Taxonomic significance of leaf surface morphology in Aloe section Pictae (Xanthorrhoeaceae)
by Olwen M. G., Simmonds M. S. J., Smith G. F., Van Wijk A. E. (2009)
OLWEN M. GRACE1,2*, MONIQUE S. J. SIMMONDS FLS1, GIDEON F. SMITH2,3 and ABRAHAM E. VAN WYK FLS2
1 Royal Botanic Gardens, Kew, Surrey TW9 3AB, UK
2 Department of Plant Science, University of Pretoria, Pretoria 0002, South Africa
3 South African National Biodiversity Institute, Private Bag 101, Pretoria 0002, South Africa
in Botanical Journal of the Linnean Society 160: 418–428 –
Figure 1. Scanning electron micrograph of stomatal complex on adaxial leaf surface of Aloe umfoloziensis in transverse section: ec, epistomatal chamber; g, guard cell; i, inner cuticular ledge; l, lobe; o, outer cuticular ledge; s, subsidiary cell; sc, substomatal chamber. Scale bar, 10 mm.
Leaf surface morphology was analysed in 32 species representing the maculate species complex (the poorly resolved section Pictae) in the genus Aloe (Xanthorrhoeaceae).
Few comparative morphological data are available for the complex. Leaf surface and stomatal characters observed by scanning electron microscopy show taxonomically significant interspecific variation. Most species are characterized by irregularly outlined, four- to six-sided epidermal cells, the periclinal walls of which are flat and embellished with micropapillae and the anticlinal walls of which are indicated by channels on the leaf surface.
The outer stomatal pore is typically sunken or plane and surrounded by four lobes on the leaf surface that may overarch the epistomatal chamber. The guard cells have distinct outer and inner stomatal ledges.
Two geographical groups, comprising southern and east African species, are distinguishable by their leaf surface morphology. These characters are diagnostic in A. ellenbeckii, A. prinslooi and A. suffulta and support changes in the delimitation of A. greatheadii, A. macrocarpa and A. swynnertonii.
Stomatal density and distribution were determined among species of Agrostis grown under the same environmental and cultural conditions. The species studied were A. canina L., A. palustria Huds., and A. tenuis Sibth.
The Stomatal density varied significantly among the three species and among the five cultivars of A. palustris.
Density and distribution of stomata also varied with the leaf blade surface and position. The adaxial leaf surface of ‘Penncross’ creeping bentgrass had approximately three times the Stomatal density of the abaxial surface.
Stomata were distributed in parallel rows on the adaxial leaf blade surface and were scattered throughout the abaxial surface.
Stomatal density was greatest on the youngest leaves.
The structure of the mature stomatal complex of Flagellaria indica L. was studied since the Flagellariaceae is reported to be one of a handful of non-grass families with a grass-type stoma, and since relatively little is known about stomatal ultrastructure in monocots other than grasses.
Both the grass guard cell and its nucleus are dumbbell-shaped, and the walls that separate adjacent grass guard cells are perforated. Electron and fluorescence microscopy reveal that the Flagellaria guard cell lacks these features. Instead, the Flagellaria guard cell is neither dumbbell- nor kidney-shaped, its nucleus is roughly kidney-shaped, and the end walls are thickened and imperforate.
Additional structural features of the stomatal apparatus of Flagellaria include:
1) the subsidiary cells have a protuberance that underlies the middle of the guard cell and that forms an additional and innermost aperture of the pore;
2) guard and subsidiary cell walls are thickened differentially and are layered; and
3) organelles in both cell types appear to be confined to specific domains.
Although Flagellaria is closely related to grasses, it does not have a grass or dumbbell-shaped type of stomate. This suggests that the grass type of stomate may be less widespread than reported.
The epidermal structure and development of stomata in four taxa of Zingiberaceae viz: Aframomum melegueta K. Schum, Aframomum sceptrum K. Schum, Curcuma longa L. and Zingiber officinale Rosc. have been investigated.
Unicellular, eglandular trichomes are observed on the epidermis of A.sceptrum and Z.officinale.
Anomocytic stomata with agenous ontogeny, paracytic stomata with eumesogenous ontogeny and tetracytic stomata with mesoperigenous ontogeny are recorded in Z. officinale, Aframomum species and C. longa respectively.
Stomata of Z. officinale are the smallest in size (20.6 × 1.4 × 10.5 ㎛) while those of C. longa are the largest (42.5 × 31.5 × 20.2 ㎛). These two taxa also recorded the highest (43.7/㎟) and lowest (28.6/㎟) stomatal frequency respectively which suggests a linear regression of frequency on size.
Examining the qualities of epidermis can be useful in identification of some plant species. In an attempt to determine whether it can be useful in case of Epipactis Zinn, 1757: E. helleborine (L.) Crantz, E. albensis Nováková et Rydlo, E. atrorubens (Hoffm.) Besser, E. palustris (L.) Crantz, and E. purpurataSm. genera, their species have been studied.
The following qualities, essential taxonomically, have been considered: the shape and size of epidermal cells; the presence or absence of subsidiary cells – a type of stomata; the presence, build and types of trichomes.
The detailed studies proved that the identification of species of the Epipactis Zinn, 1757 genus based solely on the qualities of epidermis is not possible.
Diploid Anthoxanthum odoratum and tetraploid A. aristatum were compared with respect to stomatal guard cell lengths, and stomatal density at adaxial and abaxial surfaces of the lamina.
Further, the genome size of both species was determined by flow cytometry, and the number as well as the chromosomal distribution of 5S and 45S rDNAs were examined using FISH with ribosomal DNA (rDNA) probes.
The average length of stomatal guard cells in A. odoratum was shown to be greater than that for A. aristatum, but the ranges overlapped. Moreover, reduction in stomatal frequency was found at higher ploidy levels.The genome size was 6.863 pg/2C DNA for A. aristatum and 13.252 pg/2C DNA for A. odoratum. A. aristatum has four sites of 5S rDNA in its root-tip meristematic cells, whereas A. odoratum has six. Both species have six sites of 45S rDNA. Chromosomal localization of the rDNA varied, which suggests that chromosome rearrangements took place during Anthoxanthum genome evolution.
In the leaves of rice (Oryza sativa), stomatal initials arose from two asymmetric cell divisions and a symmetric division. Guard mother cells (GMCs) and long cells in stomatal files (LCSs) were formed through the first asymmetric division of the precursor cell of GMCs. Subsidiary cells (SCs) were produced by the second asymmetric division of subsidiary mother cells or LCSs. Following SC formation, GMCs divided once symmetrically to generate guard cells and then differentiated terminally to form mature stomata.
The developmental patterns of long cells, prickle hairs and short cells (phellem cells and silica cells) were also examined. Interestingly, we found that the different developmental stages of stomata and epidermal cells occurred in the similar location of immature leaves of the same phyllotaxis. In addition, two spacing patterns (“one stoma, one long cell” and “one short cell row”) probably exist in rice leaves.