Short-term feedback inhibition of photosynthesis in wheat leaves supplied with sucrose and glycerol at two temperatures |
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Authors: | R Morcuende P Pérez R Martínez-Carrasco |
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Institution: | (1) Instituto de Recursos Naturales y Agrobiologí a de Salamanca, CSIC, Apartado 257, E-37071 Salamanca, Spain |
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Abstract: | The inhibition of photosynthesis by reduced sink demand or low rates of end product synthesis was investigated by supplying
detached wheat (Triticum aestivum L. cv. Tauro) leaves with 50 mM sucrose, 50 mM glycerol or water through the transpiration stream for 2 h, either at 23 or
12 °C. Lowering the temperature and sucrose and glycerol feeding decreased photosynthetic oxygen evolution at high irradiance
and saturating CO2. The decrease in temperature reduced the pools of sucrose and starch, and the ratio glucose 6-phosphate (G6P)/fructose 6-phosphate
(F6P), while it increased the concentrations of G6P and F6P (hexose phosphates). Sucrose feeding, in contrast to glycerol
feeding, increased sucrose, glucose and fructose contents and the G6P/F6P ratio. Sucrose and glycerol incubations at 23 °C,
as well as decreasing the temperature in leaves incubated in water, increased the concentration of triose-phosphates
(glyceraldehyde 3-phosphate and dihydroxyacetone phosphate, TP) and decreased the glycerate 3-phosphate (PGA) content, thus
increasing the TP/PGA ratio; they also tended to increase the ribulose 1,5-bisphosphate (RuBP) content and the RuBP/PGA ratio.
Sucrose and glycerol feeding at 12 °C and the decrease in temperature of leaves incubated in these solutions decreased TP
and RuBP contents and the TP/PGA and RuBP/PGA ratios. The results suggest that the phosphate limitation caused by accumulation
of end products, restriction of their synthesis and sequestration of cytosolic phosphate can inhibit photosynthesis through
decreased carboxylation of RuBP or, with increased phosphate limitation, through lowered supply of ATP.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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