IS THERE A RELATIONSHIP BETWEEN FERRIC-CHELATE REDUCTASE ACTIVITY IN ROOTS OF PONCIRUS TRIFOLIATE AND LEAF CHLOROPHYLL CONTENTS?

Poncirus trifoliata is a citrus rootstock very sensitive to Fe deficiency. This deficiency is very common in crops grown in calcareous soils due to the detrimental effect of bicarbonate ion. Higher plants have distinct behaviours when faced with Fe chlorosis, and several mechanisms may be activated under Fe shortage. The aim of this study was to investigate the activity of ferric-chelate reductase (FC-R), a key enzyme in Fe uptake, and to verify whether relationships with leaf chlorophyll contents could be established. Plants were grown in nutrient solutions without Fe (0 µM Fe), with 1 µM Fe, with 120 µM Fe and with 120 µM Fe plus CaCO₃ (1 g L^-1). Total leaf chlorophyll in young and mature leaves was determined using a calibration model based on a relationship between SPAD readings and concentration of chlorophyll (r²=0.95; P<0.01). The activity of FC-R was determined in roots apexes and several biomass parameters in shoots (number of leaves, height, dry and fresh weight) and roots (dry and fresh weight) were evaluated at the end of the experiment. The activity of FC-R increased in plants grown without iron (0 µM Fe). The results about the relations between root FC-R and leaf chlorophyll are discussed.