Abstract
BackgroundThe decline of photosynthesis in plants under low sink demand is well known. Previous studies focused on the relationship between stomatal conductance (g s) and net photosynthetic rate (P n). These studies investigated the effect of changes in Photosystem II (PSII) function on the P n 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.Methodology/Principal FindingTwo-month-old bean plants were processed by removing pods and flowers (low sink demand). On the 1st day after low sink demand treatment, a decline of P n was accompanied by a decrease in g s and internal-to-ambient CO2 concentration ratio (C i/C a). From the 3rd to 9th day, P n and g s declined continuously while C i/C a 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 5th day. From the 11th to 21st day, P n and g s 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 φ Po, φ Eo and ψ Eo in the treatment were lower than in control; however, C i/C a values in the treatment gradually increased and were significantly higher than control on the 21st day.ConclusionsStomatal 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 P n under low sink demand. Non-stomatal limitation during the late stages after the removal of the sink of roots and pods may also cause P n 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.
Highlights
The hypothesis for the end-product inhibition of photosynthesis was proposed over a century ago [1]
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 photosynthetic rate (Pn) under low sink demand
The non-stomatal limitation was associated with the inhibition of Photosystem II (PSII) electron transport chain
Summary
The hypothesis for the end-product inhibition of photosynthesis was proposed over a century ago [1] According to this concept, owing to low sink demand, the accumulation of assimilates in source leaves may be responsible for the reduction of the photosynthetic rate. This reduction is accomplished by inhibiting the activities of the related metabolic enzymes as a direct feedback, which is called feed forward [2,3]. 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. Little is known about its effects on different limiting steps of electron transport chain in PSII under this condition
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call