Non-phosphorylating glyceraldehyde-3P dehydrogenases from leaf and endosperm tissues of wheat exhibit different regulatory and structural properties

A.A. IGLESIAS, D.M. BUSTOS

San Diego, California, USA

Congreso; Annual Meeting of the American Society of Plant Biologists (ASPB); 2000

ASPB

Non-phosphorylating glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.9; abbrev. GAPN) catalyzes the practically irreversible oxidation of glyceraldehyde-3P to 3P-glycerate with the respective reduction of NADP to NADPH. GAPNs from the leaf of a number of plants have been characterized and shown that the enzyme is involved in a shuttle system for the export of NADPH from the chloroplast to the cytosol, via the transfer of triose-P. The enzyme from non-photosynthetic tissues of plants has been less studied respect to properties and functions. We purified GAPN from leaf and endosperm of wheat and made a comparative study concerning the properties of both enzymes. Interestingly, GAPN from endosperm exhibited distinctive regulatory properties, as it was activated by Mg-ATP and inhibited by inorganic pyrophosphate (PPi). GAPN specific activity in leaf extracts was more than 3-fold higher than that observed in endosperm extracts. This is in agreement with different transcript levels evidenced from northern blot experiments using poly(a)+RNA from the respective tissue. Southern blot analysis with genomic DNA revealed the presence of only one gene. RT-PCR studies, using specific primers set for maize GAPN, showed differences in transcript patterns found in each tissue, thus suggesting that the enzymes from leaf and endosperm possess different primary structure. As a whole, results indicate that GAPN from photosynthetic and reserve tissues are differently regulated. It is suggested that the endosperm enzyme play a critical role in carbohydrate and energy partitioning in non-photosynthetic tissues of higher plants.