Plant nutritional status modulates glutamine synthetase levels in ripe tomatoes (Solanum lycopersicum cv. Micro-Tom)

SCARPECI TE, MARRO ML, BORTOLOTTI S, BOGGIO SB, VALLE EM

JOURNAL OF PLANT PHYSIOLOGY

Elsevier

Año: 2007 vol. 164 p. 137 - 145

0176-1617

Tomato (Solanum lycopersicum) fruit ripening implies that chloroplastic proteins aredegraded and new proteins are synthesized. Supplementary nutrition is frequentlyrequired when tomato plants begin to fruit and continues until the end of the plant’slife cycle. Ammonium assimilation is crucial in these fruit maturation and ripeningprocesses. Glutamine synthetase (GS; EC 6.3.1.2), the main ammonium-fixing enzymein plants, could not be detected in red fruits of several tomato varieties when growingunder standard nutrition. In this paper, we analyze the influence of the nutritionalstatus on the ammonium assimilation capacity of ripe tomato (cv. Micro-Tom) fruit. Forthis purpose, GS expression and protein profiles were followed in mature green andred fruits harvested from plants grown under standard or supplemented nutrition.Under standard nutrient regime (weekly supplied with 0.5
Hoagland solution) GSactivity was found in chloroplasts (GS2) of mature green fruits, but it was not detectedeither in the chromoplasts or in the cytosol of red fruits. When plants were shifted to asupplemented nutritional regime (daily supplied with 0.5
Hoagland solution), GS wasfound in red fruits. Also, cytosolic (gs1) transcripts preferentially accumulated in redfruits under high nutrition. These results indicate that mature green Micro-Tom fruitsassimilate ammonia through GS2 under standard nutrition, while ripe red fruitsaccumulate GS1 under high nutrition, probably in order to assimilate the extra Ncompoundsmade available through supplemented nutrition.