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Polyphenol oxidase affects normal nodule development in red clover (Trifolium pratense L.).

Webb KJ, Cookson A, Allison G, Sullivan ML, Winters AL - Front Plant Sci (2014)

Bottom Line: However, absence of PPO resulted in a more reduced environment in all tissues, as measured by redox potential, and caused subtle developmental changes in nodules.Developing nodules lacking PPO were longer, and there were more cell layers within the squashed cell layer (SCL), but the walls of these cells were less thickened and the cells were less squashed.Within the N2-fixing zone, bacteroids appeared more granular and were less tightly packed together, and were similar to developmentally compromised bacteroids elicited by catalase mutant rhizobia reported elsewhere.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biological, Environmental and Rural Sciences, Aberystwyth University Aberystwyth, UK.

ABSTRACT
Polyphenol oxidase (PPO) may have multiple functions in tissues depending on its cellular or tissue localization. Here we use PPO RNAi transformants of red clover (Trifolium pratense) to determine the role PPO plays in normal development of plants, and especially in N2-fixing nodules. In red clover, PPO was not essential for either growth or nodule production, or for nodule function in plants grown under optimal, N-free conditions. However, absence of PPO resulted in a more reduced environment in all tissues, as measured by redox potential, and caused subtle developmental changes in nodules. Leaves and, to a lesser extent nodules, lacking PPO tended to accumulate phenolic compounds. A comparison of nodules of two representative contrasting clones by microscopy revealed that nodules lacking PPO were morphologically and anatomically subtly altered, and that phenolics accumulated in different cells and tissues. Developing nodules lacking PPO were longer, and there were more cell layers within the squashed cell layer (SCL), but the walls of these cells were less thickened and the cells were less squashed. Within the N2-fixing zone, bacteroids appeared more granular and were less tightly packed together, and were similar to developmentally compromised bacteroids elicited by catalase mutant rhizobia reported elsewhere.

No MeSH data available.


Related in: MedlinePlus

Distribution of phenolics in nodule sections of two contrasting polyphenol oxidase (PPO) phenotypes, wild-type (WT) RC11 and RNAi RC4 plants as visualized by Raman microspectrometry overlaying an image generated by white reflected light. Raman images were collected using a 514 nm laser from 1400 to 1800 cm-1 and over-laid the same image collected by reflected white light in unstained ultrathin sections of two nodules in longitudinal section (A) WT RC11 and (B) RNAi RC4. The nodule meristem (m), epidermis (e), nodule cortex (nc), nodule parenchyma (np) and N2-fixing bacteroids (b) are clearly visible, along with the fully developed squashed cell layer (SCL). The white, dashed rectangles indicate the regions either side of the meristem where the SCL begins to differentiate; this region in another nodule is analyzed further by transmission electron microscopy (TEM) in Figure 2. The colors represent concentration of phenolics (as visualized by Raman emission at 1601 cm-1), from transparent equating with low levels of phenolics through black – purple – blue – white – green – yellow – orange – to red equating with high levels of phenolics. Bars = 200 μm.
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Figure 1: Distribution of phenolics in nodule sections of two contrasting polyphenol oxidase (PPO) phenotypes, wild-type (WT) RC11 and RNAi RC4 plants as visualized by Raman microspectrometry overlaying an image generated by white reflected light. Raman images were collected using a 514 nm laser from 1400 to 1800 cm-1 and over-laid the same image collected by reflected white light in unstained ultrathin sections of two nodules in longitudinal section (A) WT RC11 and (B) RNAi RC4. The nodule meristem (m), epidermis (e), nodule cortex (nc), nodule parenchyma (np) and N2-fixing bacteroids (b) are clearly visible, along with the fully developed squashed cell layer (SCL). The white, dashed rectangles indicate the regions either side of the meristem where the SCL begins to differentiate; this region in another nodule is analyzed further by transmission electron microscopy (TEM) in Figure 2. The colors represent concentration of phenolics (as visualized by Raman emission at 1601 cm-1), from transparent equating with low levels of phenolics through black – purple – blue – white – green – yellow – orange – to red equating with high levels of phenolics. Bars = 200 μm.

Mentions: Raman microspectrometry showed a different pattern of phenolic distribution in six WT and six RNAi nodules. Representative images of whole nodule sections from each clone are shown in Figures 1A,B. In WT RC11, SCL was as previously described (Webb et al., 2013), with a generally low phenolic signal within the nodule, and with discrete, localized stronger signal apparent in epidermal cells, in nodule cortex outside the SCL and within the infected zone containing bacteroids (Figure 1A). In RNAi RC4, generally higher levels of phenolics were distributed through the nodule, accumulated at higher levels in the regions of the plant meristem and near bacteroids (Figure 1B). The developing or developed SCL was less obvious in nodules of RNAi RC4 than WT RC11.


