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Continuous light may induce photosynthetic downregulation in onion – consequences for growth and biomass partitioning
Author(s) -
Van Gestel Natasja C.,
Nesbit April D.,
Gordon Elizabeth P.,
Green Cary,
Paré Paul W.,
Thompson Leslie,
Peffley Ellen B.,
Tissue David T.
Publication year - 2005
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.2005.00560.x
Subject(s) - photosynthesis , allium fistulosum , rubisco , bulb , photosynthetic capacity , sugar , allium , horticulture , botany , biology , chemistry , food science
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 CO 2 ‐saturated photosynthetic capacity ( A sat and A max , respectively) by 26%, reduced maximum rate of carboxylation ( V cmax ) by ribulose‐1,5‐biphosphate carboxylase/oxygenase (Rubisco) by 33%, reduced maximum rate of electron transport ( J max ) 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 CO 2 exchange and plant mass at the end of the experiment.