SOME RELATIONSHIPS BETWEEN THE GAS-EXCHANGE, BIOCHEMISTRY AND MOLECULAR-BIOLOGY OF PHOTOSYNTHESIS DURING LEAF DEVELOPMENT OF TOMATO PLANTS AFTER TRANSFER TO DIFFERENT CARBON-DIOXIDE CONCENTRATIONS

Tomato plants were exposed to four concentrations of CO2 (350, 700, 10 50 or 1400 mu mol CO2 mol(-1)) for 31 d. The light-saturated rate of p hotosynthesis (A) of the unshaded fifth leaf was measured at either an ambient CO2 concentration of 350 mu mol CO2 mol(-1) [A (350)] or at t he level of CO2 at which the plants were grown. The chloroplast protei n composition and the level of transcripts of nuclear or plastid photo synthesis-associated genes (PAGs), as well as the main carbohydrate co ntent of the fifth leaf maintained horizontal and unshaded, were also measured during leaf development. At 60 and 95 % leaf expansion, the A of high CO2-grown plants measured at growth CO2 was higher than the A (350) of the plants grown at ambient CO2. However, in the fully matur e leaves, A (growth CO2) declined linearly as growth CO2 concentration increased. The A (350) of plants exposed to elevated CO2 up to 60% le af expanion had not acclimated to high CO2. At 95% leaf expansion, A ( 350) was lower in plants grown at high CO2. A versus CO2 (C-i) for mat ure leaves showed that A of the plants grown at high CO2 was lower ove r the entire range than that for plants grown at present ambient CO2 c oncentration. Lines fitted to the linear part of the A/C-l curves were concurrent at a C-i of 49 mu mol CO2 mol(-1) and A=-1.21 mu mol CO2 m (-2)s(-1). This C-i value is close to Gamma (46 mu mol CO2 mol(-1)), the compensation point at 27 degrees C calculated from the equation de scribed in Brooks & Farquhar (1985, Planta 165, 397-406). This A is an estimate of respiration in the light (R(1)) and was not affected by a cclimation to elevated CO2. Thylakoid proteins (photosystem I core pro tein, D-1 and D-2 of the photosystem II core complex, cytochrome f) we re all reduced by elevated CO2 only in the fully mature leaves (310 ex posure), whereas the large and small subunits of Rubisco and Rubisco a ctivase proteins had already declined after 22 d exposure. Transcript levels of the plastid-encoded FAG (rbcL, psbA, psaA-B) were reduced in the mature leaves by elevated CO2 when expressed on a total RNA basis , but they were not sensitive to elevated CO2 when expressed on a chlo roplast 16S rRNA basis. However, rbcS, rca and cab mRNA transcripts we re lower in the plants grown at high CO2 than in control plants after 22 d exposure when expressed on a nuclear rRNA basis. The loss of thes e nuclear PAGs was correlated with an accumulation of soluble sugars a nd starch.