However, the soybean plants grown under L and L treatments exhibited the decreased ratio of palisade and spongy thickness than treatment L These findings indicated that shade conditions or low light intensity negatively affected the soybean leaf tissue size, while an optimum light intensity significantly increased the leaf thickness, palisade tissues thickness, and spongy tissues thickness.
Figure 2. Changes in leaf structure and chloroplast structure of soybean plants as affected by different light intensity treatments. Leaf thickness A , chloroplast number B , starch grana C , thickness of palisade D , thickness of spongy tissues E , and ratio of palisade, and spongy thickness F of soybean plants under different light intensity treatments. Differences in light intensity induced the epinasty or hyponasty leaf movements in plants.
In the present study, different light intensity treatments had a significant impact on the abaxial leaf petiole angle of soybean leaves Figure 1D. A strong hyponasty an increase in abaxial leaf petiole angle was observed under light intensity treatments L and L The decrease in light intensity from L to L increase the hyponastic response in soybean plants, and minimum In addition, we measured abaxial leaf angle for continuous 15 days and all the treatments showed consistent effect on leaf angle of soybean plants, maximum under L , and minimum in treatment L Figures 1E,F.
Our results indicated that the shading conditions increased the abaxial leaf petiole angle which negatively affected the light absorption and photosynthetic process in soybean plants. To further investigate the effect of light intensity solely regulates the hyponastic response in soybean, we determined the sucrose, starch, and total soluble sugar content of soybean shoot and root at the end of day and night.
As expected, the sucrose, starch, and total soluble sugar content were significantly increased with increasing light intensity in both shoot and root. The highest sucrose content 0. The same trend was observed in root. Interestingly, under L treatment, this trend of increased sucrose, starch, and total soluble sugar content proved the epinastic movement of soybean leaves because as we mentioned above that increased light intensity L and L decreased abaxial leaf petiole angle and increased the light absorption area of soybean leaves which in turn increased the sucrose, starch, and total soluble sugar content of shoot and root due to the higher photosynthetic activity in soybean plants.
Figure 3. Changes in carbon balance of soybean plants as affected by different light intensity treatments. All the values are average of three replicates and representative of three independent experiments. The chlorophyll Chl and carotenoids Car content of soybean leaves were considerably affected by different light intensity treatments. These improvements suggesting a direct relationship of chlorophyll and carotenoids content with the changes in light intensity. Table 2. Effect of different light intensity treatments on cytochrome content Chl a, Chl b, Car and Chl a to b ratio of soybean plants.
In our study, the observations of chloroplast structure shown that chloroplast number and structure were significantly influenced by different light intensity treatments in soybean plants. The highest number of chloroplast was noticed under treatment L , while the lowest number of chloroplast was observed under L Figure 2B. Moreover, as compared to L chloroplasts under L were organized centrally in the cell and showed a more compact arrangement, and the grana stacks of chloroplast were clear and large, and every chloroplast contained 4—5 big starch grains Figure 2C.
In addition, the highest cross-sectional area of chloroplast C outer membrane, cross-sectional area of starch grains S , thylakoid to chloroplast ratio T:C , and sectional area ratio C:S were measured under L and L , respectively, while the lowest was determined under treatment L Supporting Information Table S2.
Taken together, increase light intensity significantly improved the chloroplast structure and arrangement. Furthermore, we also measured the activities of SPS and rubisco, there was a significant difference among all light intensity treatments. Acceleration in the activities of SPS and rubisco occurred in all light treatments, the amplitude of acceleration was higher in L than L , L , L , and L treatments. In our case, using the L treatment can be more effective at the enzymatic activities.
Figure 4. Changes in enzymatic activity of soybean plants as affected by different light intensity treatments. After blast against Arabidopsis, homologs of soybean were chosen to determine their gene expression levels in our experiment. Figure 5. Changes in gene expression level of soybean plants as affected by different light intensity treatments.
Table 3 shows the photosynthetic P n characteristics of soybean plants in response to different light intensity treatments. The maximum P n , G s , and C i , and T r , values of soybean plants, appeared in treatments L and L , respectively than those in L , was This increase in net photosynthetic rate indicating that light intensity is positively related with the decrease abaxial leaf petiole angle and chlorophyll contents, as light intensity L and L significantly decreased abaxial leaf petiole angle and chlorophyll contents in soybean plants.
Table 3. Effect of different light intensity treatments on photosynthetic characteristics of soybean plants. The fate of absorbed radiation energy in soybean leaves was studied in response to different light treatments Table 4.
