Figure 1.

Leaf initiation depends on light signaling. Soil-grown tomato seedlings were grown under 16-h days (A) or transferred to darkness for 6 d (B). Dissected shoot apices were kept in 16-h days (C) or transferred to darkness for 6 d (D); close-ups of the apices are shown above, and apices with stems are shown below. (E) Dark-treated apices that were returned to the light for an additional 10 d resumed vigorous growth. (F) Dark-treated seedlings that were returned to the light similarly resumed vigorous growth. (G) Seedlings of the aurea mutant were grown as the wild type in A. (H–J) Newly initiated primordia were counted. Numbers above bars indicate the percent of flowering. Error bars show SD (n = 10). The result was reproducible in three independent experiments. (Yellow arrows) Leaf primordia. (White dotted boxed regions) Shoot apical meristem. Note that leaf initiation stops in darkness in both soil-grown seedlings and apices cultured with sucrose. Moreover, the inhibitory effect of darkness is reversible. Apices cultured with 0.5 μM (N,O) and 5 μM (P,Q) norflurazon. (L,M) As controls, apices were cultured without norflurazon but with 0.1% EtOH. In L, N, and P, to confirm the effects of norflurazon, newly initiated leaves were removed. Note that not only the apex but also the stem is bleached. (M,O,Q) Close-ups of shoot apices in L, N, P; chlorophyll autofluorescence images of the apices are shown below. (K) Number of newly initiated leaves in control and norflurazon-treated apices. Numbers above bars indicate the percent of flowering. Error bars show SD (n > 8). The result was reproducible in three independent experiments. Note that inhibition of photosynthesis does not interfere with leaf initiation. Wild-type (R) and representative phenotypes of aurea seedlings (S–U). (S) Abnormal leaf positioning. (T) Smaller meristem. (U) In rare cases, the mutant apex developed two meristems. Divergence angles of wild-type seedlings in long days (V), aurea mutant seedlings in long days (W), wild-type plants in short days (X), and aurea mutant plants in short days (Y). The mutants display a more severe phenotype in short days than in long days. We underestimated the deviation from wild-type (wt) phyllotaxis because we were not able to dissect the ∼10% mutant plants with phenotypes too severe to allow meristem dissection. Yellow bars, 1 cm; green bars, 1 mm; white bars, 100 μm.