ELECTRON PROBE ANALYSIS OF SILICON AND OTHER ELEMENTS IN LEAF EPIDERMAL CELLS OF THE RICE PLANT (ORYZA SATIVA L.)

By means of electron probe analysis, the effects of significant amounts of accumulation of silicon on the accumulation of calcium, potassium, magnesium, manganese, phosphorous, iron, and sodium in the silica cells of rice leaves are described. The silica cells of both the surfaces of the leaf blade and leaf sheath were studied. Silicon accumulation in the silica cells appears to decrease the amount of accumulation of potassium on both the surfaces of the leaf blade and sheath. The effect of significant amounts of silicon accumulation on the accumulation of other elements in a particular cell varies in different organs or on different surfaces of the organ of the same plant. Magnesium, manganese, iron, and phosphorus could not be detected in the adaxial epidermis of the leaf sheath and magnesium and iron in the adaxial epidermis of the leaf blade. Manganese, magnesium, and phosphorus were not detected in the abaxial epidermis of the leaf blade nor iron in the abaxial epidermis of the leaf sheath. Sodium was not revealed in either surface of the leaf blade and leaf sheath. Possible mechanisms for the effects of silicon accumulation on the accumulation of these elements in rice leaf epidermal cells are discussed.     

Development of a Superficial Meristem During Somatic Embryogenesis from Immature Cotyledons of Soybean (Glycine max L.)

Initial events were studied in the development of an embryogenicmeristem during somatic embryogenesis from in vitro culturedimmature cotyledons of soybean. The presence of 2,4-D in theculture medium led to the formation of a superficial embryogenictissue associated with the abaxial epidermis of 3 mm cotyledons.Additionally, 2,4-D initiated rapid non-morphogenic periclinaldivision in the parenchyma tissues of the cotyledon. Consequentinternal expansion disrupted and eventually ruptured the apparentlyquiescent adaxial epidermis. The profound difference in thein vitro response between abaxial and adaxial epidermes is discussedin relation to their relative roles in nutrient transport duringseed development in vivo. Somatic embryogenesis, transfer cells, Glycine max     

Structure of mucilaginous epidermal cell walls in Passerina (Thymelaeaceae)

Leaves of Passerina are inversely ericoid. Adaxial epidermal cells are relatively small; abaxial ones are large and tanniniferous. Mucilaginous epidermal cells are usually present in many Thymelaeaceae, including Passerina , mainly in the abaxial epidermis. They are unequally divided by a periclinal wall-like septum into two separate compartments: (1) the outer, adjacent to the cuticle, containing mostly tanniniferous substances and (2) the inner, containing mucilage. This type of epidermis has often been incorrecdy described as uni-, bi- or multiseriate. Transmission electron microscopy revealed mucilage, characterized by microfibrils, embedded between die innermost wall-like septum and outermost layers of the inner periclinal cell wall. As accumulation of mucilage increases, the innermost (adjacent to the cell contents) layer of the original periclinal cell wall is pressed against the cytoplasm, thus forming a clearly demarcated cellulose periclinal wall which divides the epidermis cell into two compartments, the inner wiuh mucilage and the outer comprising the cell lumen. Existing controversy is critically discussed. Our observations confirm the authenticity of mucilagination in epidermal cell walls.     

Wound-induced resistance to cellulase in oat leaves

Peeling the epidermis induces the development of resistance to cellulolytic digestion in the mesophyll cell wals of the first leaf of 1- to 3-week-old oat seedlings (Avena sativa var. Victory). Development of resistance occurs between 3 and 11 hours after the abaxial epidermis is peeled from the blade, and is inhibited by actinomycin D (20 micrograms per milliliter) or cycloheximide (1 microgram per milliliter). Other methods of wounding (cutting with a razor blade, stabbing with a dissection needle or brushing with diatomaceous silica) also induce resistance in cells near the wounds. Peeling similarly induces resistance to the digestion of mesophyll cell walls by Cellulysin (Calbiochem) in pea, corn, wheat, and barley.     

Micromorphology of the leaf epidermis in taxa of the Agropyron-Elymus complex (Poaceae)

WEBB, M. E. & ALMEIDA, M. T., 1990. Micromorphology of the leaf epidermis in taxa of the Agropyron-Elymus complex (Poaceae). A comparative analysis by scanning electron microscopy was carried out on both leaf epidermes (adaxial and abaxial) of Elymus pychnanthus (Godr.) Meld, and Agropyron glaucum Roemer & Schultes.
The adaxial epidermes of E.pychnanthus and A. glaucum are similar in the position and the shape of the long cells, silica bodies and costal and papillate prickles. They differ in the higher number of silica cells in E. pychnanthus and in the presence of intercostal hooks in A. glaucum.
The abaxial epidermes of both species are similar in the shape of interstomatal cells, silica bodies and papillate prickles. They differ in the distribution of the stomata and in the contact zones of the long cells. Elymus pychnanthus and A. glaucum differ also in the trichomes situated along the margins of the leaf blade.
These micromorphological differences, especially those of the abaxial epidermis, are useful taxonomic features.     

Evidence for long-distance, chemical gall induction by an insect

Abstract We report that a chemical stimulus from a herbivore, a galling insect, changes plant morphology and physiology to benefit the herbivore. Previous studies could not determine whether insect galls are induced by mechanical or chemical stimuli because feeding and oviposition both occurred at the site of gall formation. We report that the mouthparts of a spruce‐galling insect, Adelges cooleyi, were inserted in stem phloem cells far from induced galls, that tissues between mouthparts and galls appeared normal, and that the ability to initiate galls was inversely correlated with distance from buds (potential gall sites). Thus the effects of chemical stimuli were unambiguously separated from any mechanical influence of probing stylets or ovipositors. Our results strongly suggest that galls were induced by a chemical stimulus transported to buds via vascular tissue and that its efficacy was dose‐dependent.     

Establishment of polarity in lateral organs of plants

BACKGROUND: Asymmetric development of plant lateral organs initiates by partitioning of organ primordia into distinct domains along their adaxial/abaxial axis. A recent model proposes that a meristem-born signal, acting in a concentration-dependent manner, differentially activates PHABULOSA-like genes, which in turn suppress abaxial-promoting factors. As yet, no abaxial factors have been identified that when compromised give rise to adaxialized organs. RESULTS: Single mutants in either of the closely related genes KANADI1 (KAN1) or KANADI2 (KAN2) have little or no effect on plant morphology. However, in kan1 kan2 double mutant plants, there is a replacement of abaxial cell types by adaxial ones in most lateral organs. The alterations in polarity establishment are associated with expansion in the expression domain of the PHB-like genes and reduction in the expression of the previously described abaxial-promoting YABBY genes. Ectopic expression of either of the KANADI genes throughout leaf primordia results in dramatic transformation of adaxial cell types into abaxial ones, failure of lateral blade expansion, and vascular tissue formation. CONCLUSION: The phenotypes of KANADI loss- and gain-of-function alleles suggest that fine regulation of these genes is at the core of polarity establishment. As such, they are likely to be targets of the PHB-mediated meristem-born signaling that patterns lateral organ primordia. PHB-like genes and the abaxial-promoting KANADI and YABBY genes appear to be expressed throughout primordia anlagen before becoming confined to their corresponding domains as primordia arise. This suggests that the establishment of polarity in plant lateral organs occurs via mutual repression interactions between ab/ad factors after primordium emergence, consistent with the results of classical dissection experiments.