Continuous light may induce photosynthetic downregulation in onion - Consequences for growth and biomass partitioning

Natasja C. Van Gestel, April D. Nesbit, Elizabeth P. Gordon, Cary Green, Paul W. Paré, Leslie Thompson, Ellen B. Peffley, David T. Tissue

Research output: Contribution to journalArticle

35 Scopus citations

Abstract

Onions were grown in environmentally controlled growth chambers for 85 days to investigate the effect of relatively low light intensity (350 μmol m -2 s-1) at two different total irradiance periods (12-h and 24-h photoperiods) on growth and photosynthetic performance. To test whether photosynthetic downregulation occurred due to carbohydrate feedback, we used onions that differed in bulb-forming capacity. Allium fistulosum (L. cv. 'Kinka') is a non-bulbing onion, with potentially limited carbohydrate storage capacity, while Allium cepa (L. cv. 'Cal 296') is a bulb-forming onion with possibly greater carbohydrate storage capacity. In A. fistulosum, photosynthetic downregulation was observed in 24-h plants as indicated by reductions in the light- and CO2-saturated photosynthetic capacity (Asat and Amax, respectively) by 26%, reduced maximum rate of carboxylation (Vcmax) by ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco) by 33%, reduced maximum rate of electron transport (Jmax) by 27% and 3-fold higher foliar sugar concentration. In contrast, the photosynthetic and biochemical capacity of A. cepa was not affected by exposure to 24-h photoperiod, presumably because substantial amounts of foliar carbohydrates were re-allocated to bulbs. In 24-h A. cepa, up to 84% of total plant mass was allocated to bulbs, while in 12-h plants, more mass was allocated to leaves. Production of greater leaf area in 12-h plants compared with 24-h plants compensated for lower total daily irradiance such that 12-h and 24-h plants of both species exhibited similar daily total leaf net CO2 exchange and plant mass at the end of the experiment.

Original languageEnglish
Pages (from-to)235-246
Number of pages12
JournalPhysiologia Plantarum
Volume125
Issue number2
DOIs
StatePublished - Oct 2005

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