term flooding stress would affected the metabolic process within the cell,and would induce obvious visible symptoms in the leaves and the roots,and inhibit the growth and development of the‘Newhall Navel Orange’/Poncirus trifoliata(L.)Raf plants.