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. 2014 Jul 21;111(31):11551–11556. doi: 10.1073/pnas.1407337111

Fig. 1.

Fig. 1.

Elevated CLE45 activity suppresses protophloem sieve element differentiation and the formative cell division of the sieve element precursor cell. (A) Schematic presentation of protophloem sieve element formation in the Arabidopsis root meristem. (B) Confocal microscopy image of a propidium iodide-stained root meristem. The developing protophloem strands (one of them marked by asterisks) stand out because of their enhanced propidium iodide cell wall staining, allowing their unequivocal identification. (C and D) Expression pattern of the CVP2::NLS-VENUS fluorescent reporter in 5-d-old wild-type roots on normal media (C) or when shifted onto media containing 10 nM CLE45 for 24 h after 4 d (D). (E) Toluidine blue-stained histological cross sections of mock- and CLE45-treated roots, taken at the level of advanced metaxylem differentiation. Differentiated protophloem and metaphloem sieve elements can be recognized by their position and by the absent staining. Note differentiated metaphloem, but not protophloem, in the CLE45-treated sample. (F–I) Effects of transient CLE45 application on protophloem differentiation, monitored in CVP2::NLS-VENUS plants. White arrowheads (F and H): advanced nuclear degradation in the most apical transition zone cells. (I, composite image). (J) Reduced stele cell number in CLE45-treated plants resulting from missing cell files, counted at the position of differentiated xylem. (K) Root growth inhibition by application of CLE45 or the CLE45G6T variant. (L) Cross-sections illustrating representative phenotypes of plants expressing a CLE45::CLE45G6T transgene with delayed protophloem differentiation (Center) or delayed protophloem differentiation and missing cell file (Right). (M and N) Occurrence of gap cells (arrowhead) in the protophloem transition zone of CLE45::CLE45G6T (N), but not wild type plants (M). ***P < .001.