Study On Phenomenon Of "Iron Chlorosis Paradox" In Leaf Nutritional Diagnosis Of Kuerle Fragrant Pear (Pyrus Bretschneideri Rehd)

Most fruit trees grown on calcareous soils suffer from lime-induced iron (Fe) deficiency showingcharacteristic symptoms known as Fe chlorosis (yellowing) in leaves. Recent years, decrease in yield andquality and declination of tree body of negative consequences caused by chlorosis have seriously affectedlocal fruit grower’s positivity of planting and the development of this characteristic industry. In this study,with a view the phenomenon of “iron chlorosis paradox”, based on using the research production of KuerleFragrant Pear for reference, researched the microstructure and ultrastructure of Fragrant Pear leaves, probedeffective using of iron forms and the position of "iron pool" in leaves, tried to find out anothercharacterization method of total iron and active iron content in Fragrant Pear leaves. The results are asfollows:1．Leaf thickness, palisade tissue thickness and cell tense ration of chlorotic leaves were significantlylower than those of healthy leaves. The thickness of upper and lower epidermis was remarkable thickerthan those of healthy leaves. The arrangement of the cells in vascular bundles was in disorder. The vesselswere distorted seriously and the caliber of the vessel became shorter. The chloroplasts of chlorotic leafdistorted and their sizes became smaller obviously. Iron-deficiency influenced the formation of grana in achloroplast. The arrangement of the cells in spongy tissue was loosen, the organelles of cells in thechlorotic leaves was broken, even cavity appeared in the whole cell. External expression of leaf ironchlorosis was controlled by changes of leaf inside and organizational structure.2．Three types shoots revealed common seasonal change of single peak curve in the chlorophyllcontent. The highest chlorophyll content was tested in the leaves on the spurs not bearing fruit, higher onthe spurs bearing fruit and the lowest on the middle extending shoots. Chlorophy (a/b) value of leaves ondifferent shoots showed similar double peak curve of high-low-high. Chlorophy (a/b) value of chlorotictrees leaves were higher than the vaule of healthy trees leaves. Chlorophy (a+b) vaule of three types shootsof healthy trees were more than twice as high as chlorotic tree.3．“Iron pool”of leaf was in the apoplast. Apoplastic iron content accounts for58%-64%of total ironcontent. Cells of chlorotic leaf cann’t absorb iron in apoplast that result in chlorosis.4．Lack of active iron was the first reason for chlorosis of the pear leaves. Active iron was effectiveusing of iron forms,it can also characterize the iron content of the leaves. Compared to green leaves, totaliron content of chlorotic leaves was not low, indicating iron chlorosis was a physiological disorder. Totaliron content based on dry leaf weight cann’t characterize the iron nutritional status of pear tree, howere, itcan help to make a judgment for the correction of iron chlorosis.If leaf weight per area can characterize thetotal and active iron content,“iron chlorosis paradox” would be avoided as the calculate method.