Mannose inhibits Arabidopsis germination via a hexokinase-mediated step

Low concentrations of the glucose (Glc) analog mannose (Man) inhibit germin ation of Arabidopsis seeds. Man is phosphorylated by hexokinase (HXK), but the absence of germination was not due to ATP or phosphate depletion. The a ddition of metabolizable sugars reversed the Man-mediated inhibition of ger mination. Carbohydrate-mediated regulation of gene expression involving a H XK-mediated pathway is known to be activated by Glc, Man, and other monosac charides. Therefore, we investigated whether Man blocks germination through this system. By testing other Glc analogs, we found that 2-deoxyglucose, w hich, like Man, is phosphorylated by HXK, also blocked germination; no inhi bition was observed with 6-deoxyglucose or 3-O-methylglucose, which are not substrates for HXK. Since these latter two sugars are taken up at a rate s imilar to that of Man, uptake is unlikely to be involved in the inhibition of germination. Furthermore, we show that mannoheptulose, a specific HXK in hibitor, restores germination of seeds grown in the presence of Man. We con clude that HXK is involved in the Man-mediated repression of germination of Arabidopsis seeds, possibly via energy depletion.