Effects of abscisic acid and brassinolide on photosynthetic characteristics of Leymus chinensis from Songnen Plain grassland in Northeast China
© Hu et al.; licensee Springer. 2013
Received: 22 September 2011
Accepted: 2 April 2013
Published: 2 October 2013
It has been well demonstrated that plant growth regulators have important functions in multiple physiological processes. ABA and BR play crucial roles in response of crops to stresses. Photosynthetic capacity of Leymus. chinensis treated by various concentrations of ABA and BR in combination was determined. Further more, the mechanisms of ABA and BR treatments and potential for recovery of saline-alkali grasslands were discussed.
Abscisic acid (ABA) and brassinolide (BR) affected leaf gas exchange, growth and biomass of L. chinensis. The application of ABA and BR mixtures, especially that of 0.01 mM ABA and 2 × 10-4 mM BR, increased the net photosynthetic rate, stomatal conductance, water use efficiency, the maximum net photosynthetic rate, light-saturated rate, leaf respiration rate, the maximum RUBP carboxylation rate, the maximum electron transport rate, the maximum triose-phosphate utilization, carboxylation efficiency and the quantum efficiency of PSII and subsequently enhanced density, height and biomass in L. chinensis. We also observed reduction in the light compensation and saturation points following the application of ABA and BR treatments.
We concluded that proper use of plant growth regulators can enhance the plant growth and productivity on the Songnen grassland, which is particularly important for the improvement of saline – alkaline grassland and the yield of grazing lands.
KeywordsAbscisic acid Brassinolide Leymus chinensis Photosynthetic characteristics Songnen plain grassland
It has been well demonstrated that plant growth regulators are involved in multiple physiological processes Krouk et al. (2011). Plant growth regulators are increasingly used for the improvement of plant growth and stress resistance. Recent publications reported the effects of several resistance-related hormones, including salicylic acid, jasmonates, polyamines, and 5-aminolevulinic acid (ALA), etc. on plant physiological activities. As the most studied stress-responsive hormone, abscisic acid (ABA) play crucial roles in response of plants to abiotic stresses such as drought, salinity and frost Wu (2010). For the water-stressed plants, ABA can decrease water loss via transpiration, improve the antioxidant enzymes system, and induce the expression of stress-related genes. Moreover, exogenous application of ABA significantly influences leaf photosynthesis and photosynthate accumulation through regulating stomata openness and/or activities of photosynthetic enzymes. ABA treatments show complex effects on leaf photosynthesis. Šafránková et al. (2007) found that ABA treatment significantly decreased the net photosynthetic rate (PN) and transpiration rate (E) of the water-stressed barley. ABA associated decrease in PN was also be found in Stylosanthes guianensis Zhou et al. (2006) and Pennisetum typhoides Sankhla and Huber (1974). However, several studies showed positive effects of ABA treatment on leaf photosynthesis McLaren and Smith (1977; Jia and Lu 2003; Li et al. 2006). The compromise results were also be found by Mawson et al. (1981), and Franks and Farquhar (2001). The above mentioned inconsistent results about the effects of ABA on leaf gas exchange may be caused by multiple factors, including differences in stress factors, ABA dosage and treatment time McLaren and Smith (1977).
In addition to the inconsistent effects of plant hormone on plant growth performance, the mixture of different plant hormones can produce additive action or counteraction on plant metabolism Peleg and Blumwald (2011). For example, Sankhla and Huber (1974) found that the mixture of abscisic and gibberellic acids tended to antagonize each other in incorporation of 14CO2 into photosynthetic products. Brassinolide (BR), another common plant hormone with high biological activity, is found recently in vegetables Khripach et al. (2000). BR treatments have significant effects on plant growth and stress resistance Bajguz and Hazat (2009). BR treatments lead to the increase of net photosynthetic rates Vardhini and Ramr (1998 Hou and Li 2001) or delay the reduction of photosynthetic rate Liu et al. (2008). However, the information on the influence of ABA and BR in combination on leaf photosynthesis is less available.
To date, most studies about ABA and BR are mainly focussed on crops with very few studies on perennial grasses. Leymus chinensis, a perennial grass, is the dominate species in the salinized Songnen grassland in Northeastern China Li and Zheng (1997). The Songnen grassland covers approximately 20–25% of the total area in Songnen plain and is mainly utilized for hay production and livestock grazing Li and Zheng (1997). The present study was conducted over three years within self-sown L. chinensis populations. Photosynthetic capacity of L. chinensis treated by various concentrations of ABA and BR in combination was determined. Furthermore, the mechanisms of ABA and BR treatments and potential for recovery of saline-alkali grasslands were discussed.
