Daniel Teixeira Pinheiro

Differential physiological responses in rice upon exposure to excess distinct iron forms

Background and aimsRice can be cultivated in highlands, which can expose it to iron deficiency, or under irrigation, which can lead to iron toxicity and lower productivity. This study aimed to investigate the strategies used by rice plants under different divalent and trivalent sources of iron excess.MethodsRice plants from a lowland and upland cultivar were grown in nutrient solution with toxic concentrations of ferrous or ferric iron. A mineral nutrient quantification and anatomical analysis were performed on leaves and roots. Physiological damage was assessed by leaf photochemical parameters and lipid peroxidation. Expression levels of genes related to iron homeostasis were analyzed.ResultsMore pronounced nutritional deficiencies, oxidative stress and physiological damage were observed in plants exposed to toxic levels of ferrous iron. Ferritin expression increased in leaves of both cultivars under ferrous or ferric iron excess.ConclusionsWe showed that sulfate iron was more toxic to the two rice cultivars even though this iron source was less translocated in the plant. Trivalent iron complexed to citrate is easily translocated through rice plants, but it is less toxic than the divalent iron. Rice plants are able to cope with this iron overload by keeping photosynthetic apparatus working properly.

TROPICAL RICE CULTIVARS FROM LOWLAND AND UPLAND CROPPING SYSTEMS DIFFER IN IRON PLAQUE FORMATION

In iron toxic wetlands, ferric hydroxide is commonly deposited on rice roots. This study aims to to evaluate the differences in iron plaque formation in rice cultivars from different cropping systems. Thirty days old seedlings of Brazilian rice cultivars from the lowland cropping system (‘BRS Atalanta’ and ‘Epagri 107’) and upland cropping system (‘Canastra’) or both systems (‘BRSMG Curinga’) and the cultivar ‘Nipponbare’ were exposed to iron excess [4 mM iron sulfate heptahydrate (FeSO4.7H2O)] for seven days in nutrient solution. It was observed iron plaque formation and ruptures of the root epidermal cells. The lowland cultivars showed higher Fe content in iron plaque. Iron stain was detected in the root hairs, epidermis, hypodermis, and exodermis. The root exodermis may be contributed to prevent the deposit of iron in the cortex of the lowland cultivars and in the cultivar ‘BRSMG Curinga’. It was observed in plants with iron plaque formation significant reductions in the shoot content of phosphorous, manganese and magnesium due to different causes. The differences in iron plaque formation among the cultivars might be an indicative of variations in exodermis selectivity, root oxidative capacity, and iron nutrition mechanisms.

Germination of melon seeds under water and thermal stress

Seeds vigor can influence seed performance under stress conditions. The objectives of this study were to evaluate the effect of water and thermal stress on germination and performance of melon seedlings, and to verify if germination under stress conditions is an efficient parameter to evaluate the vigor of these seeds. Four lots of ‘Golden Mine’ melon had their initial quality characterized by germination, first count, accelerated aging and seedling emergence tests. Germination under water stress was performed on a paper moistened with PEG 6000 solution at 0.06, -0.3, -0.6 and -0.9 MPa. The percentage and speed of germination, length and dry mass of the seedlings were evaluated. For the thermal stress experiment, cold test and germination at sub(15 oC) and supra-optimal (35 oC) temperatures were performed, as well as at the ideal temperature (25 oC). The germination of melon seeds under water stress induced by PEG 6000 at -0.3 and -0.6 MPa is an efficient method to detect differences in the physiological potential of lots of melon seeds, but these differences disappear under severe water stress (-0.9 MPa). Germination under sub-optimal temperatures also allows to identify differences in seeds performance and to classify them according to the vigor level.