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. 2020 Jul 17;20(1):339.
doi: 10.1186/s12870-020-02516-y.

Dynamic light caused less photosynthetic suppression, rather than more, under nitrogen deficit conditions than under sufficient nitrogen supply conditions in soybean

Yu-Ting Li  1   2   3 , Ying Li  1   2 , Yue-Nan Li  1   3 , Ying Liang  1   3 , Qiang Sun  4 , Geng Li  5   6 , Peng Liu  7   8 , Zi-Shan Zhang  9   10 , Hui-Yuan Gao  1   3
Affiliations

Dynamic light caused less photosynthetic suppression, rather than more, under nitrogen deficit conditions than under sufficient nitrogen supply conditions in soybean

Yu-Ting Li et al. BMC Plant Biol. .

Abstract

Background: Plants are always exposed to dynamic light. The photosynthetic light use efficiency of leaves is lower in dynamic light than in uniform irradiance. Research on the influence of environmental factors on dynamic photosynthesis is very limited. Nitrogen is critical for plants, especially for photosynthesis. Low nitrogen (LN) decreases ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and thus limits photosynthesis. The decrease in Rubisco also delays photosynthetic induction in LN leaves; therefore, we hypothesized that the difference of photosynthetic CO2 fixation between uniform and dynamic light will be greater in LN leaves compared to leaves with sufficient nitrogen supply.

Results: To test this hypothesis, soybean plants were grown under low or high nitrogen (HN), and the photosynthetic gas exchange, enzyme activity and protein amount in leaves were measured under uniform and dynamic light. Unexpectedly, dynamic light caused less photosynthetic suppression, rather than more, in LN leaves than in HN leaves. The underlying mechanism was also clarified. Short low-light (LL) intervals did not affect Rubisco activity but clearly deactivated fructose-1,6-bisphosphatase (FBPase) and sedoheptulose-1,7-bisphosphatase (SBPase), indicating that photosynthetic induction after a LL interval depends on the reactivation of FBPase and SBPase rather than Rubisco. In LN leaves, the amount of Rubisco decreased more than FBPase and SBPase, so FBPase and SBPase were present in relative excess. A lower fraction of FBPase and SBPase needs to be activated in LN leaves for photosynthesis recovery during the high-light phase of dynamic light. Therefore, photosynthetic recovery is faster in LN leaves than in HN leaves, which relieves the photosynthetic suppression caused by dynamic light in LN leaves.

Conclusions: Contrary to our expectations, dynamic light caused less photosynthetic suppression, rather than more, in LN leaves than in HN leaves of soybean. This is the first report of a stress condition alleviating the photosynthetic suppression caused by dynamic light.

Keywords: Dynamic light; Low nitrogen; Photosynthesis; Soybean.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Substance content and steady-state photosynthetic gas exchange. The specific leaf area (SLA; a), total chlorophyll (Chl) and nitrogen (N) contents (b), light intensity response curve of the net photosynthetic rate (Pn; c), transpiration rate (E; d), stomatal conductance (Gs; e) and intercellular CO2 concentration (Ci; f) as well as the photosynthetic quantum yield (PQY; plot c insert) in the leaves of high nitrogen (HN; filled)- and low nitrogen (LN; closed)-supplied plants. Means ± SD, n = 6. The asterisks indicate significant differences at P < 0.05 between HN and LN leaves (T-test)
Fig. 2
Fig. 2
Photosynthetic gas exchange under changing light conditions. The time course of the net photosynthetic rate (Pn; a, b) under changing light in the leaves of high nitrogen (HN; black) and low nitrogen (LN; grey) supply plants. The bar above the plot (a) shows the high (1600 μmol m− 2 s− 1; HL; white bar) and LL (100 μmol m− 2 s− 1; LL; grey bar) periods. The leaves were adapted under HL for 20–40 min until the Pn stabilized, after which the leaves were exposed to changing light. The grey bars, from left to right, represent 60, 120, 300, and 600 s of LL. The original Pn is shown in plot (a). In plot (b), the Pn under steady HL was taken as 100%, and the Pn under changing light conditions was calculated as a percentage of the Pn under steady HL. (c) The induction state of Pn (IS%) after LL intervals of different durations. (d-g) The integrated Pn during HL following 60 (d), 120 (e), 300 (f) or 600 s (g) LL intervals. Means ± SD, n = 6. The asterisks indicate significant differences at P < 0.05 between HN and LN leaves (T-test)
Fig. 3
Fig. 3
Photosynthetic gas exchange under fluctuating light conditions. The time course of the net photosynthetic rate (Pn; a, b) under fluctuating light in the leaves of high nitrogen (HN; black) and low nitrogen (LN; grey) supply plants. The bar above the plot (a) shows the high (1600 μmol m− 2 s− 1; HL; white bar) and LL (100 μmol m− 2 s− 1; LL; grey bar) periods. The leaves were adapted under HL (1600 μmol m− 2 s− 1) for 20–40 min until the Pn stabilized, after which the leaves were exposed to fluctuating light such that the light intensity alternated between high (1600 μmol m− 2 s− 1) and low (100 μmol m− 2 s− 1) conditions every 120 s. The original Pn is shown in plot (a). In plot (b), the Pn under steady HL was taken as 100%, and the Pn under changing light conditions was calculated as a percentage of the Pn under steady HL. (b) The maximum Pn during the HL period (Pnmax) in HN- and LN-supplied plants; the Pn under steady HL was taken as 100%, and the Pnmax was calculated as a percentage of the Pn under steady HL. (c) The integrated Pn during fluctuating light in HN- and LN-supplied plants. Means ± SD, n = 6. The asterisks indicate significant differences at P < 0.05 between HN and LN leaves (T-test)
Fig. 4
Fig. 4
RuBP carboxylation and regeneration capacity. The intercellular CO2 concentration (Ci) response curve of the net photosynthetic rate (Pn; a, b); the maximum rates of RuBP-carboxylation (Vcmax; c); the maximum rates of RuBP regeneration (Jmax; d); and the amounts of Rubisco, SBPase and FBPase (e) in the leaves of high nitrogen (HN; filled)- and low nitrogen (LN; closed)-supplied plants. In plot e, 1/2 and 1/4 indicate the quantity of protein sample loaded, and the number to the right of the bands indicates the protein content in LN leaves as a percentage of that in HN leaves. The original, full-length gel and blot were listed in Additional file 5. Means ± SD, n = 6 (gas exchange) or 3 (immunoblot). The asterisks indicate significant differences at P < 0.05 between HN and LN leaves (T-test)
Fig. 5
Fig. 5
Enzyme activity under steady and dynamic conditions. The activity of Rubisco (a, f), FBPase (b, g) and SBPase (d, i) as well as the ratios of activity between FBPase and Rubisco (c, h) and between SBPase and Rubisco (e, j) in the leaves of high nitrogen (HN; filled)- and low nitrogen (LN; closed)-supplied plants under dynamic light. The bar above the plot (a) shows the high (1600 μmol m− 2 s− 1; HL; white bar) and LL (100 μmol m− 2 s− 1; HL; grey bar) periods. The leaves under changing light (a-e) were adapted under HL for 20–40 min, and the leaves were then exposed to LL for 600 s, after which the light was changed to HL for 180 s. The leaves under fluctuating light (f-j) were adapted under HL for 20–40 min, after which the leaves were exposed to fluctuating light such that the light intensity alternated between high (1600 μmol m− 2 s− 1) and low (100 μmol m− 2 s− 1) every 120 s for 32 min. Means ± SD, n = 6. Different letters indicate significant differences at P < 0.05 between different treatments (T-test)
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