摘要
为探究淹渍胁迫后枳砧温州蜜柑(Citrus unshiu Marc.)植株的形态特征变化及其生理响应机制,以枳砧‘市文’温州蜜柑成年树为试材,进行盆栽土壤淹水胁迫处理,将植株根部分别淹渍处理2、5、10、15、20 d,以正常灌溉为对照(CK),观察其形态学及根系解剖结构特征的变化,并测定叶片的光合参数、叶片和根系的渗透调节物质、无氧呼吸酶活性、丙二醛含量及树体矿质营养元素等指标。结果显示:淹渍5 d时,根系开始出现异味且韧皮部细胞饱满膨胀;淹渍10 d时,新老叶片已呈现不同程度的黄化,根系开始腐烂、变色,淹渍20 d左右,树体干枯死亡。与对照相比,淹渍胁迫处理早期(5 d内),根系乙醇脱氢酶活性显著升高,随着淹渍胁迫时间的延长,根系中游离脯氨酸、可溶性糖和可溶性蛋白含量显著降低并维持在较低水平,丙二醛含量仅在淹渍10 d时显著高于对照。相同处理条件下,叶片中的叶绿素含量随淹渍时长持续下降,淹渍处理10 d时叶片的胞间CO2浓度显著升高,净光合速率、气孔导度和蒸腾速率显著下降。叶片中游离脯氨酸、可溶性蛋白、丙二醛和相对电导率自淹渍处理10~20 d均显著高于同期对照。淹渍胁迫5 d和20 d时,茎和叶片多数矿质营养积累未发生变化,根系中的P、K、Ca、Mg含量与对照相比显著减少。结果表明,枳砧温州蜜柑不同组织对淹渍胁迫后的生理响应存在明显差异,叶片相对电导率和根系乙醇脱氢酶对淹渍胁迫的响应敏感;长期淹渍胁迫影响植株的光合性能、渗透调节物质含量及乙醇脱氢酶活性的变化,使叶片和根系出现明显可见的胁迫症状,导致植株生长缓慢,甚至死亡。
柑橘是我国南方地区产量最大和分布最广的亚热带果树。由于多数柑橘产区春夏季节雨季较长,降雨量大,橘园常出现雨季积水浸根,甚至洪涝淹树等不同程度的淹渍胁迫。因此,了解柑橘淹渍胁迫后的树体状况及淹渍响应生理机制对于正确评估柑橘淹渍灾害影响及灾后恢复性生产十分重要。
淹渍胁迫对植株的影响主要表现为植株形态和生理改变,引起植株根系腐烂,进而造成植株无氧呼吸加
我国柑橘产区春夏季节连续阴雨易导致橘园淹渍频繁发生,淹渍胁迫对柑橘坐果及果实发育、产量品质形成、花芽分化均有较大影响,是当前柑橘生产亟需解决的问题之
试验于2019年5-6月在湖南农业大学温室大棚(28°17'99″ N,113°07'71″ E)内进行。以栽植于黑色塑料桶(直径40 cm,高34 cm)中的9年生枳砧‘市文’温州蜜柑(Citrus unshiu Marc.‘Ichifumi Wase’)为材料,栽培基质为V锯木屑∶V河沙∶V草炭=2∶1∶0.5。根据该地区春夏之交持续降雨规律性明显的特点,试验于5月16日开始,淹渍处理(waterlogging stress,WL)采用双套盆法,在打孔的桶外再套1个无孔的黑色塑料桶,控制淹水水面超过土壤表面1 cm。淹渍历时设2、5、10、15、20 d共5个处理;同期设置的对照(CK)进行正常水分管理,使基质相对含水量维持在(70±10)%。使用便携式土壤水分监测仪监测水分含量,确保相对含水量稳定。以上每个处理3次重复。大棚温湿度情况使用温湿度数据记录仪记录(

