Studies On Characteristics Of Uptake,translocation And Accumulation Of Cadmium In Rice

Cadmium (Cd) is one of deleterious and nonessential heavy metals for both plants and animals, andits easily entrance into the food chain through the soil-plant system will threaten human's health. Rice isone of the most important crops in China and it has been shown quite strong cadmium enrichmentability, besides, the farmland affected by Cd pollution is growing, so the rice security issues havebecome increasingly prominent. Consequently, it's utterly imperative to guarantee rice production safetythrough exploring the differences and their mechanisms of Cd absorption, transport and accumulationamong different rice types of Cd accumulation, then providing important theoretical basis for breedinglow Cd accumulation varieties and controlling grain Cd pollution. In the thesis, we chose two differentCd accumulation rice cultivars',Zhenshan97B'(low Cd in grains)and'Miyang46'(high Cd in grains,then investigated the characteristics of root Cd-uptake, xylem transport at seeding stage. Meanwhile, wealso investigated the regularity of Cd distribution, accumulation at rice different growth stages.Furthermore, phytochelatins and other thiol-containing compounds were analysed in the different partsof Zhenshan97B at the filling stage. The major results were summarized as follows:1.The Cd uptake ability of root apoplast pathway is basically the same for Zhenshan97B andMiyang46at seeding stage, and represented the linear concentration-dependency in both cultivars.While the symplastic Cd uptake ability of Zhenshan97B was significantly higher than Miyang46, andthis pathway showed a saturable trend in both cultivars.2. The relationships between Cd and Zn uptake in roots were varied due to cultivars at seedingstage. Cd enhanced Zn uptake in root for Miyang46, while Zhenshan97B showed in an opposite wayexcept under10μM treated concentration. Furthermore, the influence degree was different due tocultivars and Cd treated concentration.3. The Cd concentration in the stem was extremely positive correlation with that in the xylem sap.On the one hand, the transfer speed of Cd from root to shoot speeded up and the transfer amount of Cdincreased with the extension of time for two cultivars. However, the transfer speed and transfer amountof Miyang46were significantly greater than those of Zhenshan97B except0~1h, and the differencesbetween two cultivars increased with the extension of time. On the other hand, the transfer speed of Cdfrom root to shoot speeded up with the increasing of Cd treated concentration for two cultivars, and thetransfer speed increased slowly under moderate Cd treated concentration (0~5μM), besides, thedifference between two cultivars was small, while increased steeply under high treatedconcentration(5~20μM), and the difference between two cultivars increased at the same time. ABAtreatment could significantly reduced the transpiration and Cd accumulation in the stems of Miyang46and Zhenshan97B, and the decrease magnitude of transpiration of Miyang46was17.0%higher thanthat of Zhenshan97B, while decrease magnitude of Cd accumulation in the stems was just4.2%higherthan that of Zhenshan97B.4. The toxic effects of Cd on Zhenshan97B was weaker than that on Miyang46. On the one hand,the inhibitory effect of Cd on Miyang46plant height mainly occurred at seeding stage and tillering stage, while Zhenshan97B mainly at tillering stage, except for no difference at other stages for bothcultivars respectively. Furthermore, the inhibitory effect of Cd on Miyang46was more obvious than onZhenshan97B. On the other hand, the inhibitory effect of Cd on Miyang46dry weight of abovegroundmainly occurred at seeding stage to heading stage, while Zhenshan97B mainly at tillering stage, and theinhibitory effect of Cd on Miyang46was more obvious than on Zhenshan97B.5.The orderliness of Cd accumulation and distribution were studied with Miyang46and Zhenshan97B in the whole growth period. The results showed that the order of concentration of Cd wasroot>stem>leaf>grain for both cultivars. Meanwhile, Cd was mainly distributed in the root at thevegetative stage, and gradually transferred to aboveground part along with the development of maturity.The net Cd accumulation of whole plant and aboveground part in the whole growth period for bothcultivars was in a order: heading to maturation stage>transplanting to tillering stage>tillering to headingstage, and the Cd accumulation in Miyang46was always higher than that in Zhenshan97B significantly,except for the filling to maturation stage. Furthermore, the largest difference of Cd accumulation ofaboveground part occured in the heading to filling stage between Miyang46and Zhenshan97B. The Cdaccumulation rate of xylem increased firstly and then decreased in the whole growth period for bothcultivars, and reached their maximum in the filling stage respectively, when the largest differenceoccured between Miyang46and Zhenshan97B. Besides, the Cd accumulation rate of xylem remained ata high level during the entire heading to maturation stage for both cultivars. The Cd accumulation rateof phloem decreased firstly and then increased in the whole growth period for both cultivars, andreached their minimum in the heading stage, respectively. But increased sharply from filling tomaturation stage for both cultivars. Besides, the Cd accumulation rate of Miyang46phloem washigher than that of Zhenshan97B all the time throughout the whole growth period, especially duringfilling stage to maturation stage.6.In the whole growth period, the Cd accumulation rate of xylem was significantly positivecorrelation with the Cd accumulation in stem, as well as Cd accumulation in leave for twocultivars.During filling to maturation stage, the Cd accumulation rate of phloem, Cd accumulation inwhole plant and Cd accumulation in aboveground showed a significant correlation with concentration ingrain for two cultivars, respectively.7.There were just small amounts of Cys and GSH in rice under normal condition, while rice plantwould synthetize a large number of PC2, PC3and their sub-isomers, and the content and types of themwere different between different organs. It was found that the PCs in root of rice are PC2, iso-PC2(ser),iso-PC2(Glu), des-γGlu-PC3and des-Gly-PC3; the PCs in stem are iso-PC2(ser), iso-PC2(Glu),des-γGlu-PC3, des-Gly-PC3and iso-PC3(ser); the PCs in leaf are iso-PC2(β-Ala), iso-PC2(ser) andiso-PC2(Glu). Furthermore, the order of the total content of PCs was: root>stem>leaf.