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

Abstract

SummaryTransgenic 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 À ) experienced 30±70% declines in growth under the same conditions. ATP levels and ATP/ADP ratios for Hb lines did not signi®cantly differ in 40 and 3% oxygen, whereas the ATP levels and ATP/ADP ratios in control and Hb À lines were signi®cantly 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 À line was 2.5-fold higher than that in the Hb line. Treatment of transgenic root lines under 40% oxygen with NO resulted in signi®cant declines in the ATP levels and ATP/ADP ratio of an Hb À line and the control line, with no signi®cant change in an Hb line. The root cell structure of an Hb À 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.

A review of soil NO transformation: Associated processes and possible physiological significance on organisms

“…Hanson, P. J., Lindberg, S. E., 1991 Horchani, F., Prevot, M., Boscari, A., Evangelisti, E., Meilhoc, E., 2251 Bruand, C., Raymond, P., Boncompagni, E., Aschi-Smiti, S., Puppo, A., …”

Nitrogen metabolism in plants under low oxygen stress

“…NO was shown to interact with Hb from different plant species in a Hb/NO cycle, in which the excess NAD(P)H is oxidized for the conversion of NO into nitrate (Hebelstrup et al 2012;Besson-Bard et al 2008b). When alfalfa plants overexpressing Hb were compared to wild type or to Hb-antisense plants, symptoms of hypoxia were improved, leading to a longer survival of the Hb overexpressors (Dordas et al 2003a). NO emission Igamberdiev et al ( , 2010 and Stoimenova et al (2007) was 2.5-fold higher in Hb-silenced plants compared to Hb overexpressors, suggesting that in plants, Hb is involved in the response to hypoxia through the modulation of NO emission and the loss of N to the atmosphere (Dordas et al 2003a).…”

“…When alfalfa plants overexpressing Hb were compared to wild type or to Hb-antisense plants, symptoms of hypoxia were improved, leading to a longer survival of the Hb overexpressors (Dordas et al 2003a). NO emission Igamberdiev et al ( , 2010 and Stoimenova et al (2007) was 2.5-fold higher in Hb-silenced plants compared to Hb overexpressors, suggesting that in plants, Hb is involved in the response to hypoxia through the modulation of NO emission and the loss of N to the atmosphere (Dordas et al 2003a). Thus, an additional positive effect of Hb/NO cycle could be to limit N loss under NO emission when oxygen concentration in the medium is close to anoxia (below 0.1 % O 2 ) (Hebelstrup et al 2012).…”

Vitreoscilla Hemoglobin (VHb) Overexpression Increases Hypoxia Tolerance in Zebrafish (Danio rerio)

“…Capitata), alfalfa (Medicago sativa cv. Regen SY), and petunias, overexpressing VHb can enhance the growth and survival of the plant under hypoxia stress (Dordas et al 2003;Mao et al 2003;Li et al 2005). In microbes, attempts have been made to overcome the problem of limiting oxygen by metabolically engineering bacteria to express the vhb transgene under hypoxic conditions (Patel et al 2000;Nasr et al 2001;So et al 2004;Urgun-Demirtas et al 2004).…”