Rays, intrusive growth, and storied cambium in the inflorescence stems of Arabidopsis thaliana (L.) Heynh

Abstract

Arabidopsis thaliana is a model plant used in analysis of different aspects of plant growth and development. Under suitable conditions, secondary growth takes place in the hypocotyl of Arabidopsis plants, a finding which helps in understanding many aspects of xylogenesis. However, not all developmental processes of secondary tissue can be studied here, as no secondary rays and intrusive growth have been detected in hypocotyl. However, results presented here concerning the secondary growth in inflorescence stems of Arabidopsis shows that both secondary rays and intrusive growth of cambial cells can be detected, and that, in the interfascicular regions, a storied cambium can be developed.

Fig. 1

a–i Structure and activity of the cambium in inflorescence stems of A. thaliana with secondary growth. a The cambial zone in the fascicular and interfascicular regions of the basal part of the stem (arrow). b Anticlinal divisions of fusiform initials in the cambial zone (arrow) and two rays extending from secondary phloem to secondary xylem (circles). c, d The uniseriate rays consist of a few ray cells (double arrows). e An intrusively growing lower end of a fusiform cell (arrow) at the radial edge of a neighboring fusiform cell. f Intrusive growth of the lower (arrows in frames) and upper (open arrows in frames) fusiform cell-ends in the cambial zone. g Secondary growth characterized by storied cambium in the interfascicular region of the basal part of an inflorescence stem. h Stories of fusiform cells (triple arrows) created from parenchyma cells after their radial longitudinal divisions (arrow). i Non-storied, fascicular cambium developed within a vascular bundle. Fusiform cells are arranged on different levels and the growth activity of their ends can be observed (double arrows). In the interfascicular region, both vessels and fibers are present. Abbreviations: fsc fascicular region, ifsc interfascicular region, e epidermis, cx cortex, nc non-storied cambium, sc storied cambium, V vessels, F fibers. a, b cross sections, c–i longitudinal sections. Scale bars 100 μm (a), 50 μm (g), 25 μm (b), 10 μm (c–f), 5 μm (h, i)