To gain a better understanding of salt stress responses in plants, we used a proteomic approach to investigate changes in rice (Oryza sativa) root plasma‐membrane‐associated proteins following treatment with 150 mmol/L NaCl. With or without a 48 h salt treatment, plasma membrane fractions from root tip cells of a salt‐sensitive rice cultivar, Wuyunjing 8, were purified by PEG aqueous two‐phase partitioning, and plasma‐membrane‐associated proteins were separated by IEF/SDS‐PAGE using an optimized rehydration buffer. Comparative analysis of three independent biological replicates revealed that the expressions of 18 proteins changed by more than 1.5‐fold in response to salt stress. Of these proteins, nine were up‐regulated and nine were down‐regulated. MS analysis indicated that most of these membrane‐associated proteins are involved in important physiological processes such as membrane stabilization, ion homeostasis, and signal transduction. In addition, a new leucine‐rich‐repeat type receptor‐like protein kinase, OsRPK1, was identified as a salt‐responding protein. Immuno‐blots indicated that OsRPK1 is also induced by cold, drought, and abscisic acid. Using immuno‐histochemical techniques, we determined that the expression of OsRPK1 was localized in the plasma membrane of cortex cells in roots. The results suggest that different rice cultivars might have different salt stress response mechanisms.

Maize is a major economic crop worldwide, with substantial crop loss attributed to flooding. During a stress response, programmed cell death (PCD) can be an effective way for plants better adapt. To identify flooding stress related PCD proteins in maize leaves, proteomic analysis was performed using two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) and mass spectrometry.

Natural resistance-associated macrophage proteins (NRAMPs) have been shown to transport a wide range of divalent metal ions, such as manganese (Mn), cadmium (Cd), and Iron (Fe). Iron is an essential micronutrient for plants and Fe deficiency can lead to chlorosis or decreased biomass. AtNRAMP6 has demonstrated the capability to transport Cd, but its physiological function is currently unclear. This study demonstrates that AtNRAMP6 is localized to the Golgi/trans-Golgi network and plays an important role in intracellular Fe homeostasis in the flowering plant genus Arabidopsis. GUS tissue-specific expression revealed that AtNRAMP6 is highly expressed in the lateral roots and young leaves (three to four top leaves) of Arabidopsis. Moreover, knocking out AtNRAMP6 was shown to impair lateral root growth without having a differential effect on the main root under Fe-deficient conditions. Lastly, the expression of AtNRAMP6 was found to exacerbate the sensitivity of the yeast mutant Δccc1 to an excessive amount of Fe. These findings indicate that AtNRAMP6 plays an important role in the growth of Arabidopsis in Fe-deficient conditions.

Vacuolar storage of iron (Fe) is important for Fe homeostasis in plants. When sufficient, excess Fe could be stored in vacuoles for remobilization in the case of Fe deficiency. Although the mechanism of Fe remobilization from vacuoles is critical for crop development under low Fe stress, the transporters that mediate vacuolar Fe translocation into the cytosol in rice remains unknown. Here, we showed that under high Fe²⁺ concentrations, the Δccc1 yeast mutant transformed with the rice natural resistance-associated macrophage protein 2 gene (OsNRAMP2) became more sensitive to Fe toxicity. In rice protoplasts and transgenic plants expressing Pro35S:OsNRAMP2-GFP, OsNRAMP2 was localized to the tonoplast. Vacuolar Fe content in osnramp2 knockdown lines was higher than in the wild type, while the growth of osnramp2 knockdown plants was significantly influenced by Fe deficiency. Furthermore, the germination of osnramp2 knockdown plants was arrested. Conversely, the vacuolar Fe content of Pro35S:OsNRAMP2-GFP lines was significantly lower than in the wild type, and overexpression of OsNRAMP2 increased shoot biomass under Fe deficiency. Taken together, we propose that OsNRAMP2 transports Fe from the vacuole to the cytosol and plays a pivotal role in seed germination.