The Effects Of Pb Stress On The Cell Structure And Nuclear DNA In Isoetes Sinensis

At present, the economy of China is developing rapidly while the environment isdeteriorating, in which Pb pollution has become one of the serious harm in five heavymetals to human health and the environment of because of its wide distribution, severeinfluence and stealthiness and thereby it has been highly valued.Isoetes (Isoetes sinensis) is the first species of Isoete found in China, which has ahigh research value due to its ancient origins and independent route of the evolution.Human activities and tourism development have caused the huge damage on theiraquatic habitat, which leading to its distribution range and population are decreasing.Thus, it has been listed as rare and endangered plant at national level. Research responseof Isoetes which called "plant living fossil " to heavy metal stress not only helps tounderstand the adaptation of ancient plant to the environment, but also offers a new wayfor phytoremediation of heavy metal pollution.Here we used the Isoetes as the test material and performed with2000mg/L ofPb(NO3)2solution stress treatment. Subsequently, inductively coupled plasma massspectrometry was used to measured the content of Pb and the transmission electronmicroscopy was used to observe the changes of cell ultrastructure. Moreover, we usedthe agarose gel electrophoresis to analyze the DNAdamage. The results are as follows.(1) Pb2+can enter the body through the root system, and thereby transport up totubers and leaves; it can also be absorbed by the leaves through transporting up or down,in which transport only down to the tubers.(2) Isoetes leaves can absorb and enrich the Pb2+. It has a strong anti-stresscapability to Pb. Cultured Isoetes in2000mg/L of Pb solution for5weeks resulted in thePb content in leaves which contact with processing solution directly can be up to95906.67±8672.03mg/Kg (dry weight), while the whole plant still maintained well.(3) DNA damage of each organ in Isoetes assumed decreased content but notdegradation of DNA in that it may occur cross linking. The damages of DNA in variousorgans of Isoetes were also different. The damages to the root system were lower than the damages to the upper and lower leaves.(4) Root cell ultrastructure under Pb stress assumed multiple manifestations suchas partly cracked nucleolus, swelled mitochondrial cristae, blurred membrane structureand schizolytic vacuole. The leaves contact with processing solution indirectly, of whichcell ultrastructure revealed swelled chloroplast, reduced internal starch grains, fuzzy andvacuolar mitochondrial cristae. Instead, The leaves contact with processing solutiondirectly, of which cell ultrastructure revealed reduced lamellae of chloroplast grana,incompact stroma lamellae, reduced starch granules, destroyed membrane structure andfollowed with its swelling and cracking; the mitochondria exerted aggregation, fuzzymembrane structure, internal vacuolization as its characteristic; cell wall adsorbed smallparticulate matter and the cell membrane degraded. The results showed that Chloroplastand mitochondrial damage is more serious, but relatively minor damage to the nucleus.In addition, another result showed that the extent of the damage of leaves contact withprocessing solution directly was more serious than the ones which contact withprocessing solution indirectly and roots system.