Plant nutritional status modulates glutamine synthetase level in Micro-Tom ripe fruit

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

JOURNAL OF PLANT PHYSIOLOGY

ELSEVIER

Año: 2006 p. 1 - 1

0176-1617

Tomato (Solanum lycopersicum) fruit ripening implies a complex recycling program in which chloroplastic proteins are degraded and new proteins are synthesized. Supplementary nutrition is frequently required when Micro-Tom plants begin to fruit and continues until the end of the plant life cycle. Ammonium assimilation is crucial in these fruit maturation and ripening processes. Glutamine synthetase (GS; EC 6.3.1.2), the main ammonium-fixing enzyme in plants, could not be detected in red fruits of several tomato varieties when growing under standard nutrition.  In this paper we analyze the influence of nutritional status in the ammonium assimilation capacity of ripe tomato (cv. Micro-Tom) fruit.   For this purpose, GS expression and protein profiles were followed in mature green and red fruits harvested from plants grown under standard or high nutrition. Under standard nutrient regime (Micro-Tom plants weekly supplied with 0.5x Hoagland solution) GS was quite active in the chloroplasts (GS2) of mature green fruits, and it was not detected either in the chromoplast or in the cytosol of red fruit. When plants were shifted to high nutritional condition (daily irrigated with 0.5x Hoagland solution), GS protein was clearly observed in red fruits. Also, cytosolic (gs1) transcripts preferentially accumulated in red fruits under high nutrition. These results indicate that mature Micro-Tom fruits assimilate ammonia through GS2 in green fruit under standard nutrition, while ripe fruit responds to high nutrition accumulating GS1, in order to assimilate the extra N-compounds provided by the vascular system.