Molecular Studies of
I am interested in molecular responses of plants to
abiotic stress, i.e., stress associated with the physical environment.
Current research is focused on hypoxic stress and abscisic acid (
Our hypoxic stress research began with the discovery that hemoglobins, normally associated with mammals, were ubiquitous in plants. These hemoglobins are unique in that they bind oxygen very tightly, resulting in their being oxygenated at very low oxygen concentrations. One of these hemoglobin genes was activated in plant tissues exposed to hypoxic conditions. In the course of our research to relate hemoglobin expression with metabolism during hypoxia, we found that nitric oxide (NO) production increased substantially in hypoxic plant tissue. The amount of measurable NO varied inversely with the hemoglobin levels in the hypoxic tissue. This lead us to experimentally establish the existence of a hemoglobin/NO cycle (see figure) in hypoxic plant tissue. The pathway cycles nitrate through nitrite, NO and back to nitrate with consumption of NAD(P). The NO to nitrate conversion uses oxygenated hemoglobin forming oxidized hemoglobin (methemoglobin), which is reduced back to hemoglobin by NAD(P)H. Since the redox state in the cell environment can become highly reductive during hypoxia, the cycle should result in the cell being having a higher oxidative state when the cycle is operative. This is observed experimentally in cells with varying expression of hemoglobin. Cells expressing hemoglobin during hypoxia maintain their energy status better than cells not expressing the gene. We think we have an explanation for this. We have found that root mitochondria can synthesize ATP under strictly anaerobic conditions using nitrite and NAD(P)H. NO is one of the products of the reaction. We believe that the hemoglobin serves two functions during this process: maintaining anaerobic conditions in the cell by its ability to scavenge oxygen at very low oxygen concentrations, and; reacting with NO, to remove a potentially toxic product, regenerating nitrate for the next round of the cycle. Our work continues to relate these events to other processes in the hypoxic cell.
Igamberdiev AU, Hill RD (2009) Plant mitochondrial function during anaerobiosis. Ann Bot 103: 259-268.
M, Igamberdiev AU, Gupta KJ,
AU, Baron KN,
Igamberdiev AU, Stoimenova M, Seregélyes C, Hill RD (2006) Class-1 hemoglobin and antioxidant metabolism in alfalfa roots. Planta 233: 1041-1046 [pdf]
Guy PA, Duff SMG, Nie X,
Igamberdiev AU, Baron K, Manac'h-Little N, Stoimenova M, Hill RD (2005) The haemoglobin/nitric oxide cycle: Involvement in flooding stress and effects on hormone signalling. Ann Bot 96: 557-564 [pdf]
Manac'h-Little N., Igamberdiev AU,
Igamberdiev AU and
Seregélyes C, Igamberdiev AU, Maassen A, Hennig A, Dudits D, Hill RD (2004) NO-degradation by alfalfa class 1 hemoglobin (Mhb1): a possible link to PR-1a gene expression in Mhb1-overproducing tobacco plants. FEBS Letters 571: 61-66 [pdf]
Dordas C, Hasinoff BB, Rivoal J,
Igamberdiev AU, Seregélyes C, Manac'h N,
Dordas C, Hasinoff BB, Igamberdiev AU, Manac’h N, Rivoal J,