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Ciência Rural

Print version ISSN 0103-8478On-line version ISSN 1678-4596


GOMES, Fernando Teixeira; PEREIRA, Gilmara Duarte; BORGES, Arnaldo Chaer  and  MOSQUIM, Paulo Roberto. Photosynthesis in alfalfa (Medicago sativa L.) under phosphate suppression and ressuply. Cienc. Rural [online]. 2003, vol.33, n.5, pp.821-828. ISSN 0103-8478.

This work evaluated the phosphate (Pi) suppression and ressupply on photosynthesis and photochemical efficiency from Medicago sativa plants cv. Florida 77, in different growth stages (V3 and V4) and reproductive (R6 and R8). The experiment was performed in a greenhouse, the plants being cultivated in HOAGLAND & ARMOND (1950) nutritive solution containing 0,14mmol L-1 of Pi. Pi suppression for ten days reduced Pi levels in sampled leaves, in all growth stages. However, with the re-supply only in the vegetative stages the values were similar to the control treatments. Photosynthesis per foliar area in all growth stages decreased with Pi suppression. In general, Pi ressupply into the nutritive solution resulted in recovery of photosynthesis, except for V3 plants, indicating that the suppression period did not cause permanent damage to the photosynthetic apparatus. Levels of photosynthetic pigments and the photosystem II (PS-II) photochemical efficiency evaluated as the Fv/Fm ratio were not altered when plants were submitted to Pi suppression. These results show that electons transport through PS-II did not limit photosynthesis in the sampled leaves under Pi supression, suggesting that Pi suppression caused a more pronunciated effect in the biochemical step of photosynthesis.

Keywords : nutritive solution; photochemical efficiency; CO2 assimilation.

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