Table 4. Effect of different light intensity treatments on chlorophyll fluorescence characteristics of soybean plants. In our study, there was a significant impact of different light intensity treatments on seed yield of soybean plants Table 5. The highest seed yield, Relative to L , soybean plants in L obtained a higher seed yield. Yield components also changed among different treatments.
Meanwhile, SW was considerably heavier in L as compared to L treatment. Table 5. The morphology of crops has certain plasticity, and corresponding adaptation mechanisms exist under different environmental conditions Gong et al. Use of higher plant population and intercropping systems are the effective ways for increasing the crop yields especially in developing countries Xie et al.
However, these methods are typically obstructed by reducing light conditions Li R. Numerous reports have confirmed that shade conditions promote the upward growth of stems and petiole while reducing the plant leaf area Kurepin et al.
However, a few experiments pay attention to the impact of changing light intensity on plant morphology. In our experiment, a gradual increase in light intensity significantly improved the stem diameter, PB, and root to shoot ratio, and decreased the plant height and hypocotyl length of soybean plants.
These results indicated that any change in light intensity directly affects the morphological parameters of soybean and low light conditions negatively affected the soybean morphology by increasing plant height and reducing stem diameter which in turn caused soybean lodging especially under intercropping conditions Liu et al. Similarly, in previous study it has been reported that decrease light intensity significantly changed the soybean morphology by reducing plant dry matter production Yang et al.
In addition, the plant height, stem diameter, and PB of soybean showed varying responses to different light intensity treatments, and these parameters may be regulated by molecular regulation networks and endogenous plant hormones Vandenbussche et al.
Overall, these results showed that L greatly improved the soybean morphology, and it is important to increase PB and stem diameter as compared to L Leaves are the main part of photosynthesis and any changes in leaf anatomy positively or negatively affected the plants photosynthesis under prevailing conditions.
It is apparent that the environmental impacts on plant leaf structure changes for every environmental factor. Results of this study confirm earlier findings Wu et al. In addition, higher light intensity mostly increases leaf thickness, palisade tissues thickness, and spongy tissues thickness of leaves as seen in our experiment and previous studies Fan et al.
This improvement in leaf thickness maybe linked with the increase in mesophyll tissue and lower light intensity produced leaves with large cell gap and loose cell arrangement, therefore palisade tissues and spongy tissues thickness decreases, it might be due to the reduced cell growth and cell layer number in palisade tissues Kalve et al. Moreover, the improve light intensity increased the palisade tissue elongation process which enhanced the chloroplast channel area through which carbon dioxide enters, consequently the thickness of leaves and photosynthetic capacity of soybean leaves significantly strengthen Terashima et al.
On average, the differences in leaf anatomy under different light intensity treatments suggesting that leaf structural components are the main targets of light and by making adjustments in leaf anatomy plants can perform better under shade stress conditions. The results of this experiment contribute to better understand soybean leaf angle and leaf movement epinastic or hyponastic behavior under changing light intensity treatments.
Normally, leaf angle is neglected in studies of photosynthesis while it is the most important factor which influences the process of photosynthesis Larbi et al. Obviously, crop leaves with orientations more horizontally to stem or perpendicular to solar radiations will absorb higher amount of solar radiations than those with more perpendicular to stem or parallel orientations to solar radiation Lovelock et al.
In the present study, the higher light intensity significantly increased leaf angle by decreasing abaxial leaf petiole angle between stem Figure 6 and leaf in L treatment than those of under L The increase in light intensity increased the PB as well as leaf biomass and area, which in result increase leaf angle due to the higher gravitational force on those leaves which had more leaf biomass as compared to those which had less leaf biomass.
Similarly, Msallem reported that higher leaf angle under normal light than those under shading conditions. On the contrary, Larbi et al. However, in accordance to our results van Zanten et al. Furthermore, carbohydrate content is the direct expression of the strong photosynthesis. Plants translocate sugar from photosynthesizing leaves to food storing cells that decides the physical fitness of plants Amiard et al.
Several past experiments concluded the role of light intensity for the synthesis of sucrose, starch, and total soluble sugar content in plants Preiss, ; Michalska et al. In our results, the sucrose, starch, and total soluble sugar content were significantly increased with increasing light intensity. These results were in agreement with the previous studies Pilkington et al.
The increase in light intensity played an important role in regulating the enzymes related to sucrose and starch Eliyahu et al.
Similarly, former studies have reported that cloudy days and low light conditions reduced the soluble sugar content in leaves Lichtenthaler et al.
Figure 6. Schematic representation of changes in leaf orientation leaf angle , physiology, and photosynthetic characteristics of soybean plants as affected by different light intensity treatments. Arrows represent the regulating directions of light intensity on soybean growth and carbon synthesis in this paper. Suppression arrow represent that reduce light intensity which negatively affect the differential growth and carbon synthesis in soybean plants by reducing the chloroplast efficiency.
