1004 the Dual Role of Mannitol as Osmoprotectant and Photoassimilate in Celery

Abstract

<jats:p>Mannitol, a six carbon sugar alcohol, is widely distributed in nature and is a major phloem-translocated photoassimilate in celery. II may also function as a compatible osmolyte providing stress tolerance. Until recently, little was known about the route of mannitol catabolism in sink tissues of higher plants. An enzyme. mannitol dehydrogenase. (MDH) that oxidizes mannitol to mannose utilizing NAD as the electron acceptor was discovered (Arch. Biochem. Biophys. 1991. 298:612-619) in “sink” tissues of celery and celeriac plants. The activity of the enzyme is inversely related to tissue mannitol concentration in various parts of celery plants suggesting a role for the enzyme in mannitol catabolism. In osmostressed celery plants, the activity of the enzyme in sink tissues decreases as mannitol accumulates.</jats:p> <jats:p>Celery cells growing heterotrophically in suspension culture utilize either sucrose or mannitol as the sole carbon source and grow equally well on either carbohydrate. Mannitol-grown cells contain more MDI-I activity than sucrose-grown cells, and the activity of the enzyme is correlated with the rate of depletion of mannitol from the culture medium. Cells growing on mannitol contain an internal pool of mannitol but little sugar. Cells growing on sucrose contain internal sugar pools but no mannitol. Mannitol-grown cells are also more salt tolerant than cells grown on sucrose. Our laboratory is involved in studies of the physiological role of the mannitol oxidizing enzyme in regulating mannitol utilization and the role of the enzyme in regulating mannitol pool size during salt and osmostress in both celery plants and celery suspension cultures. Current studies on the molecular control of expression of the enzyme will be discussed.</jats:p>

Influence of soil moisture level on metabolism of non-structural carbohydrates in Quercus robur leaves

“…The action of these strong oxidants can be neutralized by metabolites involved in the process of controlling free radicals (Sudachkova et al, 2015). It has been established that sugars, along with other compounds, protect cells from free radical oxidation (Averyanov & Lapikova, 1989;Pharr, 1995;Couee et al, 2006;Kolupaev & Karpets, 2010). Therefore, given all these protective functions of sugars, increase in their level in leaves of Q. robur in conditions of significant lack of moisture in the soil (in mesoxerophilic and xerophilic forest growth conditions) plays an important role in adapting plants to these growing conditions, increasing their resistance to drought.…”