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内容記述 |
[Introduction] Iron (Fe) is an essential element for plants and is particularly indispensable for the functioning of the photosystem in chloroplasts. Fe deficiency perturbs the photosystem I (PSI) function since it requires a large amount of Fe and thus generates photo-oxidative stress. The barley cultivar “Sarab 1” exhibits extremely high tolerance to Fe deficiency, which is associated with PSI maintenance with high photosynthetic Fe-use efficiency during Fe deficiency. However, how “Sarab 1” maintains PSI function has not been clarified. [Aim of this study] This study explores the mechanisms associated with maintaining PSI in “Sarab 1” during Fe deficiency. [Methods] Barley cultivars (Hordeum vulgare L.) with different Fe deficiency tolerances were grown hydroponically with 30 μM Fe for control plants and 0.5-3 μM for Fe-deficient plants, respectively. A live autography system consisting of a high-sensitivity CCD camera and a fluorescent plate with a phosphor layer was used for analyzing 59Fe influx rates. The function of the photosystem was determined by Dual-PAM-100 and LI-6800F. [Results] The live autography to monitor the 59Fe influx revealed that “Sarab1” had the lowest rate of Fe absorption during Fe deficiency compared to the other cultivars with lower Fe deficiency tolerance. Consistent with the low Fe absorption, the amount of PSI was significantly decreased in Fe-deficient “Sarab 1.” Nevertheless, the electron transfer rate of the remaining PSI of Fe-deficient “Sarab 1” was as high as that of the control leaves. Electron microscopy analysis revealed that “Sarab 1” had more non-stacked stroma lamellae in thylakoid membranes than other cultivars we investigated. Predicting that this membrane organization of “Sarab 1” is associated with maintaining PSI function, we isolated the stroma lamellae-enriched lower-density thylakoid (L-Thy) membrane. We found that “Sarab 1” had a higher allocation of the light-harvesting antenna Lhcb1 into L- Thy than other cultivars. Furthermore, higher amounts of Fe-binding proteins were detected in the thylakoid membrane of “Sarab 1.” [Discussion] “Sarab 1” acclimates to Fe deficiency by maintaining a small amount of but high- performance PSI. We assumed that the abundant Lhcb1 on the L-Thy of “Sarab 1” plays a role in avoiding photodamage in PSI since Lhcb1 in barley has a significant role in the photoprotective thermal dissipation during Fe deficiency, as we have reported. In addition to such a photoprotective mechanism, some Fe-binding proteins could allow "Sarab 1" to maintain PSI integrity and promote the efficient turnover of damaged PSI. |
