Effects of iron toxicity on osmotic potential, osmolytes and polyamines concentrations in the African rice (Oryza glaberrima Steud.)

The African rice species Oryza glaberrima is well adapted to iron toxicity frequently occurring under flooded conditions. Seedlings belonging to two cultivars differing in their level of resistance to iron stress (TOG 7105: resistant and IRGC 104047: sensitive) were grown in hydroponic culture for 2 weeks and treated with 0, 250 and 500 mg l−1 Fe2+. Iron concentration in roots was higher in the resistant cv. TOG 7105 than in the sensitive cv. IRGC 104047, while an opposite trend was recorded in laminae, thus suggesting that iron exclusion could be an efficient mechanism of iron resistance. Osmotic potential in laminae decreased to a higher extent in cv. IRGC 104047 than in cv. TOG 7105. Proline and soluble sugars concentrations increased in the iron-sensitive cv. IRGC 104047 only and remained unaffected in the resistant one. Polyamine concentrations were always higher in cv. TOG 7105 than in cv. IRGC 104047, whatever the organ and the duration of treatment. Iron treatment stimulated ethylene biosynthesis to a higher extent in TOG 7105 than in IRGC 104047. These results are discussed in relation to the physiological strategies involved in iron stress resistance in African rice.