Tomato (Lycopersicon esculentum) plants were grown in liquid culture inside the greenhouse of Hiroshima University, Japan. At the first fruiting stage, P was withdrawn from the rooting medium for a period of 19 d and its effect was studied on photosynthesis, stomatal conductance, transpiration, partitioning of 13C and 15N, P contents of various organs, and changes in stem and fruit diameter of the plant in order to identify the mechanism of resource management on the part of the plant at low P. Compared to the control, P-deficiency treatment decreased biomass growth of all organs except the roots. The treatment also depressed leaf photosynthesis, stomatal conductance and diameter of fruit and stem after a lag period of about 1 week. The stem diameter of the plant shrank during daytime and expanded during the night; the adverse effect of P-deficiency on stem diameter change was more evident during the night than the day. The circadian rhythm in fluctuations of diameter was less manifested in the fruit compared with the stem. P-deficiency induced daytime shrinkage and reduced night expansion of fruit. However, within the plant, P-deficiency encouraged partitioning of 13C, 15N and P into the fruit at the cost of autotrophic organs such as leaves and the upper parts of the stem. The results were discussed in the light of a plausible effect of P-deficiency on water relations of the plant. It is concluded that, in spite of the preference in partitioning of C and N received within the plant parts, assimilate flow into the fruit is limited at low-P compared with the control, owing to the restriction in fruit expansion.

Tomato (Lycopersicon esculentum) plants were grown in hydroponics. At the fruiting stage, N was withdrawn from the growing medium for a period of 19 days and its effects were studied on plant biomass production, photosynthesis, partitioning of 13 C and 15 N, and changes in the stem and fruit diameters etc, in order to monitor the mechanism of resource management on the plant parts at low N and prevent excess use of the fertilizer. N-deficiency treatment decreased leaf photosynthesis immediately and affected biomass accumulation of tomato. Conversely, N-deficiency increased stem diameter for a period of two weeks before reducing it below the control. During this period, these results suggest that N deficiency more suppress source activity than sink activity. N-deficiency reduced the amplitude of the circadian pattern of daytime shrinkage and nocturnal expansion of the stem diameter by decreasing the magnitude of the former. Circadian pattern of contraction and expansion of diameter was less evident in the fruit. Under N-deficiency, distribution of 13 C and 15 N decreased and increased to fruits respectively. Restricted partitioning of carbon to fruits could be responsible for accumulation of unused assimilates and consequential osmotic adjustment for maintenance of stem water potential. This effect might have precluded contraction of stem diameter of N-deficient plants until the production of assimilates became limiting on account of depression of leaf photosynthesis.