Study site and experimental design
This research was conducted at The Grassland Ecosystem Experimental Station of Northeast Normal University, Chang Ling Horse Breeding Farm in Jilin Province (44°30′ to 44°45′N, 123°31′ to 123°56′E), Northeast China. The study area has a typical mesothermal monsoon climate, with an altitude of 37.8 to 144.8 m. The region is cold and dry in spring with frequent wind, warm and wet in summer with frequent drought, early frosts in autumn, and long, cold winters with little snowfall. The mean annual temperature is 5.0°C with a frost–free period of 136 to 146 d. The mean annual precipitation is about 450 mm mainly occured from June to August and accounts for over 60% of the annual precipitation. The annual evaporation is 2 to 3 times higher than precipitation. Salinized meadow soil is the main soil type in the Songnen grassland.
2 × 10-4
ABA + low BR
0.01, 0.02 × 10-4
ABA + medium BR
0.01, 0.2 × 10-4
ABA + high BR
0.01, 2 × 10-4
High ABA + high BR
0.1, 2 × 10-4
ABA and BR were sprayed during the middle ten days of May in 2005 and 2006, respectively. Fully expanded leaves of plants from each plot were used to measure photosynthetic characteristics. The density, height, and biomass of the L. chinensis community were determined using standard sampling methods Shi and Guo (2006), and each measurement was repeated 5 times.
PN, gs, Ci/Ca, and E were determined using a portable open flow gas exchange system LI–6400XT (LI-COR, USA) at 2 h intervals from 8:00 h to 16:00 h. WUE was calculated as PN/E. The photosynthetically active radiation (PAR) was 1000 ± 12 μmol m-2 s-1, CO2 concentration was 350 ± 2 ppm, and leaf temperature was 26.0 ± 0.8°C. Gas exchange was measured on fully expanded leaves from the same adult plants for five plants per plot. Measurements were repeated three times for each selected plant. Moreover, measurements were done within three consecutive days in mid-July.
The responses of photosynthesis to light (A/Q)
For the measurement of A/Q, the photosynthetic photon flux density levels used for the construction of light response curves were: 2000, 1800, 1600, 1400, 1200, 1000, 800, 600, 400, 200, 100, 50 and 0 μmol m-2 s-1 generated by a LI-6400/02B red/blue light source Wu et al. (2007). The CO2 concentration was kept at 380 μmol mol-1 Wang and Zhou (2004). Each measurement was repeated 10 times between 9:00 h to 12:00 h in mid-July. All A/Q parameters were determined by fitting data to the quadratic equation described by Prioul and Chartier (1997). QE, LCP, LSE, Amax were modeled using the linearization of A/Q curves (Long and Bernacchi 2003).
The responses of photosynthesis to CO2(A/Ci)
The same process used in A/Q measurements was used for A/Ci curves. A range of CO2 concentrations (C i ), i.e. 1800, 1600, 1400, 1200, 1000, 800, 600, 400, 200, 100 and 50 μmol mol-1 was generated using a 12 g CO2 cylinder, starting from 1800 and ending at 50 μmol mol-1. The A/Ci curves were measured under four light gradients: 1200, 1000, 800 and 400 μmol m-2 s-1Dordas and Sioulas (2007). Leaf temperature was kept at 32 ± 0.8°C and each gradient of light or CO2 concentration treatment was repeated five times between 9:00 h and 10:00 h. Asat, CCP, Resp, Vcmax, Jmax, VTPU and CE were calculated according to Prioul and Chartier (1997) and Olsson and Leverenz (1994). Leaves were held in the chamber until values of photosynthesis reached a steady state. At CO2 concentration, the analysis of photosynthetic response to CO2 Field et al. (1989, Chen et al. 2006) was accompanied by a match. A model curve described by the rectangular hyperbola Olsson and Leverenz (1994) was fitted.
Chlorophyll fluorescence measurements included initial fluorescence (Fo), maximum fluorescence (Fm) and variable fluorescence (Fv). Fo refers to fluorescence when PSII reaction center opens entirely. The decrease of Fo indicates the increase of antenna hot dissipation; and the increase of Fo indicates the uneasy reversing damage of PSII reaction center. Fm refers to fluorescence when PSII reaction center closes entirely. A decrease in Fm indicates inhibition of photosynthesis. Fv, the difference between Fm and Fo, reflects a reduction in QA. The first fully expanded, healthy leaves were measured using Li–6400XT (LI-COR, USA) for dark-acclimated and light- acclimated measurements. Fo was measured after 20 min of dark acclimation during a low intensity pulsed. Fm was recorded in a 0.8 s pulse of saturating light (6500 μmol m-2 s-1).
