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CELL WALL INVERTASE 4 is required for nectar production in Arabidopsis.

Ruhlmann JM, Kram BW, Carter CJ - J. Exp. Bot. (2009)

Bottom Line: Unlike wild-type plants, cwinv4 lines did not produce nectar.Cell wall extracts prepared from mutant flowers displayed greatly reduced invertase activity when compared with wild-type plants, and cwinv4 flowers also accumulated significantly lower levels of total soluble sugar.Cumulatively, these results implicate CWINV4 as an absolutely required factor for nectar production in the Brassicaceae, specifically by maintaining constant sink status within nectaries, thus allowing them to accumulate the sugars necessary for nectar production.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, 1035 Kirby Drive, University of Minnesota-Duluth, Duluth, MN 55812, USA.

ABSTRACT
To date, no genes have been reported to directly affect the de novo production of floral nectar. In an effort to identify genes involved in nectar production, the Affymetrix((R)) ATH1 GeneChip was previously used to examine global gene expression profiles in Arabidopsis thaliana nectaries. One of the genes displaying highly enriched expression in nectaries was CELL WALL INVERTASE 4 (AtCWINV4, At2g36190), which encodes an enzyme that putatively catalyses the hydrolysis of sucrose into glucose and fructose. RT-PCR was used to confirm the nectary-enriched expression of AtCWINV4, as well as an orthologue from Brassica rapa. To probe biological function, two independent Arabidopsis cwinv4 T-DNA mutants were isolated. Unlike wild-type plants, cwinv4 lines did not produce nectar. While overall nectary morphology appeared to be normal, cwinv4 flowers accumulated higher than normal levels of starch in the receptacle, but not within the nectaries themselves. Conversely, wild-type, but not cwinv4, nectarial stomata stained intensely for starch. Cell wall extracts prepared from mutant flowers displayed greatly reduced invertase activity when compared with wild-type plants, and cwinv4 flowers also accumulated significantly lower levels of total soluble sugar. Cumulatively, these results implicate CWINV4 as an absolutely required factor for nectar production in the Brassicaceae, specifically by maintaining constant sink status within nectaries, thus allowing them to accumulate the sugars necessary for nectar production. In addition, CWINV4 is probably responsible for the hexose-rich composition observed for many Brassicaceae nectars.

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cwinv4 flowers accumulate decreased total soluble sugar. Whole flowers (Stage 14–15) from both cwinv4-1 and cwinv4-2 displayed significantly lower levels of total soluble sugar (sucrose and glucose) than wild-type plants (n=3, *P=0.027 and 0.013, respectively). Results are displayed as total absorbance per mg of floral tissue ×100. The relative proportion of sucrose-to-glucose was similar between cwinv4 and wild-type flowers (data not shown).
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fig5: cwinv4 flowers accumulate decreased total soluble sugar. Whole flowers (Stage 14–15) from both cwinv4-1 and cwinv4-2 displayed significantly lower levels of total soluble sugar (sucrose and glucose) than wild-type plants (n=3, *P=0.027 and 0.013, respectively). Results are displayed as total absorbance per mg of floral tissue ×100. The relative proportion of sucrose-to-glucose was similar between cwinv4 and wild-type flowers (data not shown).

Mentions: Related to the starch analyses described above, it seemed logical to examine whether cwinv4 mutants displayed changes in the accumulation of soluble sugars. Simple sugars were extracted from whole flowers and assayed as previously described (Bethke and Busse, 2008). Results shown in Fig. 5 demonstrate that both cwinv4-1 and cwinv4-2 flowers accumulated significantly lower levels of soluble sugars, specifically sucrose and glucose, than wild-type plants. Notably, the overall ratio of glucose-to-sucrose was similar in wild-type and cwinv4 flowers (∼90% glucose and 10% sucrose in all lines examined, data not shown).


CELL WALL INVERTASE 4 is required for nectar production in Arabidopsis.

Ruhlmann JM, Kram BW, Carter CJ - J. Exp. Bot. (2009)

cwinv4 flowers accumulate decreased total soluble sugar. Whole flowers (Stage 14–15) from both cwinv4-1 and cwinv4-2 displayed significantly lower levels of total soluble sugar (sucrose and glucose) than wild-type plants (n=3, *P=0.027 and 0.013, respectively). Results are displayed as total absorbance per mg of floral tissue ×100. The relative proportion of sucrose-to-glucose was similar between cwinv4 and wild-type flowers (data not shown).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2803206&req=5

fig5: cwinv4 flowers accumulate decreased total soluble sugar. Whole flowers (Stage 14–15) from both cwinv4-1 and cwinv4-2 displayed significantly lower levels of total soluble sugar (sucrose and glucose) than wild-type plants (n=3, *P=0.027 and 0.013, respectively). Results are displayed as total absorbance per mg of floral tissue ×100. The relative proportion of sucrose-to-glucose was similar between cwinv4 and wild-type flowers (data not shown).
Mentions: Related to the starch analyses described above, it seemed logical to examine whether cwinv4 mutants displayed changes in the accumulation of soluble sugars. Simple sugars were extracted from whole flowers and assayed as previously described (Bethke and Busse, 2008). Results shown in Fig. 5 demonstrate that both cwinv4-1 and cwinv4-2 flowers accumulated significantly lower levels of soluble sugars, specifically sucrose and glucose, than wild-type plants. Notably, the overall ratio of glucose-to-sucrose was similar in wild-type and cwinv4 flowers (∼90% glucose and 10% sucrose in all lines examined, data not shown).

Bottom Line: Unlike wild-type plants, cwinv4 lines did not produce nectar.Cell wall extracts prepared from mutant flowers displayed greatly reduced invertase activity when compared with wild-type plants, and cwinv4 flowers also accumulated significantly lower levels of total soluble sugar.Cumulatively, these results implicate CWINV4 as an absolutely required factor for nectar production in the Brassicaceae, specifically by maintaining constant sink status within nectaries, thus allowing them to accumulate the sugars necessary for nectar production.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, 1035 Kirby Drive, University of Minnesota-Duluth, Duluth, MN 55812, USA.

ABSTRACT
To date, no genes have been reported to directly affect the de novo production of floral nectar. In an effort to identify genes involved in nectar production, the Affymetrix((R)) ATH1 GeneChip was previously used to examine global gene expression profiles in Arabidopsis thaliana nectaries. One of the genes displaying highly enriched expression in nectaries was CELL WALL INVERTASE 4 (AtCWINV4, At2g36190), which encodes an enzyme that putatively catalyses the hydrolysis of sucrose into glucose and fructose. RT-PCR was used to confirm the nectary-enriched expression of AtCWINV4, as well as an orthologue from Brassica rapa. To probe biological function, two independent Arabidopsis cwinv4 T-DNA mutants were isolated. Unlike wild-type plants, cwinv4 lines did not produce nectar. While overall nectary morphology appeared to be normal, cwinv4 flowers accumulated higher than normal levels of starch in the receptacle, but not within the nectaries themselves. Conversely, wild-type, but not cwinv4, nectarial stomata stained intensely for starch. Cell wall extracts prepared from mutant flowers displayed greatly reduced invertase activity when compared with wild-type plants, and cwinv4 flowers also accumulated significantly lower levels of total soluble sugar. Cumulatively, these results implicate CWINV4 as an absolutely required factor for nectar production in the Brassicaceae, specifically by maintaining constant sink status within nectaries, thus allowing them to accumulate the sugars necessary for nectar production. In addition, CWINV4 is probably responsible for the hexose-rich composition observed for many Brassicaceae nectars.

Show MeSH