Callose deposition in the phloem plasmodesmata and inhibition of phloem transport in citrus leaves infected with "Candidatus Liberibacter asiaticus"

Eun Ji Koh, Lijuan Zhou, Donna S. Williams, Jiyoung Park, Ningyuan Ding, Yong Ping Duan, Byung Ho Kang

Research output: Contribution to journalArticle

64 Citations (Scopus)

Abstract

Huanglongbing (HLB) is a destructive disease of citrus trees caused by phloem-limited bacteria, Candidatus Liberibacter spp. One of the early microscopic manifestations of HLB is excessive starch accumulation in leaf chloroplasts. We hypothesize that the causative bacteria in the phloem may intervene photoassimilate export, causing the starch to over-accumulate. We examined citrus leaf phloem cells by microscopy methods to characterize plant responses to Liberibacter infection and the contribution of these responses to the pathogenicity of HLB. Plasmodesmata pore units (PPUs) connecting companion cells and sieve elements were stained with a callose-specific dye in the Liberibacter-infected leaf phloem cells; callose accumulated around PPUs before starch began to accumulate in the chloroplasts. When examined by transmission electron microscopy, PPUs with abnormally large callose deposits were more abundant in the Liberibacter-infected samples than in the uninfected samples. We demonstrated an impairment of symplastic dye movement into the vascular tissue and delayed photoassimilate export in the Liberibacter-infected leaves. Liberibacter infection was also linked to callose deposition in the sieve plates, which effectively reduced the sizes of sieve pores. Our results indicate that Liberibacter infection is accompanied by callose deposition in PPUs and sieve pores of the sieve tubes and suggest that the phloem plugging by callose inhibits phloem transport, contributing to the development of HLB symptoms.

Original languageEnglish (US)
Pages (from-to)687-697
Number of pages11
JournalProtoplasma
Volume249
Issue number3
DOIs
StatePublished - Jul 1 2012
Externally publishedYes

Fingerprint

Plasmodesmata
Candidatus Liberibacter asiaticus
Candidatus Liberibacter
Phloem
plasmodesmata
Citrus
callose
phloem
greening disease
Starch
leaves
Chloroplasts
sieves
starch
Coloring Agents
Infection
dyes
Bacteria
chloroplasts
infection

Keywords

  • Callose
  • Candidatus Liberibacter asiaticus
  • Huanglongbing
  • Phloem
  • Plasmodesmata
  • Plasmodesmata pore unit

ASJC Scopus subject areas

  • Plant Science
  • Cell Biology

Cite this

Callose deposition in the phloem plasmodesmata and inhibition of phloem transport in citrus leaves infected with "Candidatus Liberibacter asiaticus". / Koh, Eun Ji; Zhou, Lijuan; Williams, Donna S.; Park, Jiyoung; Ding, Ningyuan; Duan, Yong Ping; Kang, Byung Ho.

In: Protoplasma, Vol. 249, No. 3, 01.07.2012, p. 687-697.

Research output: Contribution to journalArticle

Koh, Eun Ji ; Zhou, Lijuan ; Williams, Donna S. ; Park, Jiyoung ; Ding, Ningyuan ; Duan, Yong Ping ; Kang, Byung Ho. / Callose deposition in the phloem plasmodesmata and inhibition of phloem transport in citrus leaves infected with "Candidatus Liberibacter asiaticus". In: Protoplasma. 2012 ; Vol. 249, No. 3. pp. 687-697.
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AU - Williams, Donna S.

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AU - Ding, Ningyuan

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AU - Kang, Byung Ho

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AB - Huanglongbing (HLB) is a destructive disease of citrus trees caused by phloem-limited bacteria, Candidatus Liberibacter spp. One of the early microscopic manifestations of HLB is excessive starch accumulation in leaf chloroplasts. We hypothesize that the causative bacteria in the phloem may intervene photoassimilate export, causing the starch to over-accumulate. We examined citrus leaf phloem cells by microscopy methods to characterize plant responses to Liberibacter infection and the contribution of these responses to the pathogenicity of HLB. Plasmodesmata pore units (PPUs) connecting companion cells and sieve elements were stained with a callose-specific dye in the Liberibacter-infected leaf phloem cells; callose accumulated around PPUs before starch began to accumulate in the chloroplasts. When examined by transmission electron microscopy, PPUs with abnormally large callose deposits were more abundant in the Liberibacter-infected samples than in the uninfected samples. We demonstrated an impairment of symplastic dye movement into the vascular tissue and delayed photoassimilate export in the Liberibacter-infected leaves. Liberibacter infection was also linked to callose deposition in the sieve plates, which effectively reduced the sizes of sieve pores. Our results indicate that Liberibacter infection is accompanied by callose deposition in PPUs and sieve pores of the sieve tubes and suggest that the phloem plugging by callose inhibits phloem transport, contributing to the development of HLB symptoms.

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