Conversely, several other studies claimed that chlorophyll contents increase with the reduction in light intensity, especially contents of Chl b Li T.
Chloroplast ultrastructure controls the photosynthetic performance of crops under changing environmental conditions Shao et al. In our study, the number of chloroplast and grana were increased significantly under higher light intensity L and L treatments as compared to lower light treatment L , which suggests the beneficial effect of L and L treatments on photosynthetic apparatus of plant chloroplast ultrastructure , our findings in line with the results of Yin et al.
Anderson et al. Furthermore, the improved structure of chloroplast under higher light intensity treatments suggested that it might develop the shade-tolerant mechanism in soybean plants, especially under low light conditions.
Therefore, the optimum light intensity L improved the chloroplast ultrastructure and arrangement of soybean leaves. In addition to the effects of light intensity on morphology, leaf anatomy and chloroplast structure, our findings demonstrate that deleterious impacts of low light abolished by optimum light conditions.
There are many reasons why crop plants in shading conditions carbon would be limited. For example, Yang et al. In this study, the increase in light intensity led to enhance the net photosynthetic rate, stomatal conductance, intercellular carbon dioxide levels, and transpiration rate of soybean plants.
Thus, this showed that the improved photosynthetic parameters enhanced the carbon gain and promoted the soybean growth Liao et al. Moreover, these results suggesting that the increase in net photosynthetic rate under L and L treatments may be due to the increase in stomatal opening and the changes in net photosynthetic rate were closely associated with the stomatal opening.
Increased photosynthetic capacity is always accompanied with high quantity of electrons passing through PSII Yao et al. Chl fluorescence characteristics are one of the main important factors in photosynthetic regulation and plant responses to environmental conditions because of its sensitivity and convenience Dai et al.
In our present study, similar results were obtained, however, improved Chl fluorescence characteristics were measured under L and L treatments. These results are in line with the findings of previous reports Bahaji et al. Furthermore, the loss of Rubisco activity was recognized to be very early and fast response of crop plants to shade stress Servaites et al. Whereas, in this research the activity of Rubisco was increased with increasing light intensity, similar results were reported by Carmo-Silva and Salvucci This higher rubisco activity under higher light intensity treatments showed that the higher net photosynthetic rate of soybean plants directly correlated with rubisco activity under changing environments Zhang et al.
At high temperatures, enzymes are denatured. Chlorophyll absorbs the light required to convert carbon dioxide and water into glucose. Chlorophyll is green - so absorbs the red and blue parts of the electromagnetic spectrum and reflects the green part of the spectrum.
Leaves with more chlorophyll are better able to absorb the light required for photosynthesis. These graphs have been plotted with rate of photosynthesis against the factor under investigation. If oxygen production or carbon dioxide uptake is used as a measure of photosynthetic rate, the graphs are slightly different. The line does not go through the origin. SOD activity was assayed by measuring its ability to inhibit the photochemical reduction of nitroblue tetrazolium NBT.
The 3-mL reaction mixture contained 1. The reaction was initiated by exposing the tubes to lx light intensity for 20 min.
A nonirradiated complete reaction mixture served as a blank and another complete reaction mixture without enzyme, which gave the maximal blue color, served as a control. The reaction was stopped by quenching the irradiation light, and then the tubes were covered with a black cloth waiting for testing.
Total flavonoid concentration in the leaves of plants grown at different light intensities was measured following the method of Sakanaka et al. The reaction contained 0. After 6 min, 0. The mixture was brought to 2. The absorbance was measured immediately at nm. The results of plant growth with different light intensities on Day 45 are summarized in Table 1 and Figure 1.
Among all treatments, the plant growth was greatest in the L 30 treatment followed by L Leaf area, stem length, and fresh weight were 1. Dry weight was 1. There was no significant difference in dry weight between L 60 and L 90 treatments. Effects of four levels of light intensity on the growth of Anoectochilus formosanus per plant grown for 45 d under a controlled environment. L 10 , L 30 , L 60 , and L 90 were four light intensity treatments, in which L indicates light intensity and subscripts denote photosynthetic photon flux PPF.
Citation: HortScience horts 45, 6; The chlorophyll concentration of plants was significantly influenced by the different light intensities. Among all treatments, the chlorophyll concentration was greatest in the L 10 treatment and then decreased consistently as the light intensified, lowest in the L 90 treatment Fig. In contrast, the ratio of chlorophyll a to chlorophyll b increased to a maximum 3. Vertical bars represent se.
