Plastid stromules are induced by stress treatments acting through abscisic acid

Abstract

SUMMARYStromules are highly dynamic stroma-filled tubules that extend from the surface of all plastid types in all multicellular plants examined to date. The stromule frequency (percentage of plastids with stromules) has generally been regarded as characteristic of the cell and tissue type. However, the present study shows that various stress treatments, including drought and salt stress, are able to induce stromule formation in the epidermal cells of tobacco hypocotyls and the root hairs of wheat seedlings. Application of abscisic acid (ABA) to tobacco and wheat seedlings induced stromule formation very effectively, and application of abamine, a specific inhibitor of ABA synthesis, prevented stromule induction by mannitol. Stromule induction by ABA was dependent on cytosolic protein synthesis, but not plastid protein synthesis. Stromules were more abundant in dark-grown seedlings than in light-grown seedlings, and the stromule frequency was increased by transfer of light-grown seedlings to the dark and decreased by illumination of dark-grown seedlings. Stromule formation was sensitive to red and far-red light, but not to blue light. Stromules were induced by treatment with ACC (1-aminocyclopropane-1-carboxylic acid), the first committed ethylene precursor, and by treatment with methyl jasmonate, but disappeared upon treatment of seedlings with salicylate. These observations indicate that abiotic, and most probably biotic, stresses are able to induce the formation of stromules in tobacco and wheat seedlings.

A Violaxanthin Deepoxidase Interacts with a Viral Suppressor of RNA Silencing to Inhibit Virus Amplification

“…S5A, column 4, and S6B). Chloroplast stromules, which are thin projections of stroma-filled tubules emerging from the surface of chloroplasts, have been reported to be associated with abiotic and biotic stresses (Gray et al, 2012;Krenz et al, 2012;Caplan et al, 2015). Although the biological significance of stromules remains unclear, accumulating evidence indicated that the stromules function in trafficking proteins (Krenz et al, 2012;Hanson and Sattarzadeh, 2013;Caplan et al, 2015).…”

Low-Phosphate Induction of Plastidal Stromules Is Dependent on Strigolactones But Not on the Canonical Strigolactone Signaling Component MAX2

“…Moreover, inhibition of stromule formation by norflurazon in wheat was interpreted as ABA being the causal agent of stromule formation . However, these results from Gray et al (2012) can now also be explained by inhibition of strigolactone biosynthesis by Figure 11. Lipid composition of wild-type, max2-1, and max3-9 seedlings grown on medium with (+P) our without phosphate (2P).…”

“…Stromules were shown to be induced by ABA in wheat (Triticum aestivum; Gray et al, 2012). Moreover, inhibition of stromule formation by norflurazon in wheat was interpreted as ABA being the causal agent of stromule formation .…”

“…S1). Therefore, the results of Gray et al (2012) can now be reinterpreted as indirect effects of ABA, which require active strigolactone biosynthesis. Indeed, a complex interaction between ABA and strigolactones has been observed before (López-Ráez et al, 2010).…”

“…Gray et al (2012) also used Abamine, a competitive inhibitor of 9-cis-epoxycarotenoid dioxygenase, which function in the ABA biosynthesis pathway, but not in the strigolactone biosynthesis pathway. Induction of stromules in wheat root hairs was blocked by Abamine; however, also here treatment was for 16 h, and results could thus be also be explained by an indirect effect of ABA biosynthesis on strigolactone biosynthesis.…”