Polyphenol oxidase affects normal nodule development in red clover (Trifolium pratense L.).

Webb KJ, Cookson A, Allison G, Sullivan ML, Winters AL - Front Plant Sci (2014)

Distribution of phenolics in nodule sections of two contrasting polyphenol oxidase (PPO) phenotypes, wild-type (WT) RC11 and RNAi RC4 plants as visualized by Raman microspectrometry overlaying an image generated by white reflected light. Raman images were collected using a 514 nm laser from 1400 to 1800 cm-1 and over-laid the same image collected by reflected white light in unstained ultrathin sections of two nodules in longitudinal section (A) WT RC11 and (B) RNAi RC4. The nodule meristem (m), epidermis (e), nodule cortex (nc), nodule parenchyma (np) and N2-fixing bacteroids (b) are clearly visible, along with the fully developed squashed cell layer (SCL). The white, dashed rectangles indicate the regions either side of the meristem where the SCL begins to differentiate; this region in another nodule is analyzed further by transmission electron microscopy (TEM) in Figure 2. The colors represent concentration of phenolics (as visualized by Raman emission at 1601 cm-1), from transparent equating with low levels of phenolics through black – purple – blue – white – green – yellow – orange – to red equating with high levels of phenolics. Bars = 200 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4269121&req=5

Figure 1: Distribution of phenolics in nodule sections of two contrasting polyphenol oxidase (PPO) phenotypes, wild-type (WT) RC11 and RNAi RC4 plants as visualized by Raman microspectrometry overlaying an image generated by white reflected light. Raman images were collected using a 514 nm laser from 1400 to 1800 cm-1 and over-laid the same image collected by reflected white light in unstained ultrathin sections of two nodules in longitudinal section (A) WT RC11 and (B) RNAi RC4. The nodule meristem (m), epidermis (e), nodule cortex (nc), nodule parenchyma (np) and N2-fixing bacteroids (b) are clearly visible, along with the fully developed squashed cell layer (SCL). The white, dashed rectangles indicate the regions either side of the meristem where the SCL begins to differentiate; this region in another nodule is analyzed further by transmission electron microscopy (TEM) in Figure 2. The colors represent concentration of phenolics (as visualized by Raman emission at 1601 cm-1), from transparent equating with low levels of phenolics through black – purple – blue – white – green – yellow – orange – to red equating with high levels of phenolics. Bars = 200 μm.
Mentions: Raman microspectrometry showed a different pattern of phenolic distribution in six WT and six RNAi nodules. Representative images of whole nodule sections from each clone are shown in Figures 1A,B. In WT RC11, SCL was as previously described (Webb et al., 2013), with a generally low phenolic signal within the nodule, and with discrete, localized stronger signal apparent in epidermal cells, in nodule cortex outside the SCL and within the infected zone containing bacteroids (Figure 1A). In RNAi RC4, generally higher levels of phenolics were distributed through the nodule, accumulated at higher levels in the regions of the plant meristem and near bacteroids (Figure 1B). The developing or developed SCL was less obvious in nodules of RNAi RC4 than WT RC11.

Bottom Line: However, absence of PPO resulted in a more reduced environment in all tissues, as measured by redox potential, and caused subtle developmental changes in nodules.Developing nodules lacking PPO were longer, and there were more cell layers within the squashed cell layer (SCL), but the walls of these cells were less thickened and the cells were less squashed.Within the N2-fixing zone, bacteroids appeared more granular and were less tightly packed together, and were similar to developmentally compromised bacteroids elicited by catalase mutant rhizobia reported elsewhere.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biological, Environmental and Rural Sciences, Aberystwyth University Aberystwyth, UK.

ABSTRACT
Polyphenol oxidase (PPO) may have multiple functions in tissues depending on its cellular or tissue localization. Here we use PPO RNAi transformants of red clover (Trifolium pratense) to determine the role PPO plays in normal development of plants, and especially in N2-fixing nodules. In red clover, PPO was not essential for either growth or nodule production, or for nodule function in plants grown under optimal, N-free conditions. However, absence of PPO resulted in a more reduced environment in all tissues, as measured by redox potential, and caused subtle developmental changes in nodules. Leaves and, to a lesser extent nodules, lacking PPO tended to accumulate phenolic compounds. A comparison of nodules of two representative contrasting clones by microscopy revealed that nodules lacking PPO were morphologically and anatomically subtly altered, and that phenolics accumulated in different cells and tissues. Developing nodules lacking PPO were longer, and there were more cell layers within the squashed cell layer (SCL), but the walls of these cells were less thickened and the cells were less squashed. Within the N2-fixing zone, bacteroids appeared more granular and were less tightly packed together, and were similar to developmentally compromised bacteroids elicited by catalase mutant rhizobia reported elsewhere.

No MeSH data available.


Related in: MedlinePlus