Rootstock influence on iron uptake responses inCitrusleaves and their regulation under the Fe paradox effect

Background and aimsThis work evaluates the regulation of iron uptake responses in Citrus leaves and their involvement in the Fe paradox effect.MethodsExperiments were performed in field-grown ‘Navelina’ trees grafted onto two Cleopatra mandarin ×Poncirus trifoliata(L.) Raf. hybrids with different Fe-chlorosis symptoms: 030146 (non-chlorotic) and 030122 (chlorotic).ResultsChlorotic leaves were smaller than non-chlorotic ones for both dry weight (DW) and area basis, and exhibited marked photosynthetic state affection, but reduced catalase and peroxidase enzymatic activities. Although both samples had a similar total Fe concentration on DW, it was lower in chlorotic leaves when expressed on an area basis. A similar pattern was observed for the total Fe concentration in the apoplast and cell sap and in active Fe (Fe2+) concentration.FRO2gene expression and ferric chelate reductase (FC-R) activity were also lower in chlorotic samples, whileHA1andIRT1were more induced. Despite similar apoplasmic pH, K+/Ca2+was higher in chlorotic leaves, and both citrate and malate concentrations in total tissue and apoplast fluid were lower.Conclusion(1) The rootstock influences Fe acquisition system in the leaf; (2) the increased sensitivity to Fe-deficiency as revealed by chlorosis and decreased biomass, was correlated with lower FC-R activity and lower organic acid level in leaf cells, which could cause a decreased Fe mobility and trigger other Fe-stress responses in this organ to enhance acidification and Fe uptake inside cells; and (3) the chlorosis paradox phenomenon in citrus likely occurs as a combination of a marked FC-R activity impairment in the leaf and the strong growth inhibition in this organ.

Predicting the occurrence of iron chlorosis in grapevine with tests based on soil iron forms

<p style="text-align: justify;"><strong>Aims</strong>: Iron deficiency symptoms (leaf chlorosis and depressed growth) are common in grapevine growing on calcareous soils. The objective of this study was to investigate the relationships between these symptoms and the properties of Spanish vineyard soils.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Soils from thirty vineyards with leaf chlorosis were used to pot '110 Richter' rootstock for three seasons. Mean leaf chlorophyll concentration, as measured via SPAD, was positively correlated with the soil content in poorly crystalline Fe oxides, as estimated by extraction with various reagents, and negatively correlated with the contents in calcium carbonate equivalent and active lime. Iron deficiency affected plant growth but none of the measured growth variables was correlated with soil properties. The relationships between SPAD and acid ammonium oxalate-, citrate/ascorbateand unbuffered hydroxylamine-extractable Fe conformed to the linear-plateau model, from which clear-cut critical levels (345, 425 and 8 mg kg^-1, respectively) could be established. This was not possible with tests based on the alkalinity properties (e.g. the calcite ion activity product), the IPC (« Indice du pouvoir chlorosant »), and the DTPA-extractable Fe test, which generally exhibited a poor predictive value.</p><p style="text-align: justify;"><strong>Conclusion</strong>: Tests based on reagents capable of extracting, in part or quantitatively, the most reactive forms of soil Fe were useful to estimate the risk of Fe chlorosis in grapevine. Acid ammonium oxalate, citrate/ascorbate and unbuffered hydroxylamine were the best extractants for this purpose.</p><p style="text-align: justify;"><strong>Significance and impact of study</strong>: This study has shown the limited usefulness of tests based on the contents and reactivity of the soil carbonate to predict the occurrence of Fe chlorosis in grapevine; tests capable of estimating the contents of the labile soil Fe forms constitute the best alternative.</p>

Tolerance Response to Iron Chlorosis of Prunus Selections as Rootstocks

The use of rootstocks tolerant to iron deficiency represents the best alternative to prevent Fe chlorosis for peach production in calcareous soils. Early detection laboratory screening procedures allow the selection of new Fe-efficient rootstock genotypes. Seventeen Prunus rootstocks were tested for root ferric chelate reductase (FC-R) enzymatic activity, leaf SPAD values, and field performance. Some rootstocks were used as a reference to compare with new Prunus selections. Micropropagated plants were grown in hydroponic culture with half-strength Hoagland's nutrient solution containing 90 μm Fe(III)-EDTA as a control treatment. Plants were transferred to iron-free fresh solutions for 4 days and were thereafter resupplied with 180 μm Fe(III)-EDTA for 1 or 2 days. In vivo FC-R activity was measured in all treatments, i.e., control, Fe-deficient, and 180 μm Fe(III)-EDTA resupplied plants. The FC-R activity after Fe resupply was higher in Fe-efficient genotypes such as AdesotoPVP, FelinemPVP, GF 677, Krymsk 86™, and PAC 9921-07 than in the controls. No induction of FC-R activity was found in other genotypes such as Barrier, Cadaman™-AvimagPVP, PAC 9907-23, and PAC 9908-02. An intermediate response was observed in GarnemPVP, Gisela 5PVP, Krymsk 1PVP, Torinel™-AvifelPVP, VSL-2™, and PAC 9904-01. According to the induction of FC-R activity after Fe resupply, genotypes were classified as tolerant, moderately tolerant, or nontolerant to iron-induced chlorosis. These results were compared with SPAD values of plants grown under controlled conditions and in the nursery. Rootstocks that show high induction of FC-R activity also showed high or very high SPAD values in the field.