图1 试验期间大棚温湿度
Fig.1 Temperature and relative humidity in the greenhouse during the present experiment
TDR便携式土壤水分监测仪,美国Spectrum technologies;DT-171温湿度数据记录仪,中国CEM;Pannoramic MIDI 数字切片扫描仪,匈牙利3DHISTECH;LI-6400携式光合仪,美国LI-COR Inc;Multiskan Sky全波长酶标仪,美国赛默飞;DDS-11A电导率仪,上海雷磁;KDN-103F自动定氮仪,上海纤检;Thermo-902超低温冰箱,美国赛默飞。
每个处理达到设定淹渍时间后,对叶片和根系拍照并观察其形态学变化;将试验材料整株拔出,先用自来水冲去土壤和杂质,再用蒸馏水冲洗干净,然后用滤纸和吸水纸擦净材料上的水分,选取根尖粗度及成熟度相对一致的根段,放入乙醇-醋酸-福尔马林混合固定液(FAA固定液)中保存,采用石蜡切片方法观察根系解剖结
分别取CK和淹水处理2、5、10、15、20 d的植株细根和秋梢叶,其中叶绿素和相对电导率测定用新鲜叶片,其余均剪碎混匀、液氮速冻后放入-80 ℃超低温冰箱保存,矿质元素测定将试验材料的根、茎、叶分开,放入105 ℃烘箱杀青30 min后,烘箱温度调至70 ℃烘干至恒质量,样品粉碎后过孔径0.15 mm筛待测,所有测定指标均设3次重复。
叶绿素含量采用乙醇浸提
脯氨酸含量采用磺基水杨酸提取,酸性茚三酮法测定;可溶性蛋白含量采用BCA法测
春末夏初,大棚内日均温度25 ℃左右,相对湿度73%左右,温州蜜柑外观形态和根系解剖结构受淹渍胁迫的影响随淹渍时间的延长而加剧。由

图2 淹渍胁迫后枳砧温州蜜柑地上部(A)和根系(B)形态变化
Fig.2 Morphological changes of the shoots(A) and root(B) of satsuma mandarin with trifoliate orange rootstocks after waterlogging stress
CK:对照;WL:淹渍处理。下同。CK:Control;WL:Waterlogging treatment.The same as follows.

图3 淹渍胁迫下枳砧温州蜜柑根系解剖结构变化
Fig.3 Changes on root anatomical structure of trifoliate orange grafted with satsuma mandarin after waterlogging stress
A和C分别代表CK在处理5 d时根系横截面;B和D分别代表淹渍处理5 d时根系横截面;E和G分别代表CK在处理20 d时根系横截面;F和H分别代表淹渍20 d时根系横截面。A and C respectively represents roots cross section of CK 5 d,B and D respectively represents roots cross section of flooded 5 d,E and G respectively represents roots cross section of CK 20 d,F and H respectively represents roots cross section of flooded 20 d.
淹渍胁迫导致温州蜜柑叶片中叶绿素及类胡萝卜素的含量显著降低。其中,温州蜜柑淹渍处理叶片中的叶绿素含量从第10 天始显著降低,且随胁迫时间的延长持续下降。温州蜜柑叶片中叶绿素a(chlorophyll a,Chl a)、叶绿素b(chlorophyll b,Chl b)和类胡萝卜素(carotenoid,Car)的含量在淹渍胁迫5~10 d变化最为剧烈,特别是淹渍10 d时各色素组分分别较同期CK显著降低57.14%、47.73%、21.74%,且随淹渍时间的延长而持续下降,淹渍20 d降至最低值,此时温州蜜柑叶片中Chl a、Chl b、Car的含量分别较同期CK降低86.07%、78.43%、86.36%,Chl总含量仅是CK的11.97%(

图4 淹渍胁迫下枳砧温州蜜柑叶片叶绿素变化
Fig.4 Changes of chlorophyll content of satsuma mandarin leaves with trifoliate orange rootstocks after waterlogging stress
不同字母表示在α=0.05水平差异显著。下同。Different letters indicate significant differences at α=0.05 level.The same as below.
由
注: * 表示同一指标处理间在α=0.05水平差异显著。Note:* indicates significant difference at α=0.05 level between treatments.
温州蜜柑根系中的渗透调节物质从淹渍2 d开始持续下降,叶片中的渗透调节物质在淹渍10 d后升高。淹渍树体根系中的脯氨酸(proline,Pro)含量随淹渍时间的延长呈下降趋势,淹渍20 d时较CK显著下降91.44%(

