| Fe is an essential nutrient element for plants. It is vital for a variety of cellular and other physiological functions ranging from metabolism, to growth and development, including chlorophyll synthesis, respiration, redox reactions and electron transfer. Although Fe is one of the most abundant elements in the geosphere, many plants suffer from Fe deficiency. This deficiency is attributed to the fact that Fe in soil exists mostly as Fe-oxides, phosphate or other insoluble compounds. Thus iron deficiency is a major abiotic stress limiting plant growth rates and crop yield. Low accumulation of iron in edible portions of plants also poses negative nutritional problems for humans and animals. Rice is a main crop in the world, nearly two thirds of the world’s population feeds on rice. Therefore, how to acquire iron accumulation in rice has become a popular research field. In this study, we used H 9405, a cultivar of rice with high Fe accumulation in seeds, and Yang 6, a cultivar with low seed Fe accumulation, to study their responses under different Fe conditions. Rice genotypes differing in seed iron accumulation and tolerance to Fe deficiency have not been tested yet. In this study, special attention was paid to rice growth status, photosynthetic characteristics, anti-oxidation systems and both marker genes correlated with Fe uptake and transport and changes in protein levels. Our research aimed at understanding how plants adapt to changes in Fe supply and the different response mechanisms in different genotypes at the molecular and physiological levels. Our experimental data indicate that differential root uptake and shoot remobilization occurs, and a signal component transmitted from shoot to root may be responsible for the differential Fe status in the two cultivars. The main results were as follows:1. Rice growth and development status was affected by supplied iron form within different genotypesAs rice has two iron uptake strategies, we investigated the growth and development status of Yang 6 and H 9405 using different forms of iron. We measured the iron distribution characteristics, chlorophyll content and leaf and root cell ultrastructure. H 9405 behaved well with all forms of iron, while for Yang 6, the iron content and chlorophyll content were significantly decreased when fed only Fe2+, and also the leaf and root ultrastructure were damaged.2. Differential regulation of proteins in rice under iron deficiencyTo investigate the adaptive mechanism of a Chinese rice variety grown under iron deficiency, proteins differentially accumulated in leaves and roots of Yang 6, an indica cultivar, under Fe deficiency growth condition, were profiled using a two-dimensional electrophoresis (2-DE) and Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry(MALDI-TOF/MS). The accumulations of seventy three proteins were detected to be increased or decreased upon iron deficiency, and sixty three of them were successfully identified. Among the sixty three proteins, a total of forty proteins were identified in rice leaves, and twenty three proteins were in roots. Most of these proteins are involved in photosynthesis, carbohydrate metabolism, oxidative stress, Adenosine triphosphate (ATP) synthesis, cell growth or signal transduction. The results provide a comprehensive way to understand, at the level of proteins, the adaptive mechanism used by rice shoots and roots under iron deficiency. Based on the discovery from the proteomic information under iron deficiency, special attention was paid to rice growth status, photosynthetic characteristics, anti-oxidation systems and both marker genes correlated with Fe uptake and transport and signal transduction in the later research.3. Iron deficiency can inhibit the growth and iron distribution within two rice genotypesIn this study, Yang 6 and H 9405 were used to investigate their growth status and iron distribution response under iron deficiency. Our results showed iron deficiency, with lower Fe content in both shoots and roots, could inhibit both the length and dry weight of shoots and roots in the two varieties. Furthermore, we found the distribution of iron in the whole plant of Yang 6 and H 9405 also differs. In H 9405, the most part of iron accumulated in its shoot, while in Yang 6, it is in the root. It suggests that the variety with more iron in seeds may have a stronger ability to transport iron from root to shoot.4. Effects of iron deficiency on anti-oxidative system and photosynthetic system within two rice genotypesUnder iron deficiency, H 9405 and Yang 6 showed different response in the anti-oxidative system. We measured some marker enzymes involved in the detoxification of dangerous forms of oxygen, and regeneration of reducing agents, within the two varieties in both shoots and roots. Our results showed in H 9405, the leafs anti-oxidative enzymes showed no changes, while in root, they were activated. In Yang 6, the detoxification cycle was activated in both shoots and roots.Iron functions in the biosynthesis of chlorophyll, and many enzymes involved in the photosynthetic system contain iron. Therefore, iron deficiency can affect the photosynthesis and respiration process. We measured the chlorophyll content, photosynthetic rate, mesophyll cell and root tip cell ultrastructure under iron deficiency. Under iron deficiency, the chlorophyll content was dramatically decreased in Yang 6, while in H 9405 the decrease was much lower. Yang 6 also showed a significant decrease in photosynthetic rate under iron deficiency while H 9405 showed no change. Also, damage to leaf and root ultrastructure under iron deficiency was much greater in Yang 6 than in H 9405.5. Iron deficiency can induce iron uptake and transport genes within two rice genotypes and the existing proof of long distance signaling generated in shootUnder Fe deficiency conditions, plants alter a number of processes in order to acquire Fe from soil. Genes involved in these mechanisms have been identified from different model plants, including Arabidopsis and rice. Fe transport within plants is also tightly regulated. We found that genes involved in acquisition of Fe from soil in these two cultivars were both up-regulated in roots under Fe deficiency condition, and the elevation of the expression was much higher in Yang 6 than in H9405. However, remobilization related genes in the shoot vasculature were expressed in an opposite way between the two cultivars. In H9405, the expression of these genes was up-regulated; but in Yang 6, their expression was reduced. Strategies to biofortify rice cultivars with different characteristics were also discussed based on our discovery.Long-distance feedback signaling coordinate plays a key role in nutrient uptake of botany. There exists a tight relationship between signal generated by the shoot and the ability of nutrient uptake of the root. At present, the mechanism of the long-distance signal is still under revelation. As mentioned in the previous chapters, we hypothesis the long-distance signal exists in rice under iron deficiency can coordinate the whole plants’ physiological metabolism. In order to clarify the hypothesis, we used the shoot exicision experiment to demonstrate exist of the signal. Based on the results, we can conclude the signal generated in the shoot can transfer to regulate the iron uptake marker gene in root in nee. |
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