克隆整合提高淹水胁迫下狗牙根根部的活性氧清除能力

虽然国内外已开展大量关于克隆整合影响植物抗逆生理的研究,但迄今未见克隆整合是否会影响逆境下不同分株清除活性氧过程的报道。以河岸带适生克隆植物狗牙根(Cynodon dactylon)为例,研究克隆植物的抗氧化生理响应,检测了狗牙根在先端淹水/不淹水、先端与基端匍匐茎连接/切断两个因素的交互作用下的根部主要抗氧化酶:超氧化岐化酶(Superoxide dismutase, SOD)、抗坏血酸过氧化物酶(Ascorbate peroxidase, APX)、过氧化氢酶(Catalase, CAT)的活力以及生物量的变化。结果显示,淹水环境中狗牙根先端的生物量和根部SOD酶活力在匍匐茎连接处理下显著高于切断处理组,同一处理的生物量以及根部APX、CAT酶活力总体上表现出不同程度的提高趋势;与受淹先端连接的基端分株根部抗氧化酶活力均低于切断处理组,且SOD和CAT受连接处理影响显著;淹水和切断处理显著降低先端分株的生物量,但对基端和克隆片段影响不明显。这表明淹水胁迫下克隆整合提高了其根部活性氧清除能力,显著改善了先端分株的表现。

Clonal integration enhances the ability to scavenge reactive oxygen species in root of Cynodon dactylon subjected to submergence

Clonal integration, allowing resource to be shared between ramets, is a unique biological characteristic for clonal plants. Ramets of stoloniferous and rhizomatous species internally translocate resources from sites of high supply to sites of high demand via physical connections among them, resulting in enhanced performance of ramets and/or ramet system under environmental stresses. On the other hand, environmental stresses always induce accumulation of reactive oxygen species (ROS), which attack membrane integration, deactivate protein function and subsequently interrupt normal metabolism process. Although there is a large body of knowledge on how clonal integration improves the performance of clonal plants, its effect on the activity of enzymes responsible for scavenging ROS, remains unknown. Here we investigated the influence of clonal integration on ROS of Cynodon dactylon,a stoloniferous clonal herb commonly found in riparian areas of reservoirs, subjected to waterlogging stress. Clonal fragments with 4 ramets were placed in pots divided into 2 chambers. The 2 apical (relatively younger) ramets of each fragment were submerged in water at depth of 0(control) or 15 cm, with the stolons connecting to the basal (relatively older) ramets under normal condition either severed (preventing clonal integration) or not (allowing integration). The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT) from root tissue of apical and basal ramets of C. dactylon were measured. Meanwhile, the biomass of apical and basal ramets after 20 days' treatments was also measured to investigate whether clonal integration executed "enhancing effect" on performance of C. dactylon. Compared to 41.4% reduction of apical biomass under connection and waterlogging treatment, severing significantly decreased apical biomass by 58.8% under waterlogging stress, suggesting that clonal integration could improved the performance of apical ramets of C. dactylon. However, such effect was not found in terms of basal biomass. Under waterlogging stress, physical connection greatly increased root SOD activity of apical ramets up to control level, while disconnection significantly decreased it to 41.7% of the value of the control treatment. Furthermore, disconnection combined with waterlogging treatment also drops root APX and CAT activity of apical ramets to some extents. On the other hand for basal ramets, physical connection induced significant reduction of root SOD and CAT activities to 35.8% and 51.3% of the control level under waterlogging stress. These results illuminated that clonal integration could ameliorate the balance between regeneration and scavenging of reactive oxygen species under waterlogging stress imposed to apical ramets, which probably was one of the key biochemical processes responsible for the enhanced performance of clone plants. To our knowledge, this is the first report that clonal integration affects the activities of SOD, APX, and CAT, the three key enzymes responsible for scavenging reactive oxygen species which would commonly accumulate and subsequently interrupt plants' normal metabolism under environmental stresses. Therefore, we suggested that clonal integration could not only adjust anatomic/structural/physiological processes, but also ameliorate the balance between regeneration and scavenging of reactive oxygen species, to improve the performance of stressed ramets. Furthermore, we also thought that resource transport between apical and basal ramets was the main mechanism attributed to the variation of ROS scavenging enzyme activity.