Stromules: Probing Formation and Function

Abstract

Stromules are plastid stroma-filled tubules that increase the surface area of the envelope and extend the reach of the plastid within the plant cell, affecting biosynthesis, metabolism, and signaling.

Figure 1.

Induction of stromules by outer envelope membrane protein overexpression. Four days after Agrobacterium infiltration of AtLACS9-GFP into N. benthamiana protoplasts, there is extensive proliferation of stromules, which appear to connect chloroplasts to one another. Size of bars, 10 μm. From Breuers et al. (2012). Image supplied by Andreas Weber.

Figure 2.

Photoconversion of mEosFP at high laser power prevents flow through a stromule, while protein flow and conversion occurs at low laser power. A and B, 100% laser power with 20 iterations was used to photoconvert mEosFP from green to red within the circle. C to E, Photoconversion of the plastid (arrow) with 1% laser power resulted in conversion to red protein that flowed through stromules. Details of the experiment and imaging can be found in Hanson and Sattarzadeh (2013).

Figure 3.

Two β-carbonic anhydrases of N. tabacum are found in stromules. βCA1 and βCA5 cDNAs were fused to a GFP coding region at the 3′ end and transiently expressed by Agroinfiltration into N. tabacum leaves. A, βCA1-GFP. B, Chlorophyll autofluorescence. C, Merge of A and B. D, βCA5-GFP. E, Chlorophyll autofluorescence. F, Merge of D and E. Green represents GFP; red represents chlorophyll Bars = 5 μm.

Figure 4.

Stromule induction during plant immune response. Transgenic N. benthamiana plant expressing N NLR immune receptor and chloroplast localized NRIP1 fused to cerulean was infiltrated with Agrobacterium containing TMV effector p50. Significant induction of stromules was observed 24 h post-p50 infiltration. Green, NRIP1-Cerulean; magenta, chloroplast autofluorescence. (Image from Eunsook Park, Jeffrey Caplan, and Dinesh-Kumar.)

Figure 5.

Association of chloroplasts and a stromule with the plasma membrane/cell wall region. Cotyledons of N. tabacum line MR220 expressing GFP from the chloroplast genome (Reed et al., 2001) were stained in 1 mg/mL propidium iodide (PI) for 20 min before being imaged. GFP excited at 488 nm, PI at 561 nm. Bar = 5 μm.