Journal Article

Closure of plasmodesmata in maize (<i>Zea mays</i>) at low temperature: a new mechanism for inhibition of photosynthesis

Anna Bilska and Paweł Sowiński

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 106, issue 5, pages 675-686
Published in print November 2010 | ISSN: 0305-7364
Published online September 2010 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcq169
Closure of plasmodesmata in maize (Zea mays) at low temperature: a new mechanism for inhibition of photosynthesis

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  • Ecology and Conservation
  • Evolutionary Biology
  • Plant Sciences and Forestry

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Background and Aims

Photosynthesis is one of the processes most susceptible to low-temperature inhibition in maize, a tropical C4 crop not yet fully adapted to a temperate climate. C4 photosynthesis relies on symplasmic exchange of large amounts of photosynthetic intermediates between Kranz mesophyll (KMS) and bundle sheath (BS) cells. The aim of this study was to test the hypothesis that the slowing of maize photosynthesis at low temperature is related to ultrastructural changes in the plasmodesmata between KM and BS as well as BS and vascular parenchyma (VP) cells.

Methods

Chilling-tolerant (CT) KW 1074 and chilling-sensitive (CS) CM 109 maize (Zea mays) lines were studied. The effect of moderate chilling (14 °C) on the rate of photosynthesis, photosynthate transport kinetics, and the ultrastructure of plasmodesmata linking the KMS, BS and VP cells were analysed. Additionally, the accumulation of callose and calreticulin was studied by the immunogold method.

Key Results

Chilling inhibited photosynthesis, photosynthate transfer to the phloem and photosynthate export from leaves in both lines. This inhibition was reversible upon cessation of chilling in the CT line but irreversible in the CS line. Simultaneously to physiological changes, chilling induced swelling of the sphincters of plasmodesmata linking KMS and BS cells and a decreased lumen of the cytoplasmic sleeve of plasmodesmata at the BS/VP interface in the CS line but not in the CT line. Accumulation of calreticulin, which occurred near the neck region of the closed plasmodesmata was observed after just 4 h of chilling and over-accumulation of callose at the KMS/BS and BS/VP interfaces occurred after 28 h of chilling.

Conclusions

Stronger chilling sensitivity of the CM 109 maize line compared with the KW 1074 line, shown by decreased photosynthesis and assimilate export from a leaf, is related to changes in the ultrastructure of leaf plasmodesmata at low temperature. The chain of reactions to chilling is likely to include calreticulin action resulting in rapid and efficient closure of the plasmodesmata at both KMS/BS and BS/VP interfaces. Callose deposition in a leaf was a secondary effect of chilling.

Keywords: Callose; calreticulin; chilling; electron tomography; phloem loading; photosynthesis inhibition; plasmodesmata ultrastructure; symplasmic transport; Zea mays

Journal Article.  6440 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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