Metabolism of 2′-carboxyarabinitol in leaves

Abstract

Results presented here indicate that 2′-carboxyarabinitol (CA) is the in vivo precursor and product of 2′-carboxyarabinitol 1-phosphate (CA1P) metabolism in leaves. When [2-14C]CA was fed in the light to leaves of five species known to be highly active in CA1P metabolism (Phaseolus vulgaris, Lycopersicon esculentum, Helianthus annuus, Petunia hybrida, and Beta vulgaris), [14C]CA1P was formed in the dark. Reillumination of a Phaseolus leaf caused this [14C]CA1P to be rapidly metabolized to [14C]CA (t1/2 = 1 min). The epimer 2′-carboxyribitol could not substitute for CA in the dark synthesis of CA1P, and CA in the anionic form was a better substrate than CA in the lactone form. In leaves of Phaseolus vulgaris, the active CA pool size used in the dark synthesis of CA1 P is between about 70 and 110 nanomoles per milligram of chlorophyll. The photosynthetic electron transport inhibitor diuron did not affect the dark synthesis of [14C]CA1P, but did greatly reduce the rate of its subsequent light degradation (t1/2 -approximately 10 min). Dark synthesis of [14C]CA1P was inhibited by dithiothreitol and NaF. From the present data, we suggest that CA1P and CA participate in a metabolic substrate cycle in vivo.