Five years ago, with international funding, several international agricultural research centers set out to explore the potential to improve the micronutrient quality of some staple food crops Five objectives were identified, and all needed a favorable result if breeding for higher micronutrient density in the staples were to be deemed feasible Useful genetic variation to exploit was needed The traits needed to be manageable in a breeding program (simple screening and high heritability), and stable across a wide range of environments if impact was to be large Above all, the traits needed to be combinable with traits for high yield to ensure that farmers chose the improved lines Finally, it was necessary to show that the new types actually improved the health of humans of low nutrient status representing the target populations The extra nutrients needed to be bioavailable to the gut Today, only this last essential criterion remains to be fully satisfied All other criteria are met to levels that lead us to claim that breeding for nutritional quality is a viable, practicable, and cost-effective strategy to complement existing interventionist strategies Subject to satisfying the last criterion, and results are encouraging, we call for a major funding initiative, and the installation of a new paradigm for 21st century agriculture: one espousing food systems that are highly productive, sustainable, and nutritious This paper reviews the case for and the rationale behind the project that is underway, gives an overview of the results to date and looks at the critical issues that still remain to be confronted

Addressing micronutrient malnutrition through enhancing the nutritional quality of staple foods: Principles, perspectives and knowledge gaps

Plant protoplasts: status and biotechnological perspectives

The role of nitrate reduction to produce nitric oxide (NO) and its subsequent oxidation by oxyhaemoglobin as a mechanism to maintain plant cell energetics during hypoxia is examined. Nitrate reduction in hypoxic conditions can be considered as an alternative respiratory pathway, with nitrate as an intermediate electron acceptor, contributing to the oxidation of NADH. NO, produced in the reaction, does not accumulate due to the induction of hypoxia-induced (class 1) haemoglobins. These haemoglobins remain in the oxyhaemoglobin form, even at oxygen tensions two orders of magnitude lower than necessary to saturate cytochrome c oxidase. They act, probably in conjunction with a flavoprotein, as NO dioxygenases converting NO back to nitrate, consuming NAD(P)H in the process. The overall system oxidizes 2.5 moles of NADH per one mole of nitrate recycled during the reaction, leading to the maintenance of redox and energy status during hypoxia and resulting in the reduced production of ethanol and lactic acid.

/pdf/nitrate-no-and-haemoglobin-in-plant-adaptation-to-hypoxia-an-1wxe6yg9gc.pdf

Nitrate, NO and haemoglobin in plant adaptation to hypoxia: an alternative to classic fermentation pathways

Transgenic alfalfa root cultures expressing sense and antisense barley hemoglobin transcripts were examined under varying levels of atmospheric oxygen. Root cultures overexpressing the hemoglobin gene (Hb+) maintained root growth when placed under 3% oxygen, whereas control cultures or cultures underexpressing hemoglobin (Hb-) experienced 30-70% declines in growth under the same conditions. ATP levels and ATP/ADP ratios for Hb+ lines did not significantly differ in 40 and 3% oxygen, whereas the ATP levels and ATP/ADP ratios in control and Hb- lines were significantly lower under 3% oxygen. Large increases in the production of nitric oxide (NO) were measured in root cultures grown under hypoxic conditions compared to aerobic conditions. The amount of NO accumulated in an Hb- line was 2.5-fold higher than that in the Hb+ line. Treatment of transgenic root lines under 40% oxygen with NO resulted in significant declines in the ATP levels and ATP/ADP ratio of an Hb- line and the control line, with no significant change in an Hb+ line. The root cell structure of an Hb- line showed evidence of cell breakdown under hypoxic growth, whereas an Hb+ line had no evidence of cell breakdown under similar growth conditions. These results lead us to hypothesize that NO is involved in the response of plants to hypoxia and that hemoglobin modulates the levels of NO in the hypoxic cell.

Expression of a stress-induced hemoglobin affects NO levels produced by alfalfa root cultures under hypoxic stress.

How biology handles nitrite.

Although nonsymbiotic hemoglobins (Hbs) are found in different tissues of dicots and monocots, very little is known about hb genes in monocots and the function of Hbs in nonsymbiotic tissues. We report the cloning and analysis of two rice (Oryza sativa L.) hb genes, hb1 and hb2, that code for plant Hbs. Rice hb1 and hb2 genes contain four exons and three introns, as with all of the known plant hb genes. At least three copies of the hb gene were detected in rice DNA, and analysis of gene expression shows that hb1 and hb2 are expressed in leaves but only hb1 is expressed in roots. A cDNA for rice Hb1 was expressed in Escherichia coli, and the recombinant Hb (rHb1) shows an unusually high affinity for O2 because of a very low dissociation constant. The absorbance spectra of the ferric and deoxyferrous rHb1 indicate that, in contrast to symbiotic Hbs, a distal ligand is coordinated to the ligand-binding site. Mutation of the distal His demonstrates that this residue coordinates the heme Fe of ferric and deoxyferrous rHb1 and stabilizes O2 in oxy-rHb1. The biochemical properties of rice rHb1 suggest that this protein probably does not function to facilitate the diffusion of O2.

Rice Hemoglobins (Gene Cloning, Analysis, and O2-Binding Kinetics of a Recombinant Protein Synthesized in Escherichia coli)

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Rice Hemoglobins (Gene Cloning, Analysis, and O2-Binding Kinetics of a Recombinant Protein Synthesized in Escherichia coli)