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Mechanism of photosynthate efflux from Vicia faba L. seed coats



Mechanism of photosynthate efflux from Vicia faba L. seed coats



Journal of Experimental Botany 44(258): 65-74



In order to develop a tentative model of the mechanism of photosynthate efflux from the vascular region of Vicia faba L. seed coats, wash-out experiments were performed after removal of the embryo. The sulphydryl group modifiers, pCMBS and NEM, reduced 14C-photosynthate efflux by 40% and 50%. respectively. Their inhibitory effect could be prevented or reduced (in the latter case) by including DTT in the bathing solution. Maltose competed with sucrose for efflux; a concentration of 300 mol m-3 inhibited 14C-photosynthate release by 35%. The cations K+, Na+', Mg-2+, and TPP+ enhanced efflux significantly, whereas the counterion Cl- had no effect. The presence of the protonophore CCCP (0.1 mol m-3) led to a reduction of efflux by 50%: net proton extrusion dropped by 34%. To a lesser extent, an efflux inhibition was also achieved by decreasing the cytoplasmic pH with the weak acid DMO. In contrast, alterations in the external pH caused only a feeble response. The ATPase inhibitor, EB, decreased photosynthate efflux and H+ extrusion. DES reduced efflux slightly, presumably by affecting ATPase activity as well as energy metabolism. Based on these findings, it is proposed that a sucrose/proton antiport mechanism could be responsible for photosynthate efflux from Vicia faba seed coats.

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Accession: 009002919

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DOI: 10.1093/jxb/44.1.65


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