Assimilate partitioning in leaves of the raffinose-storing herb Lamium album L.: photosynthesis and carbon partitioning throughout the photoperiod

Lamium album accumulates starch, sucrose and raffinose-family oligosaccharides (RFO) as the major products of photosynthesis. These products were measured in leaves throughout a sixteen-hour photoperiod and under various irradiance conditions. There was continuous accumulation of sucrose and starch. The rate of gas exchange was higher at 500 µEm² s-1 and 900 µEm²s-1 than at 300 µEm² s-1. The rate of photosynthesis did not decline over the sixteen-hour photoperiod, which suggested that there was no short-term feed back inhibition due to sucrose accumulation in this plant. When the products of photosynthesis were compared at the end of the photoperiod, only sucrose increased in abundance at high irradiance. The RFO pool in leaves was shown to contain raffinose, stachyose and verbascose; galactinol was also present. 14CO2 feeding demonstrated that roots and flowers were the major sinks. The middle leaves were major source leaves whilst young leaves acted as both sources and sinks.