All photosynthetic parameters were analyzed using SPSS (v. 11.0 for Windows, USA) and SigmaPlot 10. Photosynthesis Assistant was used to analyze parameters related to responses to light and CO2. The level of statistical significance was P ≤ 0.05.
Quantitative changes in plant growth parameters and plant density
Diurnal patterns of leaf gas exchange
Photosynthetic response to light (A/Q)
Photosynthetic parameters of L. chinensis in response to light under ABA and BR treatments
A max [μmol m–2 s-1]
0.02 ± 0.00d1
10.33 ± 0.93c
0.04 ± 0.00c
9.96 ± 0.85c
52.96 ± 1.94b
283.10 ± 9.56b
0.07 ± 0.00b
13.26 ± 0.67bc
52.28 ± 1.25b
255.20 ± 8.74b
ABA + low BR
0.06 ± 0.00b
13.88 ± 0.53bc
54.21 ± 1.68b
295.80 ± 10.65b
ABA + medium BR
0.07 ± 0.00b
13.64 ± 0.78bc
45.08 ± 1.34c
548.40 ± 11.28a
ABA + high BR
0.11 ± 0.00a
16.86 ± 0.91a
25.07 ± 1.25d
175.70 ± 10.34c
High ABA + high BR
0.11 ± 0.00a
14.14 ± 0.94b
24.58 ± 0.99d
157.00 ± 10.26c
The responses of photosynthesis to CO2(A/Ci)
Photosynthetic parameters of L. chinensis in responses to CO 2 ( C i ) under ABA and BR treatments
[μmol m–2 s-1]
31.16 ± 3.61 cd1
18.30 ± 1.15c
33.50 ± 2.82de
140.00 ± 2.67e
22.70 ± 1.67c
0.04 ± 0.00c
27.57 ± 4.25d
18.40 ± 1.29c
33.50 ± 2.30de
162.00 ± 2.81d
28.20 ± 1.29b
0.04 ± 0.00c
31.27 ± 2.56 cd
17.20 ± 1.05 cd
34.10 ± 2.64d
191.00 ± 3.11c
32.70 ± 1.87a
0.04 ± 0.00c
ABA + low BR
32.06 ± 3.17c
23.10 ± 2.00ab
37.90 ± 2.71c
199.00 ± 3.09c
27.00 ± 1.48b
0.07 ± 0.00b
ABA + medium BR
33.19 ± 3.89c
24.60 ± 1.65a
45.20 ± 2.35b
237.00 ± 3.47b
20.40 ± 1.95d
0.13 ± 0.00ab
ABA + high BR
49.51 ± 4.06a
25.20 ± 1.45a
51.90 ± 2.88a
262.00 ± 3.55a
25.90 ± 1.55bc
0.15 ± 0.00a
High ABA + high BR
41.93 ± 3.73b
20.80 ± 1.82b
51.10 ± 2.63a
236.00 ± 3.17b
32.80 ± 1.73a
0.14 ± 0.00ab
Discussion and conclusions
At present, global environment and crop production research lend special significance to improving plant photosynthesis, plant production and biomass through enhancing plant’s ability to resist saline-alkaline, drought and other environment stresses. Amongst others, plant growth regulators and related compounds have shown beneficial functions on the enhancement of plant growth performance and great potential to help realize those above mentioned goals.
Our experiment results indicated that the 0.01 mM ABA treatment inhibited leaf photosynthetic rate, stomatal conductance, and transpiration rate of mature L. chinensis to a certain extent, which are consistent with the results of former studies with inhibition of ABA on leaf gas exchange have been observed in several plant species Vardhini and Ramr (1998 Hou and Li 2001). We also observed that the application of 0.01 mM ABA treatment reduced the plant height and leaf quantity of the studied L. chinensis populations. However, it increased plant density, fresh mass, plant length and length width ratio of L. chinensis populations. Similar results have been reported by Saab et al. (1990) on the effects of ABA application on the growth of maize seedlings. Saab et al. (1990) found that ABA could promote the growth of maize seedling root, and inhibit stem and leaf growth under the water stress or water shortage condition. Moreover, we also found the special physiological effect of ABA treatment alone on other leaf photosynthetic parameters, such as an increase in the maximum RUBP carboxylation rate, leaf respiration rate, maximum electron transport, and maximum triose-phosphate utilization rate of L. chinensis leaves and a reduction in the light compensation point and light saturation estimates. The results of leaf chlorophyll fluorescence measurements suggest that ABA treatment enhanced anti-photoinhibition and the ability to resist harmful environments in L. chinensis. Overall, despite slightly reduction in plant height and leaf number per shoot, the gas exchange and chlorophyll fluorescence data indicate that the application of ABA alone enhanced leaf photosynthetic activities and CO2 assimilation rate.
