Biochemical Markers and Nutrient Constraints Diagnosis in Citrus: A Perspective

ABSTRACT

Mineral deficiencies are well-established causal factor(s) for sub-optimum production in citrus. Identifying nutrient constraints based on morphological symptoms or in combination with leaf/soil analysis is often misleading, especially with reference to remediating the nutritional problems of a standing crop. The task becomes further confounded by other co-factors under the conditions favoring the occurrence of multi-nutrient deficiency. Important biochemical markers for various nutrient deficiencies include: ribulose-1,5 biphosphate carboxylase (RuBPCase), nitrate reductase, and glutamate dehydrogenase for nitrogen (N) deficiency; citrate synthetase, aconitase, phosphoenol pyruvate kinase, and glutamic oxaloacetic transminase for phosphorus (P) deficiency; diesterase, acid invertase, arginine decarboxylase, and N-carbamyl putrescine aminohydrolase for potassium (K) deficiency; pyruvate kinase and succinate dehydrogenase for calcium (Ca) deficiency; invertase for magnesium (Mg) deficiency; adolase and aconitase for iron (Fe) deficiency; catalase for manganese (Mn) deficiency (higher peroxidase activity under Mn deficiency is differentiated from Fe deficiency); carbonic anhydrase and nitrate reductase for zinc (Zn) deficiency; and phenylalanine ammonia lyase and nitrate reductase for boron (B) and molybdenum (Mo) deficiency, respectively. These markers have also shown some promise in establishing the physiological basis of tolerance of Satsuma mandarin (Citrus unshiu Marc.) against Mn and aluminum (Al) toxicities involving the Mn-oxidative pathway and complexation of calmodulin protein with Al³⁺ ions, respectively.

Keywords:

• nutrient deficiency
• biochemical marker
• citrus nutrition
• toxicity