Probably, photoinhibition had occurred in the second leaf taken from the L 90 treatment and consequently it had the lowest ETR Fig. The ETRs of leaves including the second and third leaves were highest in the L 30 treatment followed by the L SOD activity in the L 60 treatment was 2. However, SOD activity decreased as light intensity increased to L The total flavonoid concentration of the L 60 plant was 1.
L 10 , L 30 , L 60 , and L 90 were four light intensity treatments, in which L indicates light intensity and subscripts denote photosynthetic photon flux PPF density. Light intensity is one of the key environmental factors influencing plant growth. The results clearly showed that A. Chen et al. Moreover, a light intensity either too low or too high would not be suitable to growth of A. In the present study, the plant grown under L 10 and L 90 had lower biomass and smaller leaf area.
The low biomass of plants has frequently been explained by low photosynthetic ability. The low photosynthesis can result in low growth rate. ETRs allow for the rapid and noninvasive assessment of light response of PSII and are used to study the photosynthetic performance and photoacclimation of photosynthetic organisms.
The maximum ETR was related to the maximum photosynthetic capability, which was obtained when the photosynthetic rate was limited by the activity of the electron transport chain or Calvin cycle enzymes Behrenfeld et al. As shown in Figure 3 , the L 30 plants had the highest ETRs, which contributed to a great dry weight. The L 10 and L 90 plants, however, had the lowest ETRs in the third and second leaves, respectively, which contributed to low dry weight in both treatments.
Photoinhibition may occur when light intensity exceeds what is required for the saturation of photosynthesis. Thus, the photoinhibition could account for the lower capacity of ETR as shown in the leaf from the L 90 treatment in our study.
Vasilikiotis and Melis also reported that in photoinhibition, the chloroplasts contained much of the same amount of PSII as they did under low light intensity. This is the reason why the L 10 plant with low light intensity and the L 90 plant with photoinhibition had low ETRs and resulted in low carbohydrate accumulation in both treatments.
In the present study, we also found that the ETRs in the second leaves from the L 90 treatment were lower than those from the L The phenomenon can be explained by the fact that the upper leaves may create a dense canopy to protect lower ones from photodamage during plant growth. Thus, the dry weight of plants from the L 90 treatment was greater than that from L The chlorophyll concentration of plants plays an important role in the absorption of light during photosynthesis.
In the present study, low light intensity significantly enhanced chlorophyll concentration of plants, and the chlorophyll concentration decreased as the light intensity increased. The results agree with the finding of Walters et al. The result also demonstrates that plants could balance light absorption and translation by regulating chlorophyll synthesis Bailey et al.
The change of chlorophyll concentration was possibly an acclimation of plants to different light intensities. For many plants, changes in light intensity may elicit physiological responses at the level of leaf and chloroplast Bailey et al.
In our study, the leaf responded to the light intensity by adjusting or reducing the chlorophyll concentration. SOD is an important enzyme, which contributed to clear up superoxide in plants in the case of light stress, and SOD activity can give us some valuable information whether the plant was stressed by high light. Plants can fix carbon and photosynthesize by absorbing light energy at a proper light intensity.
Excess light absorption resulted in acidic chloroplast lumen, reduced electron transport chain, and excess excitation energy EEE within chloroplast Powles, EEE is toxic for plants by producing singlet oxygen, which can cause photoinhibition mainly resulting from oxidative damage to the PSII. If these ROS are not removed immediately, they can easily cause damage to the cellular and molecular machinery, protein modification, and lipid peroxidation.
Plants have evolved various antioxidative enzymes to avoid damage. SOD is an important antioxidative enzyme, which contributes to clear up superoxide in plants. Similarly, Rabinowitch found that in scorching conditions, SOD activity decreased; without scorching, SOD activity should increase. The production of total flavonoid content can be explained by the interaction of oxidative stress and photosynthesis. It is widely believed that the synthesis of secondary metabolites in plants is part of the defense responses of plants to oxidative stress.
A number of earlier investigations have suggested that oxidative stress plays an important role for the synthesis of secondary metabolite in plant growth Wojtaszek, The greatest total flavonoid concentration found in the L 60 plants may be the result of the increased ROS induced by oxidative stress.
The secondary metabolite synthesis of plants requires endogenous signal components such as ROS Menke et al.
ROS can function as a signal for the induction of defense systems and could enhance secondary metabolite production Berglund and Ohlsson, Biology Energy In Organisms Photosynthesis.
Nov 23, Explanation: Photosynthesis, specifically the light reactions, require light to occur. The more light there is, the more photosystems in the thylakoid membrane can be activated.
Related questions Why does photosynthesis need light? Why is photosynthesis referred to as a biochemical pathway? Why is photosynthesis important for plants?
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