La orquídea C. jenmanii es una planta de interés ornamental endémica de Venezuela. En este trabajo se comparó la epidermis foliar en condiciones de orquideario, multiplicación in vitro y aclimatización. Se cultivaron plantas adultas en orquideario y líneas in vitro en medio Murashige-Skoog. Las vitroplantas enraizadas fueron aclimatizadas en un propagador de neblina durante una semana, cámara húmeda por cuatro semanas y orquideario durante tres semanas. Las muestras se procesaron mediante técnicas de microtecnia clásica. Las prácticas de cultivo in vitro indujeron el desarrollo de una epidermis con las siguientes alteraciones de la anatomía normal: mayor tamaño de las células típicas, menor espesor de las paredes anticlinales, menor tamaño de los estomas, además de la formación de estomas y tricomas en la superficie adaxial. En las hojas provenientes de la aclimatización hubo una tendencia a revertirse las alteraciones observadas in vitro, con el incremento de tamaño de los estomas y el engrosamiento de las paredes anticlinales de las células típicas, lo cual sugiere que para lograr su adaptación al orquideario, las hojas sufren cambios en sus células típicas conducentes al incremento de su resistencia mecánica y rigidez. Sin embargo, la permanencia de tricomas glandulares y estomas en la superficie adaxial sugieren que la adaptación de las hojas a las condiciones ex vitro no se completó durante las ocho semanas de aclimatización. Palabras clave adicionales: Propagación in vitro, aclimatización, orquídeas
The orchid C. jenmanii is an important endemic ornamental plant in Venezuela. In this research, leaf epidermal structure development under three environments (orchid house, in vitro multiplication phase and acclimatization) was compared. Adult plants were cultivated in orchid house, and organogenic lines propagated in vitro using Murashige-Skoog medium. Rooted micropropagated plants were acclimatized in a mist propagator for one week, humid chamber for four weeks, and orchid house during three weeks. The samples were processed by means of classical microtechnique procedures. The leaf epiderm in vitro development was abnormal, with increased dimensions of typical epidermic cells, reduction in anticlinal wall thickness, reduction of stomata size, and neo-formation of stomata and epidermic hairs in the adaxial surface. In contrast, leaves developed during acclimatization showed a reversion of abnormalities observed in vitro, with an increase of stomata size and anticlinal walls thickness. However, the permanence of adaxial leaf hairs and stomata suggest an incomplete adaptation of leaves to the external environment during the eight-week acclimatization.
Octoploid (2n = 56) bromegrass (Bromus inermis Leyss.) had significantly larger but fewer stomata than tetraploid (2n = 28) plants at all leaf positions sampled and on both leaf surfaces. Both ploidies showed a similar pattern of stomatal length and frequency at four positions on the culm and three positions on the individual leaf. Stomatal length increased and frequency decreased progressively from the top (LI) to lower (IA) leaves. The tip of the leaf had the largest but fewest number of stomata with the reverse for the base of the leaf.
Seven bromegrass cultivars within the octoploid level differed significantly in stomatal length and frequency of adaxial and abaxial surfaces and at five different leaf positions on the culm. ‘Carlton’ and ‘Blair’ had consistently smaller stomata with greater frequency, whereas ‘Saratoga’ and ‘Red Patch’ had larger, but fewer, stomata. Stomatal length increased while frequency decreased from L1 to L3 and leveled off from L3 to L5 (fifth leaf below panicle). Varietal differences in stomatal length and frequency were mainly associated with the center position of a leaf surface.
Correlations between the adaxial and abaxial surfaces of L1 showed highly significant positive values for both stomatal length and frequency. Stomatal length and frequency were negatively associated at either surface of LI. The ratio length ✕ frequency was affected more by stomatal frequency than length on the same leaf surface. The interrelationships among stomatal and leaf characters and tiller dry weight suggested that a cultivar with lower stomatal frequency is likely to have larger stomata, longer and wider leaves, and greater dry weight/tiller.
Light and fluorescence microscopy studies indicated that chlorophyll was absent from the guard cells of the lady slipper orchids, Paphiopedilum insigne (Wall.) Pfitz, P. insigne(hybrid), P. venustum (Wall.) Pfitz and P. harrisseanum Hort. In the guard cells of P. aureum hyeanum Hort., however, very slight red fluorescence suggested that chlorophyll and hence chloroplasts were present.
Ultrastructural studies of the lower epidermis of P. insigne (hybrid) confirmed the absence of chloroplasts in guard and epidermal cells although plastids of an unusual structure were found in these cells. In fully developed epidermal cells the plastids contained large amounts of a fibrous, possibly proteinaceous substance, spherical, lightly staining vesicles and an electron‐dense material located in reticulate and non‐reticulate regions. Additionally, latticed crystalline inclusions and plasto‐globuli were occasionally observed in the epidermal cell plastids. In plastids of fully developed guard cells the fibrous material, starch and plastoglobuli were present.
From the earliest stages of development of the epidermal tissue starch was present in both epidermal cell and guard cell plastids. At maturity, however, starch had accumulated to greater levels in the guard cell plastids and had entirely disappeared in the epidermal cell plastids. In differentiating epidermal tissue, plasmodesmata were found between neighbouring epidermal cells and between guard and epidermal cells. At maturity, plasmodesmata between guard and epidermal cells were not observed. Mitochondria were particularly abundant in guard cells. Large oil drops developed in guard and epidermal cells, being especially abundant in the former at maturity.
Our results confirm the observations of Nelson & Mayo (1975) that certain lady slipper orchids possess functional stomata the guard cells of which do not contain chloroplasts.
In the leaf epidermis of the monocotyledon Anemarrhena asphodeloides Bunge a characteristic pattern of stomata and papilla cells is developed.
The ontogeny of both kinds of specialized cells is initiated by a formative mitosis yielding one daughter cell with aberrant structure and competence.
It is shown that these distinctive cell types affect the fate of neighbouring epidermal cells. The final epidermal pattern is due to random initial events, as well as cell lineage, and cell‐to‐cell interactions during development.
The epidermis of Anemarrhena asphodeloides is composed of three distinct cell types: guard cells of the stomata, ordinary epidermal cells, and papilla cells occurring in files wedged between files of ordinary epidermal cells.
Both stomata and papilla cells have their origin from formative mitoses in the young protoderm. Their differentiation described on the basis of light and polarization microscopy involves a decrease in cell contacts and changing orientation of cellulose microfibrils of the cell wall.
These changes are discussed in relation to the pattern of cell divisions and to the modification of cell shape during epidermal development.