The maize low-lignin mutant F2bm3 shows pleiotropic effects on photosynthetic and cell wall metabolisms in response to chilling
Résumé
Maize (Zea mays L.) is one of the major crops in the world and is highly sensitive to low
temperature due to its tropical origin. Chilling may particularly affect maize during early
seedling growth by altering physiological processes including photosynthesis and cell
wall properties, leading to biomass reduction. Changes in photosynthetic and cell wall
metabolisms were investigated during a long chilling exposure in a low-lignin maize
mutant, brown midrib3 (bm3), which contains a null-mutation in the gene encoding
caffeic acid O-methyltransferase (COMT). Wild-type F2 plants and the near-isogenic F2
bm3 mutant were grown during 60 days with a day/night temperature regime of
15°C/11°C in a greenhouse. Photosynthetic pigments, non-structural sugars, cell wall
sugars, lignin, cell wall bound hydroxycinnamic acids (HCA) contents and
phenylpropanoid pathway enzyme activities were determined when the 4th leaf had fully
emerged. Results showed that the plants were smaller in response to chilling and this
was more pronounced in the mutant. However, both genotypes showed good vigor.
F2bm3 contained a two-fold increase in the level of chlorophyll a and accumulated
zeaxanthin in response to chilling compared to F2, indicating an alternative
photoprotection mechanism. Unlike the wild-type F2 line, the starch content was
reduced in the F2bm3 mutant and the sucrose/starch partitioning was increased in
F2bm3. Few changes in the non-cellulosic cell wall sugars composition could be
detected, except a higher degree of substitution of glucuronoarabinoxylan and a higher
content of β-glucan in both lines in response to chilling. The lignin content in leaves did
not significantly change. But the concentration of HCAs was increased in F2bm3 while it
decreased in F2. Furthermore, the concentration of esterified ferulic acid (FA) was
greater in F2bm3, suggesting a higher degree of cross-linking between GAX and FA
under chilling treatment. Thus, the increase in arabinose substitution on the xylan
backbone and the abundance of HCA in F2bm3 could increase cell wall extensibility,
thereby maintaining the hydration status of the cell wall in response to chilling. In
addition, the higher concentrations of HCA and chlorophyll observed in F2bm3 suggest
that HCAs could function as photoprotectors, thus enhancing chilling tolerance.
Domaines
Sciences du Vivant [q-bio]
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Poster 2019 The maize low-lignin mutant F2bm3 shows.pdf (1.41 Mo)
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