We have shown that the photosynthetic period is important in regulating carbon partitioning. Even when the same amount of carbon is fixed over a 24h period considerably more is translocated out of the leaf under the longer photosynthetic period. This is extremely important when parts of the plant other than the leaves are to be sold. It is also important to notice the amount of carbon respired in the short photosynthetic period. The light period effect on carbohydrate fixation, dark respiration and translocation is shown in the following table.


Length of light period (h)

Photosyn    rate             (g CH2O m-2 h-1) Total CH2O fixed during light period

(g m-2)

Total CH2O respired during dark period

(g m-2)

Total CH2O translocated during light period

(g m-2)

Total CH2O translocated over 25 h

(g m-2)

8 0.74b 5.95a 1.56b 1.29b 3.46a
16 0.37a 5.87a 0.55a 3.32a 4.88b

Note: Values in column followed by the same letter are not significantly different at P£ 0.05 using F-test.

Experimental Conditions:

  • Incandescent and cool white flourescent lamps (plants were grown for 38 days under 12 hr photoperiod at 150 µmol m-2s-1. At 38 days the plants were separated into 2 groups. One group received an 8 hr photoperiod at 300 µmol m-2s-1 and a second group received a 16 hr photoperiod at 150 µmol m-2s-1)
  • Temperature: Day = 26o C Night = 23o C
  • Humidity: 70-80%
  • CO2: 350-400 ppm
  • Plants were grown in 10 cm pots in a peat: vermiculite: perlite mix (40:40:20 by volume)
  • Plants were irrigated twice weekly with half-strength Hoagland solution


Lobendra, S. & H.W. Janes, 1992. Light Duration Effects on Carbon Partitioning     and Translocation in Tomato. Scientia Horticultura 52: 19-25.


Janes, H.W. 1994.Light period regulation of carbohydrate partitioning, p 51. In: T.W.Tibbitts (ed.). International Lighting in Controlled Environments Workshop, NASA-CP-95-3309.

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