PARENT SESSION
Posters P4B Sugar signalling: Photosynthesis, hormones and development. Abstracts (480-527)

Diel patterns of leaf ¹⁴C-export and of main and lateral shoot growth for Flaveria linearis with altered leaf sucrose-starch partitioning. Evangelos Leonardos^*,1, Barry Micallef¹, Malgre Micallef¹, Bernard Grodzinski^*,1, ¹ Department of Plant Agriculture, Guelph, ON, Canada

ABSTRACT- Leaf photosynthesis and ¹⁴C-export in two parental F. linearis lines [85-1: high activity of cytosolic Fructose-1,6-bisphosphatase (cytFBPase) and 84-9: low activity of cytFBPase] were estimated using steady-state ¹⁴CO₂ labelling. Using these lines and an F₂ population segregating for cytFBPase activity (high, intermediate, low), the proportion of recently fixed C incorporated into starch was quantified, the growth rates over time of main and lateral branches were determined non-destructively, and diel patterns of main and lateral stem growth were quantified using linear voltage signal transducers. A higher proportion of ¹⁴C was incorporated into starch rather than sucrose in 84-9. Photosynthesis and ¹⁴C-export during daytime were higher in 85-1. Relative ¹⁴C-export (% of photosynthesis) was about 40% higher in 85-1. ¹⁴C-export were higher at the beginning of the night in 84-9, but similar in the two lines at the end of the night. At night, about 25% more ¹⁴C was exported and 44% more ¹⁴C was respired in 84-9. More ¹⁴C remained in the leaves of 84-9 both at the end of day and end of night. The diel export patterns obtained using ¹⁴CO₂ correlated with estimates based on measurements of assimilate fluxes through leaf C-pools during the daytime, but not during the night. In the F₂ population, a strong correlation was found between % recently fixed C incorporated into starch, the rates of main and lateral branch growth, and diel patterns of main and lateral branch growth. The main stem growth rate was up to 40% lower in lines partitioning a greater % of recently fixed C into starch, and there was a concomitant increase in the lateral branch growth rate. In conclusion, a change in sucrose-starch partitioning can alter the diel patterns of export from the leaf that can influence the patterns of main and lateral branch growth in F. linearis.

KEY WORDS: carbon export, diel patterns, Flaveria linearis, carbon partitioning