Colleters in Turnera and Piriqueta (Turneraceae)

The anatomy of colleters was examined by light and scanning electron microscopy in 25 species of Turnera and nine species of Piriqueta. Based on morphology, four categories of colleters were recognized: standard, sessile, lachrymiform and trochleariform, all of which differ in shape and length/width ratio. They all have a similar anatomy: they consist of an axis of parenchymatous cells, sheathed by a palisade epidermis. The standard type is the most widespread in the studied taxa; the lachrymiform example was found in those species of Piriqueta with setiform glandular hairs; only one trochleariform example appeared in T: diffusa. The sessile type is considered to be a morphological transitional form between extrafloral nectaries and colleters. This is the first record of sessile, lachrymiform and trochleariform colleters. The anatomy of colleters is compared with other secretory structures such as glandular trichomes and extrafloral nectaries.     

Distribution and specific central projections of mechanoreceptors in the thorax and proximal leg joints of locusts

Summary Tactile hairs on the locust thorax can be divided into two classes by their external morphology and their central projection pattern: Short hairs, 10–100 m in length, which are assembled in distinct plates and rows, and long hairs, 100–800 m in length, which are distributed all over the body and are organized in large fields or aligned along the ridges of the appendages.The sensory fibers of the first class arborize in the lateral dorsal neuropile of thoracic ganglia and then extend further into the ipsilateral half of the corresponding ganglion in three main bundles from which fine rami of fibers end in the intermediate neuropile. In all three thoracic ganglia the projection pattern of homologous hair plates is similar.The sensory fibers of the second class exclusively terminate in special median ventral neuropiles, the ventral association center (VAC) and ventralmost ventral association center (VVAC). In addition fibers from meso- and metathoracic hairs, located close to the longitudinal midline of the animal, may terminate in the contralateral VAC and with one branch project to the next anterior ganglion through the ipsilateral connective. In contrast, fibers from prothoracic hairs were not found to leave their ganglion.With support by the DFG Neurale Mechanismen des VerhaltensSome of the studies were started at Universität Bielefeld, Fakultät für Biologie II (Abtlg. Prof. Dr. P. Görner)     

Die Klebstoffhaare an den Antheren vonCyclanthera pedata (Cucurbitaceae)

The highly specialized, two-celled hairs fringing the anthers ofCyclanthera pedata (L.)Schrad. and its relatives aid in pollination by producing a glue which sticks the coarse pollen grains onto insect visitors. This was proven by direct observations, confirming older assumptions. The adhesive is extruded from the big basal cell which bursts upon the slightest touch to the small top cell.—Turgor and, possibly, swelling pressure of the sticky material, are responsible for plasmoptysis and ejaculation. Cell contraction is due to tension of cuticular clips and, to a minor degree, to elasticity of the pectinic wall. A preformed apical dehiscence line disrupts when the top cell is bent aside.—The anthers hairs of a flower develop synchronously. From light and electron microscopic observations, the adhesive appears not to be a product of internal secretion. It originates from the endopolyploid giant nucleus of the basal cell, which finally degenerates by liquefying and swelling. The numerous peculiar elaioplasts apparently do not contribute to the hair's function.—The anther hairs are homologous to, and possibly have evolved from the so-called explosion hairs occurring on the green parts of manyCucurbitaceae.

Herrn Professor Dr.Walter Leinfellner zum 70. Geburtstag gewidmet.     

Calcium localization pattern in clover root hair cells associated with infection process: Studies with aureomycin

Summary Localized regions of calcium were shown to change in clover root hair cells after infection withRhizobium trifolii as shown with the Ca⁺⁺ binding antibiotic, chlorotetracycline. Some root hairs from the immature zone showed increased calcium fluorescence distributed through most of the cell. These root hair had a morphology with a notched side wall, typical of cells infected by bacteria. The maturing root hairs that show a growing infection thread or start of an infection thread, have a similar increased calcium fluorescence, especially around the area of origin of infection thread and tip of the root hair cell.Kettering contribution no. 722.     

Electrophysiological Responses to Fusaric Acid of Root Hairs from Seedlings of Date Palm-susceptible and -resistant to Fusarium oxysporum f. sp. albedinis

Bayoud, a vascular wilt of date palm caused by Fusarium oxysporum f. sp. albedinis (Foa), is the most devastating disease in palm groves of north Africa. Although Foa is able to induce resistance mechanisms in its host plant, no data are available on the early responses of the root cells. Fusaric acid (FA) is the main toxin found in culture filtrates from Foa aggressive strains. This phytotoxin induces modifications of membrane permeability or membrane potential in various cell types and could thus be involved in the early steps of signal exchange between the pathogen and the plant. We showed an early differential behaviour of the disease‐resistant and ‐susceptible cultivars from date palm when challenged by FA. This response could be due to a differential sensitivity of H⁺‐ATPases to FA.     

