containing proteins, capable of supporting reversible binding of oxygen.
They represent a widespread family of proteins found in animals,
plants, fungi and bacteria.
The tertiary structure of these proteins appears to be highly
conserved suggesting commonality of functions.
The basic role of hemoglobins
is closely related to the delivery of oxygen to respiring tissues.
Until recently, the knowledge on plant hemoglobins was limited to the
symbiotic systems in which fixation of free nitrogen occurs (Appleby, 1984).
facilitate the diffusion of oxygen to the bacteroids in the root nodule and
at the same time, by sequestering the oxygen, they prevent the bacterial
nitrogenase from being inactivated.
The discovery of hemoglobins
in cereals (Taylor et al., 1994) and of a nonsymbiotic type
hemoglobin in soybean tissues (Andersson et al., 1996) suggests that
in plants the role of hemoglobins
is not restricted to the nodulation process.