Exogenously applied jasmonic acid induces changes in apical meristem morphology of potato stolons

Abstract

Hooked apex stolons and initial swelling stolons of potato plants were treated with 3 x 10-8 mol l-1 jasmonic acid (JA) to study the effect of this compound on histology, cell expansion and tissue differentiation. In hooked apex stolons, JA application increased the meristem thickness and reduced the length of the leaf primordia, whereas in initial swelling stolons narrowing of the apical region, absence of leaf primordia and swelling of the subapical meristem were evident. Early vascular tissue differentiation was observed in response to JA treatment, especially of xylem elements from regions proximal to the tunic. Protoxylem elements, such as tracheal elements, were present with thin primary cell walls. The cell area was measured in two zones: zone I, central mother cells situated immediately under the tunic; and zone II, rib meristem cells. JA caused a four- and six-fold increase in cell area in both zones in hooked apex stolons and initial swelling stolons, respectively. Thus, tuber formation is concluded to occur as a consequence of increased cell expansion, a reduction in the length of leaf primordia, enlargement of meristems, and early vascular tissue differentiation.

Fig. 1. Photomicrographs of apical and subapical meristem of the first (A and B) and second tuberization stage (C and D) treated with jasmonic acid (B and D), or water (control) (A and C). am, Apical meristem; cmc, central mother cells; lp, leaf primordium; pm, peripheral meristem; p, procambium; rm, rib meristem; sm, subapical meristem; t, tunica; te, tracheal elements. Bars = 250 µm (A and B), 50 µm (C) and 100 µm (D).

Fig. 2. Photomicrographs of zone I showing the effect of jasmonic acid on cell expansion and differentiation. First tuberization stage (A and B) and second tuberization stage (C and D). Control (A and C). Treated with jasmonic acid (B, D and E). te, Tracheal elements. Bars = 10 µm (A, B and E) and 25 µm (C and D).

Fig. 3. Effect of jasmonic acid on cell area in zone I and II of the first (A) and second (B) tuberization stages (n = 5, P < 0·05). Bars represent ± s.e.