BackgroundSalinity is a stressful environmental factor that limits the productivity of crop plants, and roots form the major interface between plants and various abiotic stresses. Rice is a salt-sensitive crop and its polyploid shows advantages in terms of stress resistance. The objective of this study was to investigate the effects of genome duplication on rice root resistance to salt stress.ResultsBoth diploid rice (HN2026-2x and Nipponbare-2x) and their corresponding tetraploid rice (HN2026-4x and Nipponbare-4x) were cultured in half-strength Murashige and Skoog medium with 150 mM NaCl for 3 and 5 days. Accumulations of proline, soluble sugar, malondialdehyde (MDA), Na+ content, H+ (proton) flux at root tips, and the microstructure and ultrastructure in rice roots were examined. We found that tetraploid rice showed less root growth inhibition, accumulated higher proline content and lower MDA content, and exhibited a higher frequency of normal epidermal cells than diploid rice. In addition, a protective gap appeared between the cortex and pericycle cells in tetraploid rice. Next, ultrastructural analysis showed that genome duplication improved membrane, organelle, and nuclei stability. Furthermore, Na+ in tetraploid rice roots significantly decreased while root tip H+ efflux in tetraploid rice significantly increased.ConclusionsOur results suggest that genome duplication improves root resistance to salt stress, and that enhanced proton transport to the root surface may play a role in reducing Na+ entrance into the roots.

The meiotic processes of most polyploid rice (Oryza sativa) are genetically abnormal, leading to low pollen fertility, which results in low seed set rates. Some polyploid meiosis stability (PMeS) lines with high seed set rates have been bred but their meiotic mechanisms remain unknown. In this study, we investigated the function of OsMND1 regulated polyploid rice meiosis. OsMND1 localized in the nucleus, and its expression level in panicles of PMeS line HN2026-4x was higher than in HN2026-2x and the other lines without the PMeS background. OsMND1's overexpression improved pollen fertility and viability, early normal embryo development and the seed set rate in Balilla-4x. However, OsMND1 RNAi in PMeS line HN2026-4x impeded pollen and embryo development significantly. The results of chromosome behavior analyses indicated that OsMND1 participates in stabilizing meiosis by maintaining the balance of pairing, synapsis and recombination during early meiosis. Many univalent, trivalent, and even multivalent systems appeared in the OsMND1 RNAi line, resulting in the presence of many lagging chromosomes. The outcome indicated that OsMND1 plays a critical role in stabilizing meiosis, improving pollen fertility and reducing early embryo abortions, ultimately increasing the seed set rate. Additionally, OsMND1 affected some key meiosis-related gene expression levels. These results raise interesting issues in polyploid breeding theory and application, which require integrated solutions in the future.