Studies On Physiological Mechanism In Cadmium Accumulation And Tolerance And Its Difference Among Genotypic Of Rice

Cadmium (Cd) is one of the most deleterious heavy metals to both plants andanimals, and its contamination in soil has turned into one of the most troubleagricultural and environmental issues worldwide. Genetic variation in Cd uptake andtolerance exists between and within rice varieties. Consequently, it is one of the bestcost-effective and efficient approaches to develop Cd-tolerant genotypes with low Cdaccumulation in brown so as to guarantee rice production safety and make full use ofnatural resource. This investigation was carried out to study the physiologicalmechanism of genotypic difference in Cd- uptake, accumulation and tolerance of riceand detrimental effects of Cd on growth and yield formation, based on the research ofgenotypic variation of rice, by using Cd pot experiments,hydroponics' experimentsand so on. The major results were summarized as follows:1. Effect of cadmium on rice seeds germinationEffects of cadmium on rice seed germination were studied with 319 varietiestreated by 10mg/L Cd²⁺ concentration. The results showed that 1) percentage ofgermination effects were trivial, and roots development restrained evidently stronglythan to the sprout, 2) germination of different rice varieties response to Cd²⁺ weredifference, the sequence was in a order: Conventional rice(Japonica rice)＞hybridrice(Indianica rice)＞conventional rice(Indianica rice). 3) the root length and numberof two-lines sterility restrained evidently strongly than to the three-lines sterility (Froot length=11.29, P＜0.05; F root number =7.42, P＜0.05); 4) and the 319 varietieswere clustering to 3 types by response to Cd²⁺, endurance type, middle type, sensitivetype.2. Genotypie difference of cadmium contents in brown ricePot experiment was conducted to investigate the Cd contents in brown using 47rice cultivars, which were divided to 7 types. The results showed that the rice cultivarstested differentiated in brown of Cd contents. The Cd concentrations in brown ricewere varied from 0.428～2.558 mg·kg^-1. The Cd content of brown varied in ricegenotype, the sequence was in a order: special rice＞early conventional rice(Indianica rice)＞three line hybrid rice(Indianica rice)＞two line hybrid ric(Indianica rice)e＞lateconventional rice(Indianica rice)＞conventional rice(Japonica flee)＞conventionalrice(Javaniea flee). Meanwhile the cadmium (Cd) contents in brown of 130 ricevarieties were analyzes. The results showed that: 1) genotypic difference existed in Cdcontents. Indianiea rice had higher concentration on Cd in brown than Javanica rice,and the sticky rice higher than mueosity flee, early-rice higher than middle-rice,late-rice had low concentration of Cd content in brown. And Cd content of varietiesthat came from different region were variance, the sequence was in a order:South-Asia＞China＞Korea and Japan. 2) Significantly positive correlation betweenCd contents to protein contents in brown, and it significantly negative correlation withCa contents was found. Meanwhile significantly positive correlation between Cdcontents in brown to root at seeding stage were confirmed, the same relation found atripen stage of rice. 3) The 130 varieties would class to four types by Cd content andtolerance: hi-tolerance and low-contents; hi-tolerance and hi-contents; low-toleranceand low-contents; low-tolerance and hi-contents.3. Accumulation and distribution of cadmium in rice and its genotypic differenceThe orderliness of Cd accumulation and distribution were studied with 130 ricevarieties. The results showed that the reserves of Cd in root were more than in thestem and leaf and grain. The Cd accumulation of Hi-Cd-eontent varieties wassignificantly much more than the Low-Cd-eontent, and the three-lines-sterile muchthan the two-lines-sterile. Significantly positive correlation between the Cdaccumulation and number of effective spike of individual plant, the same as to theweight per 1000 of rice were confirmed, but its not significantly to yield. Furthermore,significantly positive correlation was observed on the Cd accumulation to the biomassand Cd contents on root of rice.4. Subcelular distribution of cadmium in rice and its genotypie differenceIn an effort to understand the biological process of Cd bioaccumulation, asolution culture experiment combined with subcelluar fractionation were carded outto investigate subcelluar distributions of Cd in roots and leaves of rice. Twohi-Cd-tolerance and low-Cd-contents cultivars (HTLC) and two low-Cd-toleranee andhi-Cd-eontents cultivars (LTHC) were compared. 1) Accumulation of Cd in cell waspositive correlation with concentration of Cd in solution, and the accumulation of Cdin roots cell was higher than in the leave's. Cd was mainly distributed in cell wall, and high Cd concentration in solution mean to high ratio of Cd content in cell wall. 2)There was difference of Cd concentration between HTLC and LTHC cultivars.Contents of Cd in roots and leaves cell of HTLC cultivars were significantly lowerthan LTHC cultivar's. In the subcelluar fractions, contents of Cd in chloroplast (orplastid in root), mitochondrion and nucleolus of HTLC cultivar were lower thanLTHC cultivar's, but higher than LTHC cultivar's in the fraction of solublecomponent. 3) Contents of Zn and Fe in cell of roots and leaves were fewdifferentiates in different treatments under low concentration of Cd, but itssignificantly higher in high concentration of Cd treated than low concentration.Meanwhile Contents of Zn and Fe in cell of roots and leaves of HTLC cultivars weresignificantly lower than LTHC cultivar's.5. Effects of cadmium stress on physiological mechanism and its genotypicdifferenceEffects of physiological mechanism under different Cd concentration stresses inrice by solution culture experiment were investigated, and it's differentiate were alsodiscussed. 1) The net photosynthesis rate, stomatal conductance and transpiration rateof leaves were declined to go with Cd concentration stresses augmentation, butintercelluar CO2 concentration was ascended. Chlorophyll contents of leaves weredeclined, but the chlorophyll a/b value was ascended went with Cd concentrationstresses augmentation. Effects of different Cd concentration stresses onphotosynthesis under different photons density flux were investigated. The darkrespiration rate, apparent quantum efficiency and maximum net photosynthesis ratesignificantly declined were observed under different treatments, but lightcompensation points were significantly augment. 2) Malondialdehyde (MDA)contents of flag leaves were significantly ascended under 1.0 mmol／L Cd2+treatment, and there were higher content of MDA in flag leaves of LTHC cultivarsthan HTLC cultivar's. 3) Effects of different concentrations of Cd on nitrogen contentin roots and leaves were estimated. It found that the nitrogen content in roots andleaves were descended to go with Cd concentration stresses augmentation, and thedescended range of reduction of LTHC cultivars were exceed over HTLC cultivar's.