Effects Of Iron Stress On Mineral Elements Contents In Leaves And Related Genes Expression

Iron is one of the essential trace elements for plants and plays an extremely important role in many physiological processes of plant such as the photosynthesis, respiration, protein and nucleic acid synthesis and so on. The region of the Yellow River Old Yalley is the main pear production area in China, where the main cultivar ’Dangshansuli’pear (Pyrus bretschneideri Rehd.) is always showing the symptom of iron nutrition deficiency, which has a serious impact on the fruit yield and quality of ’Dangshansuli’pear.To discuss the effect of iron stress on the content of mineral elements, quantitative expression of relevant gene and chloroplast structure in leaves of ’Dangshansuli’pear, the chlorosis leaves with different degrees of iron-deficiency in ’Dangshansuli’pear were taken in the field as experiment materials. The content of full mineral elements were determined at each degrees of iron-deficiency and the correlation of iron with the others in the leaves were analyzed. Relevant genes about ferri iron storage and conversion were cloned by the rapid amplification of cDNA ends (RACE); and their expression levels were also analyzed by quantitative Real-time PCR (qRT-PCR). The structure differences between normal and chlorosis leaves were examined under the transmission electron microscopy.The main results had been achieved were as follows.1. In defferent degrees of iron deficiency leaves, there was a extremely significant positive correlation between Fe content and the content of Cu and Mo, of that the coefficients were all at0.998; there was a significant positive correlation between Fe content and the content of B, Cl, the correlation coefficients of which was0.985and0.968, respectively. It had been demonstrated that the leaf chlorosis on new shoot due to iron deficiency can influence the plant absorption of some other mineral elements.2. The grana in chloroplast were normally shaped and the lamellar of chloroplast were orderly arranged in the normal leaf; on the contrary, the grana were dissolved and the lamellar structure was destroyed into fragments in the chlorosis leaf due to iron-deficiency. It was postulated that the chloroplast structure of the chlorosis leaf would be distorted by the iron nutrition deficiency.3. The partial3’-end sequence of PbFerl、PbFer2、PbFer3、PbFer4and PbFdl gene had been amplified according to the instruction of TakaRa3’-Full RACE Kit; and the partial5’-end sequence of PbFer2and PbFd1gene had been amplified under the instruction of the User Manual of SMARTerTM RACE cDNA Amplification Kit. The full length of the PbFer2and PbFdl genes were obtained by splicing with the related partial sequences amplified. The results of bioinformatics analysis showed that the full length of PbFerl was1179bp, its coding sequence (CDS) covered798bp, encoded265amino acids putatively, including a5’-UTR of50bp and a3’-end untranslated region (UTR) of224bp.The full length of PbFer2was1052bp, its coding sequence (CDS) covered828bp, encoded275amino acids putatively, including a3’-end untranslated region (UTR) of224bp The full length of PbFer3was1103bp, its coding sequence (CDS) covered789bp, encoded262amino acids putatively, including a5’-UTR of15bp and a3’-end untranslated region (UTR) of299bp.The full length of PbFer4was1145bp, its coding sequence (CDS) covered816bp, encoded271amino acids putatively, including a5’-UTR of105bp and a3’-end untranslated region (UTR) of224bp.The the full length of PbFdl gene was704bp, its CDS was435bp, encoded144amino acids putatively, including a5’-UTR of59bp and a3’-UTR of210bp.4. There were significant differences in the expression level of Ferritin gene and Ferredoxin gene between the leaves with iron-deficiency degrees. In compareson with the normal leaf, the expression level of PbFer2increased in leaf with slight symptom of iron-deficiency, but it decreased as the degree of leaf iron-deficiency increased. The relative expression of PbFer1、PbFer3and PbFer4gene were both decreased when the symptom of iron-deficiency became severe. The relative expression of PbFdl decreased in leaf with slight iron-deficiency, increased slightly when the degree in leaf with moderate iron-deficiency, but it was still significantly lower than that of the normal leaf. The quantitative expression of PbFdl could decrease further as the leaf iron-deficiency got more severe.