图5 淹渍胁迫下枳砧温州蜜柑根系(A、C、E、G)和叶片(B、D、F、H、I)的渗透调节物质和膜脂过氧化程度变化
Fig.5 Changes on osmotic regulation substance and membrane lipid peroxidation in satsuma mandarin with trifoliate orange rootstocks roots(A,C,E,G) and leaves(B,D,F,H,I) after waterlogging stress
淹渍逆境下温州蜜柑根/叶的丙二醛(malondialdehyde,MDA)及相对电导率(relative electrical conductivity,EL)均呈现动态变化。温州蜜柑淹渍处理后,叶片MDA含量表现为随处理时间延长呈逐渐增加的趋势(
淹渍胁迫下,温州蜜柑根系活力明显降低,无氧呼吸酶活性在淹渍早期急剧升高而后随淹渍时间的延长呈下降趋势。脱氢酶(dehydrogenase ,DHA)活性是反映根系活力的重要指标。淹渍后温州蜜柑根系的DHA活性总体呈下降趋势,且从淹渍10 d开始显著低于CK,直至淹渍处理结束(

图6 淹渍胁迫下枳砧温州蜜柑根系活力DHA(A)和乙醇脱氢酶ADH(B)活性变化
Fig.6 Changes of trifoliate orange grafted with satsuma mandarin root DHA(A) and anaerobic respiration enzyme activity(B) after waterlogging stress
淹渍胁迫后,叶片与根系的抗逆理化指标多数呈极显著负相关。根系Pro和SP与叶片Pro、SP、SS、MDA和EL呈负相关,根系的SS与叶片的Pro、MDA和EL也呈负相关;根系的MDA和叶片Pro呈极显著正相关(r=0.669)(
注: **表示相关系数达到极显著水平(0.01)。Note:** represent significantly different 0.01 level.
淹渍胁迫导致枳砧温州蜜柑根系中P、K、Ca、Mg含量减少,茎、叶中的各矿质元素含量无显著变化。根系中P含量在淹渍5 d和20 d时均显著降低,20 d时较CK降低40%(

图7 淹渍胁迫对枳砧温州蜜柑树体内N(A、B、C)、P(D、E、F)、K(G、H、I)含量的影响
Fig.7 Effects of flooding stress on contents of N(A,B,C),P(D,E,F) and K(G,H,I) in satsuma mandarin trees with trifoliate orange rootstocks

图8 淹渍胁迫对枳砧温州蜜柑树体Ca(A、B、C)、Mg(D、E、F)、Fe(G、H、I)、Zn(J、K、L)含量的影响
Fig.8 Effects of flooding stress on contents of Ca(A,B,C),Mg(D,E,F),Fe(G,H,I) and Zn(J,K,L) in satsuma mandarin trees with trifoliate orange rootstocks
淹渍条件下植物气体扩散受阻、叶绿素降解、光合速率下降、产生无氧呼吸,干扰植物正常的生理代谢及生长发育,为了适应淹渍条件,保障正常的生理代谢功能,植株地上部和地下部形态通常会发生改
已有研究表明,水分胁迫下,果树叶片的叶绿素降解加
植物在淹渍逆境中启动的细胞膜脂过氧化系统可导致生物膜严重损
根系是植物从土壤中吸收、运输水分及养分的重要器官,其活力的高低是衡量植物抗逆性的重要指标之一。随着淹水胁迫时间的延长,猕猴桃的根系活力逐渐下降,其下降程度受基因型的影
ADH活性及叶片EL作为耐涝性的重要生理指标,已广泛应用于观赏植
植物主要依靠根系吸收矿质元素,淹渍胁迫直接对根系造成伤害,减少根系对矿质元素的吸收量。研究表明,玉
本研究结果表明:枳砧温州蜜柑的地上部和地下部组织响应淹渍胁迫的敏感程度及响应存在显著差异。根系是直接受到淹渍胁迫伤害的器官,较叶片更早响应淹渍胁迫,根系ADH活性变化与根系受伤害程度紧密相关,叶片EL与受淹渍胁迫程度密切相关。
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