JXB Advance Access originally published online on July 1, 2003
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Journal of Experimental Botany, Vol. 54, No. 389, pp. 1957-1967,
August 1, 2003
© 2003 Oxford University Press
Contrasting effects of N and P deprivation on the regulation of photosynthesis in tomato plants in relation to feedback limitation
Received 23 December 2002; Accepted 16 April 2003
1 Plant Research International, PO Box 16, 6700 AA, Wageningen, The Netherlands
2 Agrotechnological Research Institute (ATO), PO Box 17, 6700 AA, Wageningen, The Netherlands
3 Wageningen University, Department of Plant Sciences, Horticultural Production Chains Group, Wageningen, The Netherlands
4 School of Plant Biology, The University of Western Australia, Crawley WA 6009, Australia
5 Plant Ecophysiology, Utrecht University, Utrecht, The Netherlands
* Present address and to whom correspondence should be sent: Bejo Zaden BV, PO Box 50, 1749 ZH Warmenhuizen, The Netherlands. Fax: +31 226 393504. E-mail: c.degroot{at}bejo.nl
The effects were studied of both nitrogen and phosphorus limitation and irradiance on the performance and operation of photosynthesis in tomato leaves (Lycopersicon esculentum Mill.). Plants were grown at low N, high N, low P or high P supply and at two irradiances. Using mature leaves, measurements were made of the irradiance dependencies of the relative quantum efficiencies of photosystems I and II, and of the rate of carbon dioxide fixation. Measurements were also made of foliar starch and chlorophyll concentrations. The results showed that photosynthetic light-harvesting and electron-transport activity acclimate to nutrient stress and growth irradiance such that the internal relationships between electron transport by photosystems I and II do not change; the linear relationship between 
PSII, and PSI was not affected. It was also evident that under N stress photosynthesis was reduced by a decreased light absorption and by the decreased utilization of assimilates, while P stress mainly affected the carboxylation capacity. Under N stress foliar starch levels increased and the oxygen sensitivity of CO2 fixation decreased, whereas P stress resulted in decreased starch levels and increased oxygen sensitivity of CO2 fixation. The relationship between starch accumulation and oxygen sensitivity (increased starch correlated with decreased oxygen sensitivity) was always the same across the nutrient treatments. These results are consistent with N deprivation producing an increasing limitation of photosynthesis, possibly by feedback from the leaf carbohydrate pool, whereas, although P deprivation produces a decreased rate of CO2 fixation, this is accompanied by a increase in oxygen sensitivity, suggesting that feedback limitation is decreased under P stress.
Key words: Carboxylation activity, feedback limitation, light harvesting, nitrogen, phosphorus.
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