The development and growth of the plant in general is controlled by nitrogen that is one of the important nutrients. It is understood that iron plays a crucial part in managing the assimilation of nitrate in the presence of enzymes involved in reductive assimilatory pathway. As the information regarding the association of iron deficiency with the nitrogen metabolism in dicots and non-graminaceous monocots was available very little, a study was conducted in cucumber where the nitrogen metabolism was found to be affected by deficiency in iron. Nitrogen is considered as important nutrient beneficial for plants as it is present in nucleotides, chlorophyll, cellular constituents and proteins, according to Marschner, H in his article Mineral nutrition of higher plants. Nitrate ions are considered as abundant nutrients available in the aerobic soil and they are consumed from the soil by the plant through the cortical cells and epidermal cells of the root with the help of inducible high affinity transport system; according to Forde, B in Nitrate transporter in plants: structure, function and regulation article and Miller, A J et al. in the article nitrate transport and signalling.
The enzymes of reductive assimilatory pathway like glutamate synthase, nitrate reductase, and nitrite reductase need iron, iron-heme group or iron-sulphur cluster that can regulate the nitrate ion assimilation according to Marschner, H in his article Mineral nutrition of higher plants. It is understood that the deficiency of iron in the soil will generate certain responses in the root level which enhances the iron ion availability in the rhizosphere. The deficiency of iron in the soil is responded by the strategy I plants (dicots and non-graminaceous monocots). The responses of these plants are the increase in iron ion reduction capacity of the root, enhanced acidification of the rhizosphere to increase the solubility of iron ion and increase in uptake of rhizodermal root cells; according to Curie, C et al. in iron transport and signalling, Kim, S A et al. in Iron uptake and Transport in plants and Abadia, J et al. in towards a knowledge-based correction of iron chlorosis. It is found that the factors that are helpful in the uptake of Fe is managed by many of helix-loop-helix transcriptional factors, FER-like iron deficiency induced transcription factor and PYE.
The uptake of nitrate ion was found to be reduced in the cucumber plants that have Fe deficiency according to Agnolon, F et al. in enzymatic response of cucumber roots to different levels of Fe supply. It is understood that the relation between Fe deficiency and nitrate ion uptake is probably due to two reasons. One of them is that the reduction of equivalent substances are carried out by both nitrate assimilation and Fe uptake. The second one is that the reduction of nitrate ion is carried out by enzymes that consisted of Fe. There is also another possible reason that deficiency of Fe might change the cytosolic levels of nitrate ion resulting in the prevention of uptake process.
The current study focuses on the alteration in the nitrogen metabolism due to the deficiency of Fe in the level of leaves and roots. Fe deficiency was induced in the cucumber plants where the reduction in the nitrate reductase (NR) enzyme activity levels was observed both in the root as well as in the leaf as the induction of Fe deficiency continued. Nitrate reductase is the primary enzyme in the nitrate ion assimilatory pathway. The NR activity levels diminished extensively in leaves than in roots after 7 days. Therefore, the NR activity was affected more in leaves than in roots of cucumber.
The levels of the cytosolic enzyme isocitrate dehydrogenase was found to be higher in the leaves and roots of cucumber seven days after the induction of Fe deficiency. This increase was detected using northern blot analysis of the transcripts of the enzyme. The increase in the cytosolic enzyme glutamate synthase activity was observed as higher in the roots than in the leaves of cucumber plants. The activities of alanine aminotransferase and aspartate aminotransferase were found to be higher in roots of cucumber plants than in the leaves of these plants.
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