Copyright © 1980 Ohio Acad. Sci. 0030-0950/80/0006-0280 $1.00/0 BRIEF NOTE PRELIMINARY INVESTIGATION OF AIR BLISTERS IN PILEA CADIEREI1 BRIAN D. DOWNS, KEVIN C. VAUGHN and KENNETH G. WILSON, Dept. of Botany, Miami Univ., Oxford, OH 45056 OHIO J. SCI. 80(6): 280, 1980 A form of highly ornamental variega- amined with an Hitachi HS-9 electron tion in higher plants known as "air microscope. blisters" (Kirk and Tilney-Bassett 1967) Mueller and Greenwood (1978) ob- in which the leaves have silver or cream- served that phenolic-storing cells con- colored dotting or striping patterns is tained a blackened, osmiophilic cyto- very common. Species of the genera plasm due to the leaching of the phenolics Pilea, Begonia, Episcia, Dioscorea, Ze- from the vacuoles, obscuring cellular de- brina and Trifolium, to name but a few, tail and making any ultrastructural study have distinct air blisters. As common difficult. This same blackening was as this condition appears to be, it is per- found in the subepidermal air blister and haps surprising that it has not been ex- thus possibly indicated that these cells tensively studied. Hara (1957) investi- are also phenolic-storing cells. Figure 1 gated these plants by light microscopy shows a dark, osmiophilic phenolic-stor- but did no physiological or subcellular ing cell of the air blister of Pilea cadierei studies, and genetic data regarding these with relatively electron transparent epi- plants were summarized by Kirk and dermal and other cells. The plastids and Tilney-Bassett (1967). No likely role other organelles contained in the air for these air blisters has been considered blister cells are highly osmiophylic due to in either work. We examined air blister the presence of phenols in the cells. tissue from Pilea cadierei, commonly Phenolic crystals in the relatively large known as aluminum plant, by electron intracellular spaces adjacent to the air microscopy to determine which structures blister cells are also noted. The presence are present and to suggest what functions of these phenols differentiates the air they may serve. blister condition from variegation. The The plants of Pilea cadierei were colors associated with variegated plants, grown in a mixture of peat, perlite and i.e. the variegated Tradescantia and vermiculite under greenhouse conditions Chlorophytum, are due to the effects of at Miami University. Leaf sections were various mutant chloroplasts (Kirk and fixed in 3% glutaraldehyde in cacodylate Tilney-Bassett 1967), whereas the silver buffer, post-fixed in 1% osmium tetroxide or cream color in air-blistered plants is and dehydrated with spectral grade probably due to the high concentration of acetone. Material was infiltrated with phenolics present. These phenols may Spurr's Low Viscosity resin by gradual be flavones or similar compounds since addition to 100% acetone over an 8 Harborne (1976) and Swain (1975) ob- hour period. Ultrathin sections (< 0.1 M) served that white or cream coloration in were cut with a DuPont diamond knife, flowers is caused by high levels of flavones mounted on fine copper mesh grids, and in the petals. post-stained with aqueous uranyl acetate The chloroplasts of the cells subtending and lead citrate. Specimens were ex- the air blister tissue are characteristic shade type plastids, as described by ^anuscript received 10 April 1979 and in re- Anderson (1973) and Boardman (1977), vised form 28 January 1980 (#79-21). in which the grana are large and numer- 280 Ohio J. Sci. AIR BLISTERS IN PILEA 281 FIGURE 1. Typical phenolic cell from the air blister region of Pilea cadierei. Cell contents are intensely stained black due to the high phenolic concentration. X4,500. FIGURE 2. Shade-type plastid typical of those found in the cells subtending the air blister. X 10,000. ous, relative to the stroma lamellae, and Acknowledgments. Part of this work was supported by an undergraduate research grant irregularly arranged (fig. 2). Only the from Miami University's Alumni Affairs Office cells subtending the air blister tissue con- to Brian D. Downs, and by Miami University tain such unmistakably shade type Faculty Research Committee funds to Kenneth plastids, indicating the blister may be- G. Wilson. Thanks are extended to Dr. Martha have effectively as a light screen. Cald- Powell, Dr. Kenneth Stewart and Dr. Jerry well (1968) and others have shown that a McClure for their helpful comments. function of plant phenolics, which are at LITERATURE CITED high levels in the epidermis, is as a protec- Anderson, J. M., D. J. Goodchild and N. K. tive light screen. This finding may in- Boardman 1973 Composition of the phyto- dicate that the air blisters, with their high systems and chloroplast structures in extreme shade plants. Biochim. Biophys. Acta. 325: concentration of phenolics can effectively 573-585. screen out the ultraviolet light from the Boardman, N. K. 1977 Comparative photo- underlying tissue, resulting in some of synthesis of sun and shade plants. Ann. Rev. the chloroplasts becoming adapted for Plant Physiol. 28: 355-377. relative shade. Since most of the plants Caldwell, M. M. 1968 Solar ultraviolet radia- tion as an ecological factor for alpine plants. with air blisters were already somewhat Ecol. Mongr. 38: 243-268. shade-adapted, these protective phenolic Hansjorg, F. and H. Grisebach 1975 Bio- cells may serve as a substitute shade synthesis of cyanidin in cell cultures of during times when natural shade is Haplopappis gracilis. Phytochemistry 14: 2347-2442. absent. Hara, N. 1957 Study of the variegated The Golgi bodies of the air blister tissue leaves, with special reference to those caused by air spaces. Jap. J. Bot. 16: 86-101. were observed to bleb-off vesicles with Harborne, J. B. 1976 Functions of flavonoids dark, osmiophilic material seemingly in plants, pp. 736-774. In: Chemistry and identical to that found in the vacuole. Biochem. of Plant Pigments (T. W. Goodwin, This suggests phenolic synthesis or con- ed.) Academic Press, NY. Kirk, T. O. and R. Tilney-Bassett. 1967 The centration and packaging in the vacuoles. Plastids. W. H. Freeman and Co., London. Interestingly, Hansjorg and Grisebach Mueller, W. C. and Greenwood 1978 The (1975) found that some phenolic enzymes ultra structure of phenolic storing cells fixed appear to be localized in the microsome with caffeine. J. Exp. Bot. 29: 757-764. Swain, T. 1975 Evolution of flavonoid com- fraction, indicating an endoplasmic retic- ounds, pp. 1069-1129. In: The Flavonoids ulum or Golgi location, which supports (Harborne, Mabry and Mabry, eds.) Chap- these ultrastructural observations. man and Hale, London..