Figure 4.

ARK1-GFP Is Expressed in Non-Root Hair Cells and Accumulates on Growing Microtubule Plus Ends.

(A) ARK1-GFP is expressed in epidermal cells of the root, hypocotyl, cotyledon, petiole, and root tip. ARK1-GFP was coexpressed in ark1-1 35S_pro:mCherry-MAP4MBD plants. GC, guard cell; PC, pavement cell; MS, mitotic spindle; PPB, preprophase band; P, phragmoplast. Bars = 10 μm.

(B) A time-lapse montage showing ARK1-GFP accumulating on microtubule plus ends (mCherry-MAP4MBD) in cotyledon epidermal cells. Arrowheads indicate the growing microtubule plus end. Time for each frame is indicated. Bar = 5 μm.

(C) A kymograph of the yellow line scan in the last panel of (B) showing ARK1-GFP moving along growing microtubules.

(D) Graph showing that ARK1-GFP accumulates at the plus end of microtubules but still remains bound to the sidewall of microtubules. Lines represent the ratio between fluorescence intensity of one point to the mean fluorescence intensity of one line scan. The ratio was highest within 1 μm of the microtubule plus end but decreased further from the plus end. As a control, the same ratio was calculated for microtubules with mCherry-MAP4MBD. Forty-six line scans were used to measure ARK1-GFP, and 26 line scans were used to measure mCherry-MAP4MBD.

(E) A time-lapse montage showing that ARK1-GFP localizes specifically to plus ends but not minus ends. Arrowheads indicate a growing microtubule plus end. Arrows label the microtubule minus end that is depolymerizing. Bars = 5 μm.

(F) A time-lapse montage showing that ARK1-GFP does not localize to shrinking microtubule plus ends. The microtubule plus end grows (indicated by the arrowhead) and eventually depolymerizes (indicated by arrow). ARK1-GFP disappears upon microtubule depolymerization. Bars = 5 μm.