The effect of genome duplication on seed germination and seedling growth of rice under salt stress.

Polyploidy was widely believed to facilitate increased plant adaptability to environmental extremes. Reports of the effect of genome duplication on rice development under salt stress are rare. In this study, tetraploid rice cultivars and the diploid ancestors were subjected to six levels of salinity, and the effects of genome duplication at seed germination and at the seedling growth stage were investigated. The results suggest salt stress has a large negative impact at both stages but genome duplication has important positive roles in modulating the response to salt stress in different rice cultivars. The germination rate of four tetraploid rice cultivars was generally higher than those of diploid cultivars under salt stress; in particular, cultivars Nipponbare-4x and HN2026-4x have >50% of the germination rate in 150 mM NaCl. The growth of all diploid and tetraploid cultivars studied was inhibited by salt stress. The mortality rates of tetraploids were all lower than those of diploids; the low mortality of HN2026-4x (12.3%) and Nipponbare-4x (12.6%) showed potentially better salt tolerance. The amount of free proline in different tetraploid rice cultivars varied greatly and was increased compared to that in the diploid cultivars. The difference of soluble sugar content under salt stress, was not significant between tetraploid and diploid cultivars. Malonyldialdehyde accumulated in the leaves of tetraploid rice was significantly lower than that of diploid cultivars under salt stress, the content of MDA in Nipponbare-4x (55.3 mumol g-1) under salt stress was the lowest among all cultivars, indicating membrane damage was the least.