Respostas ecofisiológicas de Cecropia hololeuca e Carica papaya ao estresse por ferro

Abstract

Iron is an essential nutrient for plant development, but when in excess it can lead to increased oxidative stress, interference with metabolism and physiological damage that will culminate in growth losses. Such adverse conditions can now be easily found in river beds and regions near areas contaminated by iron accumulation. Thus, the aim of this study was to verify the possible ecophysiological changes in germination and initial growth of the tree species Carica papaya and Cecropia hololeuca submitted to planting under toxic iron conditions. Both species were subjected to concentrations of 0.045, 4 and 8mM applied in the form of ferrous sulfate and FeEDTA. The seeds were germinated in a BOD germination chamber, using a constant temperature of 25 ºC and a photoperiod of 12h / 12h. The variables analyzed were the germination percentage (% G), germination speed index, length of the aerial part, length of root, fresh mass and dry mass. For the initial development analysis, the seeds were sown in 0.5L polyethylene pots, maintained in Hoagland's solution at half ionic strength and pH 5.0 and the following variables were analyzed: leaf area, stem length, root length, fresh weight, dry weight, quantification of chloroplast pigments, analysis of chlorophyll fluorescence, analysis of element contents via scanning microscopy and EDS. The activity of antioxidant enzymes SOD, CAT, POX was verified for young seedlings. Iron stress affected the germinative behavior of both species, with decreases in the germination rate, root length, fresh and dry mass of the root and shoot. In young seedlings, the increase in iron levels brought fluctuations in the content of chloroplasty pigments, and in photosynthetic activity, in addition to damage to root and aerial growth, as well as a drop in leaf area values and biomass accumulation. Iron was mobile in plant tissues and reduced the absorption of potassium and calcium in stressed seedlings. The application of ferrous sulfate and FeEDTA did not cause a significant increase in the activity of the enzymes SOD and CAT. FeEDTA treatment increased MDA concentration and POX enzyme activity. The damages caused by the accumulation of iron in the germination and initial development of the species Carica papaya and Cecropia hololeuca show damage to the growth and establishment of these species in areas contaminated by the metal.