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Restricted cell elongation in Arabidopsis hypocotyls is associated with a reduced average pectin esterification level.

Derbyshire P, McCann MC, Roberts K - BMC Plant Biol. (2007)

Bottom Line: We present evidence that the degree of pectin methyl-esterification (DE%) limits cell growth, and that a minimum level of about 60% DE is required for normal cell elongation in Arabidopsis hypocotyls.Low average levels of pectin DE% are associated with reduced cell elongation, implicating PMEs, the enzymes that regulate DE%, in the cell elongation process and in responses to GA.At high average DE% other components of the cell wall limit GA-induced growth.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Metabolic Biology, John Innes Centre, Norwich, UK. paul.derbyshire@bbsrc.ac.uk

ABSTRACT

Background: Cell elongation is mainly limited by the extensibility of the cell wall. Dicotyledonous primary (growing) cell walls contain cellulose, xyloglucan, pectin and proteins, but little is known about how each polymer class contributes to the cell wall mechanical properties that control extensibility.

Results: We present evidence that the degree of pectin methyl-esterification (DE%) limits cell growth, and that a minimum level of about 60% DE is required for normal cell elongation in Arabidopsis hypocotyls. When the average DE% falls below this level, as in two gibberellic acid (GA) mutants ga1-3 and gai, and plants expressing pectin methyl-esterase (PME1) from Aspergillus aculeatus, then hypocotyl elongation is reduced.

Conclusion: Low average levels of pectin DE% are associated with reduced cell elongation, implicating PMEs, the enzymes that regulate DE%, in the cell elongation process and in responses to GA. At high average DE% other components of the cell wall limit GA-induced growth.

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Growth kinetics and hypocotyl cell elongation in WT (Ler), ga1-3, and gai seedlings grown with and without exogenous gibberellic acid (GA). (A) Seedlings were grown in continuous light for 10 d with plates in a horizontal position and hypocotyl growth measured over this period. Measurements are an average taken from 5 to 15 seedlings ± SE for each time point. Arrows indicate time (3 d) at which hypocotyls were at approximately 50% of their final length. (B) Light micrographs showing phenotypes of 3-d-old seedlings described in (A) (left panel for each treatment), bar = 1 mm, and FESEM micrographs of hypocotyl epidermis (right panel for each treatment), bar = 25 μm.
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Figure 1: Growth kinetics and hypocotyl cell elongation in WT (Ler), ga1-3, and gai seedlings grown with and without exogenous gibberellic acid (GA). (A) Seedlings were grown in continuous light for 10 d with plates in a horizontal position and hypocotyl growth measured over this period. Measurements are an average taken from 5 to 15 seedlings ± SE for each time point. Arrows indicate time (3 d) at which hypocotyls were at approximately 50% of their final length. (B) Light micrographs showing phenotypes of 3-d-old seedlings described in (A) (left panel for each treatment), bar = 1 mm, and FESEM micrographs of hypocotyl epidermis (right panel for each treatment), bar = 25 μm.

Mentions: ga1-3 provides a system in which cell elongation in the hypocotyl can be rescued conditionally by exogenous application of GA, while gai provides a control for the effects of exogenous GA application. Hypocotyl growth kinetics in wild-type (WT) (Ler), ga1-3, and gai seedlings were established in a continuous light environment with plates positioned horizontally. Hypocotyl growth was measured during a period of 10 d after the culture plates were transferred to the growth room, in the presence and absence of 1 μM exogenous GA4 (Figure 1A), a concentration that restores hypocotyl length of ga1-3 to WT length [36]. In the absence of exogenous GA, WT hypocotyls elongate between 2 and 7 d, and have a final length of around 2 mm. ga1-3 required an extra day to germinate, after which hypocotyl elongation was minimal, reaching only 0.6 mm. gai hypocotyls elongate for up to 6 d, but at a slower rate than the WT, with a maximum length of about 1.6 mm. In the presence of exogenous GA, WT hypocotyls elongate between 2 and 7 d, and have final lengths of approximately 3.5 mm, and such hypocotyls grow longer and at a faster rate than without GA. ga1-3 hypocotyls respond to exogenous GA, elongating for up to 7 d, with final lengths of around 3 mm. Finally, gai does not respond to exogenous GA, having the same hypocotyl growth kinetics and final length as in the absence of the growth regulator, thus confirming its insensitivity to GA. These results are consistent with those reported previously [36]. However, in our analysis, final hypocotyl lengths are shorter, probably as a consequence of the inhibitory effects of the continuous light regime used.


