N-deficiency damps out circadian rhythmic changes of stem diameter dynamics in tomato plant

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 At the fruiting stage, N was withdrawn from the growing medium for a period of 19 days and its effects were studied on plant biomass production, photosynthesis, partitioning of 13C and 15N, and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 suppresses the source activity more than the 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 13C and 15N decreased and increased, respectively in fruits. 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.