Bifunctional enzyme which has both carbonate dehydratase and monodehydroascorbate reductase activities. May be involved in regulation of nectar pH. May also regulate nectar ascorbate concentration, protecting floral tissues from free radical damage. H(+) + 2 monodehydro-L-ascorbate radical + NADH = 2 L-ascorbate + NAD(+) H(+) + hydrogencarbonate = CO2 + H2O Found in the nectar. Expressed most strongly in nectary gland. Also at lower levels in the ovary, style, stigma, floral tube and at low levels in anthers/filaments. Expressed at low levels in stage 2 nectaries. Levels then increase and expression is even throughout subsequent stages of nectary development. Proteolytically cleaved to produce a shorter protein, nectarin-2. Belongs to the alpha-carbonic anhydrase family.