Arundina

Abstract: NewPhytol. (1977) 78, 365-372. DIURNAL STOMATAL AND ACIDITY RHYTHMS IN ORCHID LEAVES BY C. J. GOH, P. N. AV ADHANI, C. S. LOH, C. HANEGRAAF* and J. ARDITII* Department of Botany, University of Singapore, Singapore, JO (Received 28 August 19 76) SUMMARY The stomata of Arachnis cv. Maggie Oei, Aranda cv. Deborah, Arundina graminifolia, Bromheadia finlaysoniana, Cattle ya bowringiana X C. f orbesii and Spathoglottis plicata (Orchidaceae) occur only on the lower epidermis of the leaves and are located within hyper- stomatic chambers formed by cuticular ledges extending from the guard cells. Arachnis, Aranda and Cattleya have thick leaves which exhibit Crassulacean acid metabolism, and their stomata open when acidity levels are lowest, or shortly thereafter. Aranda and Arachnis require higher light intensities for sufficient deacidification to permit stomatal opening than Cattleya. Stomata of the thin-leaved Arundina, Bromheadia and Spathoglottis open during the day. The stomatal rhythms, morphology and distribution, as well as the pathways of carbon fixation and light requirements for deacidification, reflect the natural habitat of each species or the parents of the three hybrids. INTRODTJCTION Diurnal fluctuations of acidity in orchids were first reported nearly 100 years ago (Warburg, 1886). Since then there have been several reports of increased acidity as well as C0 2 uptake and stomata! opening in the dark in a number of species (Bendrat, 1929; Borriss, 1967; Coutinho, 1964, 1965, 1969, 1970; Coutinho and Schrage, 1970; Khan, 1964; Kristen , 1965; McWilliams, 1970; Milburn, Pearson and Ndegwe, 1968, Nuernbergk, 1963). More recently, dark 14C0 2 uptake and fixation have been shown to occur in the leaves of Arachnis cv. Maggie Oei (Arachnis hookeri'ana X A . flos-aeris), A. hookeriana var. luteola, A. flos-aeris, Aeridachnis cv. Bogor (Arachnis hookeriana var. luteola, X Aerides odoratum), Aerides odoratum and Cattleya (Borriss, 1967;Knauft and Arditti, 1969; Lee, 1970). Other findings suggest that certain orchids may fix carbon via the C4-dicarboxylic acid pathway (C4-PS). These include mature leaves of Arachnis cv. Maggie Oei (Lee, 1970) and possibly Cattleya (Knauft and Arditti, 1969). However, this is not the case with Arundina graminifolia, Bromheadia finlaysoniana, Coelogyne mayeriana, C. rochussenii, Cymbidium sinensis, C. cv. Cym-doris, and Eulophia keithii (Avadhani and Goh, 1974; Hatch, Slack and Johnson, 1967; Wong and Hew , 1973). Since epiphytic and saxicolic orchids exist under essentially xerophytic conditions, crassulacean acid metabolism (CAM) would hold the same advantages for them as for other xerophytes. Further, because some tropical orchids grow under high light intensities and temperatures, C4-PS would have the same value for them as for grasses under similar con- ditions. An obvious question arising from consideration of carbon fixation pathways in *Present address: Department of Developmental and Cell Biology, University of California, Irvine, CA 92717, U.S.A.

Abstract: Tenuipalpus orchidofilo n. sp. (Acari: Tenuipalpidae) is described from Brazil based on the mobile immatures and adult stages of both sexes collected on the orchid Arundina graminifolia (D. Don) Hochs.