Periderm Tubes: an Addition to the List of Microscopic Bark Features

IAWA JournalAuthor 38 (4), – Title 2017: 571–572 571

Short communication Periderm tubes: an addition to the List of microscopic bark features

Simcha Lev-Yadun Department of Biology & Environment, Faculty of Natural Sciences, Haifa University - Oranim, Tivon 36006, Israel e-mail: [email protected]

The IAWA List of microscopic bark features (Angyalossy et al. 2016) is a very important tool for studying bark anatomy, development, ecology, and evolution. This is especially so since bark was always studied dramatically less than wood for several reasons. Naturally, wood being one of the most important renewable natural resources, with an annual global commercial value that bypasses the annual budgets of many nations, and being the major source of energy for a considerable percentage of hu- manity, has received much more attention. In addition, sectioning mature barks for microscopy is much more problematic (Roth 1981). The current increasing trend of cloning genes from bark, some of which may have significant economic potential for pharmaceutical and other industries (Lev-Yadun 2011), has slowly caused an increased interest in certain barks. One type of bark anatomy, published in the IAWA Bulletin (Aloni & Peterson 1991; Lev-Yadun & Aloni 1991) was omitted from Angyalossy et al. (2016), i.e., cork tubes formed around fiber strands of the bark when their ends emerge from the bark and are exposed to the air. This type of structure (fig. 1–9 in Aloni & Peterson 1991; fig. 1–8 inLev-Yadun & Aloni 1991; Fig. 1 & 2 here) is formed regularly when fiber strands are exposed to the atmosphere after the outer parts of the bark are shed or damaged. It was found first in Vitis vinifera as a normal ontogenetic phenomenon (Aloni & Peterson 1991), and was later induced in the barks of Melia azedarach, Ficus sycomorus and Platanus acerifolia, in experiments conducted in order to test the aeration hypothesis (Lev-Yadun & Aloni 1991). The formation of these cork tubes isolate the live bark tissues from desiccating exposure to the air. They are formed because long fiber strands with ends exposed to the atmosphere serve as highways for air, and possibly also for pathogens. Thus, these cork strands that encapsulate the fiber bands and form cork tubes, may be considered as a special type of wound periderm. They are formed only around fiber bands because air, the trigger for their formation, enters the bark and desiccates it only along the fiber bands that became exposed to air. Since long fiber strands characterize the barks of thousands of species (Esau 1969; Roth 1981; Fahn 1990; Angyalossy et al. 2016), such periderm tubes are expected to occur in many species with aging and after wounding because of various biotic and abiotic reasons. It is probable that they were overlooked because of the limited interest in old parts of the bark.

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Figure 1. A longitudinal radial section in the outer bark of a wounded trunk of Melia azedarach stained with safranin and fast-green, showing two red colored lignified fiber bands that extended out of the wound into the air. Wound cork, light-brownish in color is formed around the fiber bands and also covering the wounded surface. Figure 2. A cross section in the outer bark of a wounded trunk of Melia azedarach stained with safranin and fast-green, showing several red colored lignified fiber bands that extended out of the wound into the air about one cm below the level of sectioning. Wound cork, light-brown in color is formed around the fiber bands.

References Aloni R, Peterson CA. 1991. Naturally occurring periderm tubes around secondary phloem fibres in the bark of Vitis vinifera L. IAWA Bull. n.s. 12: 57–61. Angyalossy V, Pace MR, Evert RF, Marcati CR, Oskolski AA, Terrazas T, Kotina E, Lens F, Mazzoni-Viveiros SC, Angeles G, Machado SR, Crivellaro A, Rao KS, Junikka L, Nikolaeva N, Baas P. 2016. IAWA List of microscopic bark features. IAWA J. 37: 517– 615. Esau K. 1969. The phloem. Gebrüder Borntraeger, Berlin. Fahn A. 1990. Plant anatomy. Ed. 4. Pergamon Press, Oxford. Lev-Yadun S. 2011. Bark. Version 2. In: Encyclopedia of life sciences. John Wiley & Sons, Ltd., Chichester. doi: 10.1002/9780470015902.a0002078.pub2. Lev-Yadun S, Aloni R. 1991. Wound-induced periderm tubes in the bark of Melia azedarach, Ficus sycomorus and Platanus acerifolia. IAWA Bull. n.s. 12: 62–66. Roth I. 1981. Structural patterns of tropical barks. Gebrüder Borntraeger, Berlin. Accepted: 4 July 2017

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