LIGHT DURATION EFFECTS ON CARBON PARTITIONING AND TRANSLOCATION IN TOMATO

The influence of light duration on carbon partitioning and translocation in young tomato (Lycopersicon esculentum Mill.) plants growing under similar daily total radiation (DTR) was investigated. The plants were grown under an 8- or 16-h light period with a DTR of 8.64 mol m-2 day-1 for 7 days. The plants grown under both light durations fixed similar amounts of carbohydrate per day. However, the amounts of carbon translocated during the light period and over 24 h were higher in the 16-h light treatment as compared with the 8-h light treatment. The amounts of hexose, sucrose and starch accumulated during the light period and their rates of accumulation were higher in the 8-h than the 16-h light treatment. Thus, even though similar amounts of carbohydrate were fixed by plants in both treatments, more carbon was partitioned into sucrose and translocated out of the leaves in plants grown under 16-h light treatment. These results suggested that carbon partitioning and translocation in the source leaves may be directly affected by light duration or they could be indirectly affected by a light effect on sink activity. These two possibilities are discussed.