Restricted cell elongation in Arabidopsis hypocotyls is associated with a reduced average pectin esterification level.

Derbyshire P, McCann MC, Roberts K - BMC Plant Biol. (2007)

Growth kinetics and hypocotyl cell elongation in WT (Ler), ga1-3, and gai seedlings grown with and without exogenous gibberellic acid (GA). (A) Seedlings were grown in continuous light for 10 d with plates in a horizontal position and hypocotyl growth measured over this period. Measurements are an average taken from 5 to 15 seedlings ± SE for each time point. Arrows indicate time (3 d) at which hypocotyls were at approximately 50% of their final length. (B) Light micrographs showing phenotypes of 3-d-old seedlings described in (A) (left panel for each treatment), bar = 1 mm, and FESEM micrographs of hypocotyl epidermis (right panel for each treatment), bar = 25 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1913053&req=5

Figure 1: Growth kinetics and hypocotyl cell elongation in WT (Ler), ga1-3, and gai seedlings grown with and without exogenous gibberellic acid (GA). (A) Seedlings were grown in continuous light for 10 d with plates in a horizontal position and hypocotyl growth measured over this period. Measurements are an average taken from 5 to 15 seedlings ± SE for each time point. Arrows indicate time (3 d) at which hypocotyls were at approximately 50% of their final length. (B) Light micrographs showing phenotypes of 3-d-old seedlings described in (A) (left panel for each treatment), bar = 1 mm, and FESEM micrographs of hypocotyl epidermis (right panel for each treatment), bar = 25 μm.
Mentions: ga1-3 provides a system in which cell elongation in the hypocotyl can be rescued conditionally by exogenous application of GA, while gai provides a control for the effects of exogenous GA application. Hypocotyl growth kinetics in wild-type (WT) (Ler), ga1-3, and gai seedlings were established in a continuous light environment with plates positioned horizontally. Hypocotyl growth was measured during a period of 10 d after the culture plates were transferred to the growth room, in the presence and absence of 1 μM exogenous GA4 (Figure 1A), a concentration that restores hypocotyl length of ga1-3 to WT length [36]. In the absence of exogenous GA, WT hypocotyls elongate between 2 and 7 d, and have a final length of around 2 mm. ga1-3 required an extra day to germinate, after which hypocotyl elongation was minimal, reaching only 0.6 mm. gai hypocotyls elongate for up to 6 d, but at a slower rate than the WT, with a maximum length of about 1.6 mm. In the presence of exogenous GA, WT hypocotyls elongate between 2 and 7 d, and have final lengths of approximately 3.5 mm, and such hypocotyls grow longer and at a faster rate than without GA. ga1-3 hypocotyls respond to exogenous GA, elongating for up to 7 d, with final lengths of around 3 mm. Finally, gai does not respond to exogenous GA, having the same hypocotyl growth kinetics and final length as in the absence of the growth regulator, thus confirming its insensitivity to GA. These results are consistent with those reported previously [36]. However, in our analysis, final hypocotyl lengths are shorter, probably as a consequence of the inhibitory effects of the continuous light regime used.

Bottom Line: We present evidence that the degree of pectin methyl-esterification (DE%) limits cell growth, and that a minimum level of about 60% DE is required for normal cell elongation in Arabidopsis hypocotyls.Low average levels of pectin DE% are associated with reduced cell elongation, implicating PMEs, the enzymes that regulate DE%, in the cell elongation process and in responses to GA.At high average DE% other components of the cell wall limit GA-induced growth.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Metabolic Biology, John Innes Centre, Norwich, UK. paul.derbyshire@bbsrc.ac.uk

ABSTRACT

Background: Cell elongation is mainly limited by the extensibility of the cell wall. Dicotyledonous primary (growing) cell walls contain cellulose, xyloglucan, pectin and proteins, but little is known about how each polymer class contributes to the cell wall mechanical properties that control extensibility.

Results: We present evidence that the degree of pectin methyl-esterification (DE%) limits cell growth, and that a minimum level of about 60% DE is required for normal cell elongation in Arabidopsis hypocotyls. When the average DE% falls below this level, as in two gibberellic acid (GA) mutants ga1-3 and gai, and plants expressing pectin methyl-esterase (PME1) from Aspergillus aculeatus, then hypocotyl elongation is reduced.

Conclusion: Low average levels of pectin DE% are associated with reduced cell elongation, implicating PMEs, the enzymes that regulate DE%, in the cell elongation process and in responses to GA. At high average DE% other components of the cell wall limit GA-induced growth.

Show MeSH
Related in: MedlinePlus