Maganese Induced Chlorosis Of Sugarcane Seedlings And Cause Analysis

Guangxi as the largest sucrose production base in China, the sugar yield has ranked first for many years over our country. However, most of sugarcane (Saccharum officinarum L) production areas in Guangxi have been suffered seriously from chlorosis for several years, which seriously affected the growth and sugar yield of sugarcane. Therefore, it is of great significance to solve this problem for ensuring sugar supply and security. Elucidation of mechanisms for sugarcane seedling chlorosis is the premise to solve the problem fundamentally. The mechanisms of manganese (Mn)-induced iron deficity chlorosis were studied in present study by hydroponic experiments to provide theoretical basis on solving the problem. The main results are as follows:1、Excess Mn affected the growth and significantly reduced biomass in sugarcane seedling. After24days treatment with250～750μmol·L-1Mn, biomass of sugarcane seedling decreased significantly. Moreover overground part was more sensitive to Mn.2、Excess Mn induced chlorosis of sugarcane seedling. After10days treatment, Mn resulted in interveinal chlorosis on young leaves, and chlorophyll content in young leaves reduced significantly. After24days treatment with Mn, Mn content and Mn absorbtion of young leaves increased significantly. Young leaves chlorophyll content decreased even more with the rise of Mn content, and young leaves chlorosis.3、Excess Mn inhibited iron absorbtion, transportation and activation, and iron deficity was the key factor affecting Mn-induced iron deficity.(1) After34d treatment with250,500,750μmol·L-1Mn, activitied iron content was6.87,6.67,4.12mg·kg-1FW, which relative to86.7～44.8%of those in the control (1μmol·L-1Mn) respectively. And the relationship between chlorophyll content and active iron in young leaves was significantly positive correlation. In addition, Mn induded a lower ratio of Fe(H)/Fe or Fe(H)/Mn.(2) Excess(250,500,750μmol·L-1) Mn inhibited iron uptake by sugarcane seedlings. Under excess Mn stress, iron absorbtion of sugarcane seedling were4.40～3.22g·plant-1(ROC22),4.07～3.80g·plant-1(GT21), decreasing by9.6%～33.9%,24.4%～29.6%as comparasion to that in the control respectively.(3) Excess Mn inhibited iron transportation to overground part, and reduced iron distribution in young leaves. Excess Mn reduced iron ratio of overground part to root content, and the ratio (3.18,2.58,2.19,2.06) decreased with the increase in Mn treated (1,250,500,750μmol·L-1) in ROC22. After Mn treatment, the iron in leaves relative to Fe in whole plants reduced from0.57to0.44～0.55. Furthermore, iron content in stem increased significantly after Mn treatment, but iron content in leaves decreased significantly.4、Under Mn stress, the content of reduction substance in young leaves decreased significantly which resulted in the decrease of iron activity. After Mn treatment, total phenol content in young leaves decreased significantly. Mn also induced a reduction of AsA, another reduction substance in leaves. And the relationship between phenol or AsA content with active iron content in leaves was significantly positive correlation. These results suggest that the decrease in active iron content in sugarcane seedling under excess Mn stress may result from the reduction of total phenol and AsA.5、There were significant different between cultivar in Mn-induced chlorosis. Under Mn effects on chlorophyll content in young leaves, plant growth and biomass in GT21were less smaller than those in ROC22. Although, Mn content in GT21was higher, but young leaves iron content and iron accumulation didn’t reduce after Mn treatment, while iron absorbtion and young leaves iron content decreased significantly in ROC22. In addition, under250μmol·L-1Mn treatment, activitied iron content in ROC22was higher than that of GT21. Total phenol content in GT21was higher than that of ROC22under higher Mn stress. And the content of NA, a Fe2+transporter, in GT21was also higher than that in ROC22. Besides,750μmol·L-1Mn activated POD activity in GT21leaves, but inhibited POD activity in ROC22. Thus, these reslutes imply that GT21is a cultivar to resistant Mn-induce chlorosis, and the resistance may attribute from higher absorbtion, transportation, accumulation, activation of Fe and stronger resistance to membrane lipid peroxida.