锰胁迫对甘蔗幼苗缺铁和失绿的影响

摘要

近年来，甘蔗主产区的甘蔗幼苗出现严重的缺铁失绿问题，影响了我国甘蔗生产及食糖安全。为了揭示锰诱导甘蔗幼苗缺铁失绿机制，该研究采用水培试验法，对过多锰诱导的甘蔗幼叶失绿及其与铁素营养的关系进行了探讨。结果表明：过多锰胁迫下随着甘蔗中锰含量的增加，幼叶明显失绿。250、500、750μmol .L-1处理10 d 后，幼叶中的叶绿素含量分别从对照处理的1．71 mg.g-1 FW 下降至0．86、0．85、0．64 mg.g-1 FW。过多锰抑制甘蔗对铁的吸收，每株植株对铁吸收量(3．22~4．40 mg)显著减少。幼叶中铁含量(116．8~128．6 mg.kg-1 DW)也随着锰处理浓度的增加而显著降低。250~750μmol.L-1处理的甘蔗幼叶中铁的含量仅相当于对照处理的89．4％~81．2％。相反，锰处理后根和茎中铁的含量却显著增加。锰胁迫下幼叶中活性铁含量和活性铁与全铁比值(0．14~0．21)也显著降低。高锰胁迫下，幼叶中的活性铁含量(4．1~6．9 mg.kg-1 FW)相当于对照处理的25．5％~55．2％。相关分析结果显示，锰胁迫下的甘蔗叶片中活性铁含量与叶绿素含量呈显著的正相关；锰处理后幼叶中活性铁与锰含量的比值从对照的0．71下降至0．04~0．01。这说明过多的锰可诱导甘蔗幼叶失绿，而失绿与过多的锰胁迫下甘蔗对铁的吸收、运输受阻及铁的钝化有关。%The main sugarcane production areas of China have been suffered from sugarcane seedlings chlorosis for several years,which affected sugarcane production and threatened sugar security of China.Manganese (Mn)-induced chlorosis and its relationship to iron nutrition in sugarcane seedlings were investigated by hydroponic experiments to elucidate mechanisms for the chlorosis in plants.The results indicated that a significant chlorosis symptom was exhib-ited on young leaves of sugarcane seedlingswith the increase of Mn content in sugarcane under excessive Mn stress. Chlorophyll content in young leaves decreased from 1.71 mg.g-1 FW (control)to 0.86,0.85,0.64 mg.g-1 FW,re-spectively,after the sugarcane seedlings were exposed to 250,500 or 750 μmol.L-1 Mn solution for 10 d.Excess Mn inhibited iron (Fe)acquisition by sugarcane seedlings,which resulted in significant decrease in Fe acquisition rate (3.22-4.40 mg per plant).Fe content (116.8-128.6 mg.kg-1 DW)in young leaves decreased significantly with the increase of Mn-treatment concentration.After the treatment with 250-750 μmol.L-1 Mn,Fe content in the leaves was equal to 89.4%-81.2% of that in control.On the contrary,excess Mn resulted in significant increase in Fe con-tent in roots and stems.Moreover,both active iron content [Fe (H)]and the ratio of Fe (H)to total Fe (0.14-0.21)in young leaves under Mn stress declined significantly.Active iron content [Fe (H),4.1-6.9 mg.kg-1 FW] in the leaves was equated to only 25.5%-55.2% of that in control.The results of correlation analysis showed that chlorophyll content was positive related to Fe (H)in the leaves under Mn stress.On the other hand,the ratio of Fe (H)to total Mn in young leaves after the treatment with Mn declined to 0.04-0.01 while that in control was 0.71. These results indicated that excessive Mn could induce the chlorosis in sugarcane seedlings,and the inhibition of ac-quisition,transportation and activation of Fe by Mn are involved in the induction of the chlorosis.