title: Response of bean (Vicia faba L.) plants to low sink demand by measuring the gas exchange rates and chlorophyll a fluorescence kinetics.
abstract: BACKGROUND
  The decline of photosynthesis in plants under low sink demand is well known. Previous studies focused on the relationship between stomatal conductance (gs) and net photosynthetic rate (Pn). These studies investigated the effect of changes in Photosystem II (PSII) function on the Pn decline under low sink demand. However, little is known about its effects on different limiting steps of electron transport chain in PSII under this condition.
  
  
  RESULTS
  Two-month-old bean plants were processed by removing pods and flowers (low sink demand). On the 1(st) day after low sink demand treatment, a decline of Pn was accompanied by a decrease in gs and internal-to-ambient CO2 concentration ratio (Ci/Ca). From the 3(rd) to 9(th) day, Pn and gs declined continuously while Ci/Ca ratio remained stable in the treatment. Moreover, these values were lower than that of control. Wk (a parameter reflecting the damage to oxygen evolving complex of the donor side of PSII) values in the treatment were significantly higher than their corresponding control values. However, RCQA (a parameter reflecting the number of active RCs per excited cross-section of PSII) values in the treatment were significantly lower than control from the 5(th) day. From the 11(th) to 21(st) day, Pn and gs of the treatment continued to decline and were lower than control. This was accompanied by a decrease of RCQA, and an increase of Wk. Furthermore, the quantum yield parameters φPo, φEo and ψEo in the treatment were lower than in control; however, Ci/Ca values in the treatment gradually increased and were significantly higher than control on the 21(st) day.
  
  
  CONCLUSIONS
  Stomatal limitation during the early stage, whereas a combination of stomatal and non-stomatal limitation during the middle stage might be responsible for the reduction of Pn under low sink demand. Non-stomatal limitation during the late stages after the removal of the sink of roots and pods may also cause Pn reduction. The non-stomatal limitation was associated with the inhibition of PSII electron transport chain. Our data suggests that the donor side of PSII was the most sensitive to low sink demand followed by the reaction center of PSII. The acceptor side of PSII may be the least sensitive.
authors: Beijing Key Laboratory of Grape Science and Enology and Key Laboratory of Plant Resources, Institute of Botany, the Chinese Academy of Sciences, Beijing, People's Republic of China ; University of Chinese Academy of Sciences, Beijing, People's Republic of China.
authors: Bo-Fang
authors: BF
authors: Yan
authors: Wei
authors: W
authors: Duan
authors: Guo-Tian
authors: GT
authors: Liu
authors: Hong-Guo
authors: HG
authors: Xu
authors: Li-Jun
authors: LJ
authors: Wang
authors: Shao-Hua
authors: SH
authors: Li
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D002734:Chlorophyll / Q000737:chemistry* / Q000378:metabolism; D000077194:Chlorophyll A; D004579:Electron Transport; D025461:Feedback, Physiological; D007700:Kinetics; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018515:Plant Leaves / Q000502:physiology*; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence; D031307:Vicia faba / Q000502:physiology*
chemical_list: D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D002245:Carbon Dioxide; D010100:Oxygen; D000077194:Chlorophyll A