Effects of light and atmospheric carbon dioxide enrichment on photosynthesis and carbon partitioning in the leaves of tomato (Lycopersicon esculentum L.) plants over-expressing sucrose phosphate synthase

Abstract

Photosynthetic carbon assimilation, carbon partitioning and foliar carbon budgets were measured in the leaves of transformed tomato plants expressing a maize sucrose-phosphate synthase (SPS) gene in addition to the native enzyme, and in untransformed controls. The maize SPS gene was expressed under control of either the promoter of the small subunit of ribulose 1,5-bisphosphate carboxylase (rbcS promoter; lines 2, 9 and 18) or the 35S promoter from cauliflower mosaic virus (CaMV promoter; line 13). The rate of sucrose synthesis was increased relative to that of starch and sucrose/starch ratios were higher throughout the photoperiod in the leaves of all plants expressing high SPS activity. The leaf carbon budget over the day/night cycle in air at low irradiance (180μmol photon m−2 s−1) was similar in all plants. Net photosynthesis measured in air and at elevated CO2 (800–1500 μl l−1) on whole plants grown in air at 400μmol m−2 s−1 irradiance was significantly increased in the high SPS expressors compared to the untransformed controls and was highest where SPS activity was greatest. At high CO2 the stimulation of photosynthesis was more pronounced. We conclude that SPS activity is a major point of control of photosynthesis particularly under saturating light and CO2.

Developmental regulation of photosynthate distribution in leaves of rice

“…Galtier et al (1993) demonstrated a positive relationship between SPS activity and the sucrose/starch ratio by changing the level of SPS in tomato transformed with a maize SPS gene, resulting in increased starch degradation in the chloroplasts. Similar effects were reported by Galtier et al (1995) and Micallef et al (1995). Thus, once dihydroxyacetone phosphate (DHAP) is released from the chloroplast, the rate of sucrose synthesis is regulated by SPS activity.…”

Changes in Photosynthetic Activity and Export of Carbon by Overexpressing a Maize Sucrose-Phosphate Synthase Gene under Elevated C02in Transgenic Rice

“…In transgenic tomato overexpressing a maize SPS gene and wild-type tomato under ambient [C0 2 ], no significant difference was observed in estimated carbohydrate export from the source leaves (Galtier et al, 1995), and under elevated [C0 2 ], the export rate was only slightly (5%) higher in transgenic tomato (Murchie et al, Galtier et al, 1995;Murchie et al, 1999). In tomato, starch might accumulate to a level that exceeds the demand, and other regulatory mechanisms, such as activity of the sucrose transporter, might counteract the advantage of the high SPS activity under elevated [C0 2 ], as mentioned by Murchie et al (1999).…”

Cassava brown streak disease effects on leaf metabolites and pigment accumulation

“…Leaf samples were Lyophilised in a freeze dryer (Labconco Freezone18). The freeze dried leaf materials (5 g) were homogenised in 1M HClO 4 (25 ml), and the extract was centrifuged at 12,000 g for 5 min at 4 o C (Galtier et al, 1995).…”