BR is another important plant growth regulator, which has profound impacts of leaf photosynthesis and plant performance. The results of previous experiments suggest that BR improve leaf carbon assimilation rate through increasing the content of chlorophyll, which is the light harvesting machine of plant photosynthesis. Moreover, it has also showed that BR application could significantly alleviate the impacts of various abiotic stresses. For instance, BR treatment enhanced photosynthetic performance of cotton seedlings under NaCl stress Ding et al. (1995; Xiao et al. 2007; Chen et al. 2007; Shu et al. 2011). For cucumber seedlings, BR treatment has also been found to promote the occurrence of new roots and the formation of lateral roots Bao et al. (2004). Similar results were obtained in our experiment; BR treatment (2 × 10-4 mM) alone increased the photosynthetic carboxylation capacity and CO2 assimilation rate. Subsequently, BR treatment enhaned the plant density, height and biomass of the studied L. chinensis populations. As a saline alkali grassland rhizomatous plant, the occurrence of new and lateral roots is conducive for the growth as well as rhizome breeding of L. chinensis. The observed significant treatment effects of BR on L. chinensis may attribute to the stimulation of BR on the formation of new and lateral roots, which will not only directly enhance rhizome breeding and population density, but also indirectly improve plant water and nutrient uptake.
The effects of ABA or BR alone treatment on leaf gas exchange and plant performance have been conducted in various plants. However, the impacts of ABA and BR mixture on plant growth have been rarely tested, especially in perennial grasses. We studied the combined impacts of various ABA and BR mixtures on the leaf carboxylation capacity and growth performance of L. chinensis. The experimental results showed that ABA and BR treatments mixed in different proportions are evidently superior to treatments with ABA alone and BR alone on the enhancement of photosynthetic assimilation capacity and growth performance. The ABA and BR mixture treatments expressed not simply add up of the impacts of ABA and BR treatment alone, but showed compensatory effects between ABA and BR. This phenomenon is especially significant for the mixture of 0.01 mM ABA and 2 × 10-4 mM BR, which evidently increased PN, gs and WUE, as well as Amax, Asat,R esp, Vcmax, Jmax, VTpu, CE and quantum efficiency of PSII, and reduced the LCP and LSE. As a result of enhancement in photosynthetic capacity and CO2 assimilation rate, plant density, height and biomass were significantly increased in L. chinensis. Despite unclear in the underlying physiological mechanisms of the impacts of ABA and BR treatments on leaf photosynthetic capacity, the observed obvious effects of ABA and BR mixture on plant performance may attribute, to some extent, the compensatory impacts of ABA and BR treatment. For instance, BR application could improve root system and nutrient uptake, whereas ABA treatment enhanced photosynthetic capacities.
This experiment studied the impacts of ABA alone, BR alone and various mixture of ABA and BR on the performance of L. chinensis. Treatments of ABA alone or BR alone enhanced plant photosynthetic capacity and growth performance, however those effects were more significant when ABA and BR were implied in mixture. We proposed that there are compensatory effects between ABA and BR on regulating plant photosynthetic capacity and growth performance. Moreover, the experimental results provides evidence for enhancing the stress resistance of perennial plant populations and also builds a basis for recovering grasses growing under saline and alkaline conditions.
The maximum net photosynthetic rate
Light-saturated rate of net photosynthesis
Atmospheric CO2 concentration
Intercellular CO2 concentration
CO2 compensation point
Carboxylation efficiency calculated from CO2 response curve
The maximum electron transport rate
Light compensation point
Light saturation estimate
Net photosynthetic rate
Primary electron acceptor
High energy state quenching
Maximum RUBP carboxylation rate
Maximum rate of triose- phosphate utilization
Water use efficiency.
This research was supported by the National Natural Science Foundation of China (No. 31270366, 30870238, 31270445), Natural Science Foundation of Jilin Province (No. 20100577) and Program for New Century Excellent Talents in University (NCET-12-0814).
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