THE EFFECTS OF Fe ON THE GROWTH AND THE ACTlVITIES OF SOME ENZYMES IN THE ROOTS OF LETTUCE AND MUSTARD IN HYDROPONIC CULTURE

This study reported the effects of Fe in the nutrient solutions with various levels,0,2.8,5.6,8.4,11.2 and 14.4 mgFe/L on the growth,yield,Fe content in plants andthe activities of catalase and peroxidase in the roots of lettuce and mustard ina hydroponic system. The results showed that the yields of the two crops werethe highest when Fe concentration were 2.8 and 5.6 mgFe/L,respectively.The yieldsof both crops decreased if Fe increased further.Moreover,when the Fe levelswere above 2.8 and 5.6 mgFe/L for lettuce and mustard,respectively,lettuceshowed severe Fe toxic symtoms,but mustard only showed reduce yield.Belowthe optimum Fe level,the vegetable(mustard) with higher Fe content in the shootthan in the root was sensitive to Fe deficiency,but could tolerate Fe toxicity.The vegetable(lettuce)with higher Fe content in the root than in the shoot wassensitive to Fe toxicity but unlikely to show Fe deficient symtoms. Under the sameFe level at which plants did not show severe Fe toxic symptom,the vegetable(mustard)with higher activities o f peroxidase and catalase in the root seemed toshow poor tolerence to low Fe, but could tolerate high Fe. Lettuce with loweractivities of both two enzymes in the root could tolerence to low Fe and likelyshow Fe toxic symptoms. The activities of the two enzymes,however,did notdecrease with Fe toxicity.