Response To Salinity In Rice: Comparative Effects Of Osmotic And Ionic Stresses

Abstract

: The effects of the osmotic component of salt stress on rice cultivar IR64 were examined. Treatments were four combinations of two levels of osmotic stress at two developmental stages: medium-and highlevel stress applied at the vegetative and reproductive stages using salt (NaCl) and polyethylene glycol-6000 (PEG) as sources of osmotic stress. Both PEG and NaCl reduced the total above ground biomass and delayed flowering and maturity, with a longer delay observed with the high-level stress. The reduction in number of filled spikelets, 1,000-grain weight, and hence grain yield was significantly greater when they were applied during the reproductive stage than during the vegetative stage. The sodium concentration in plant tissues also increased in plants treated with NaCl, indicating that besides osmotic stress, plants were also subjected to ionic stress. Treatment with NaCl decreased the potassium concentration in plant tissues but did not cause significant differences in phenology, biomass accumulation, yield or N uptake compared with PEG. We concluded that the response of IR64 to NaCl was attributed to the osmotic component. These findings may be specific to IR64, which has a medium tolerance to salinity stress. Further studies are needed with longer stress durations to achieve a higher Na + concentration in plant tissues in several varieties with contrasting tolerance to salt stress to further establish the relative importance of osmotic versus ionic components of salt stress in rice.

Flooded rice yield as affected by levels of water salinity in different stages of its cycle

“…Likewise, Castillo et al (2007), based on a study that evaluated the effect of osmotic and ionic stresses on the rice variety IR64, observed that the higher the salinity level of the solution, the greater the delay of rice development, which reached 19 days. Whereas the range for sowing most of the cultivars used in the State of Rio Grande do Sul is 30 days.…”

“…In salt levels above tolerable by rice plants, the water salinity causes a decrease in tillering and increases spikelet sterility (Ehrler, 1960). Several studies with different genotypes and different locations and environments (Fageria, 1991;Zeng et al, 2001;Grattan et al, 2002;Rodrigues et al, 2005;Melo et al, 2006) have shown a linear relationship between the increasing levels of salinity and the decrease in the number of tillers, in addition to increasing the number of non-productive tillers (Castillo et al, 2007). Salt stress also causes a reduction of photosynthesis, which occurs due to decreased availability of CO 2 inside the leaf, by closing the stomata.…”

Estabelecimento do arroz irrigado e absorção de cátions em função do manejo da adubação potássica e do nível de salinidade no solo

“…Esse parece ter sido o caso nos tratamentos com PST de 10 e 20 %, mas não no de 5 %, que apresentou quantidade de material vegetal semelhante à do tratamento testemunha. Isso pode ter ocorrido pelo fato de, até determinado nível de salinidade, a compartimentalização do Na nos vacúolos poder evitar os efeitos deletérios desse elemento no citosol, mantendo o potencial osmótico da célula e minimizando o déficit hídrico em um ambiente salino (Castillo et al, 2007).…”

“…A maior concentração de Na no tecido, em função do cultivo de arroz em meio salino, impõe um estresse iônico sobre a cultura em adição ao estresse osmótico (Castillo et al, 2007). Neste estudo, esse fato é evidenciado pelos efeitos antagônicos entre os níveis de Na + adicionados ao solo e pela absorção de K pelo arroz (Quadro 8).…”

“…O excesso de Na + no solo pode causar a perda de íons K + em função da despolarização da membrana e substituição por íons Na + (Cramer et al, 1991). Os dois cátions têm átomos similares e os transportadores de K + são menos específicos em concentrações tóxicas de Na + (Castillo et al, 2007). A relação entre os íons K + e Na + é um indicador de tolerância à salinidade, pois reúne duas características desejáveis: alta absorção de K, necessária para os processos metabólicos e o ajuste osmótico, e a absorção de Na, como um indicador do nível de estresse (Garcia et al, 1997).…”