Polyphenol deposition in leaf hairs of Olea europaea (Oleaceae) and Quercus ilex (Fagaceae)

The subcellular localization (cytoplasm, vacuoles, cell walls) of polyphenol compounds during the development of the multicellular nonglandular leaf hairs of Olea europaea (scales) and Quercus ilex (stellates), was investigated. Hairs of all developmental stages were treated with specific inducers of polyphenol fluorescence, and the bright yellow-green fluorescence of individual hairs was monitored with epifluorescence microscopy. During the early ontogenetic stages, bright fluorescence was emitted from the cytoplasm of the cells composing the multicellular shield of the scales of O. europaea. Transmission electron micrographs of the same stages showed that these cells possessed poor vacuolation and thin cell walls. The nucleus of these cells may be protected against ultraviolet-B radiation damage. The progressive vacuolation that occurred during maturation was followed by a shifting of the bright green-yellow fluorescence from the perinuclear region and the cytoplasm to the cell walls. The same trends were observed during the development of the nonglandular stellate hairs of Quercus ilex, in which maturation was also accompanied by a considerable secondary thickening of the cell walls. Despite the differences in morphology, high concentrations of polyphenol compounds are initially located mainly in the cytoplasm of the developing nonglandular hairs, and their deposition on the cell walls takes place during the secondary cell wall thickening. These structural changes during the development of the leaf hairs make them a very effective barrier against abiotic (uv-B radiation) and probably biotic (pathogenic) stresses.     

Pollination mechanisms in sixCampanula species (Campanulaceae)

Pollination mechanisms within the genusCampanula were studied. Tests were undertaken to examine whether in vitro culture of pollen grains can serve as a useful tool for understanding the self- and cross-pollination mechanisms among species. Characteristics of pollen germination were interpreted in relation to mating system and floral biology. Four annual species (Campanula kremeri, C. dichotoma, C. afra, C. lusitanica), and two perennial species (C. rotundifolia andC. persicifolia) were investigated. In the annual species pollen germinability is controlled by (1) the age of pollen and/or (2) in what position pollen is deposited around the style. Correlations were found between pollen germinability and mating system in three of the four annual species. No correlations were found either between germinability and age of pollen or position on the style in the perennial species. Pollen germinability reached its maximum in the middle of the male phase in all species, except forC. dichotoma, which had a decreasing germinability throughout anthesis. The germinability was lowest at the time of stigma receptivity for all species except forC. persicifolia, where the stigma did not develop as long as pollen remained on the style. The pollen collecting hairs and pollen removal have been found to play an important role controlling the stigma development, thus affecting self-pollination. This was especially pronounced inC. persicifolia. Further studies will be undertaken to elucidate factors influencing pollination within the genusCampanula.     

Assessment of inequality of root hair density in Arabidopsis thaliana using the Gini coefficient: a close look at the effect of phosphorus and its interaction with ethylene

BACKGROUND AND AIMS: Root hair density (i.e. the number of root hairs per unit root length) in Arabidopsis thaliana varies among individual plants in response to different nutrient stresses. The degree of such variation, defined as inequality, serves as a unique indicator of the uniformity of response within a plant population to nutrient availability. METHODS: Using the Gini coefficient (G) as an inequality index, the inequality of root hair density in Arabidopsis thaliana 'Columbia' was evaluated under conditions of nutrient stresses; in particular the effect of phosphorus and its interaction with ethylene. KEY RESULTS: With decreasing phosphorus concentration, root hair density increased while inequality decreased logarithmically. The addition of the ethylene precursor 1-aminocyclopropane-1-carboxylate (ACC) under high phosphorus increased root hair density and decreased inequality by 7-fold. Inhibition of ethylene action with 1-methylcyclopropene (MCP) and silver thiosulphate (STS) under low phosphorus decreased root hair density, and increased inequality by 9-fold and 4-fold, respectively. The ethylene action inhibitors had little effect on root hair density under high phosphorus, but inequality increased 3-fold in the presence of MCP and decreased 2-fold in the presence of STS. Compared with the control, deficiencies in S, N and K increased inequality of root hair density, whereas deficiencies in P, Ca, B, Mn, Fe, Zn, Cu and Mg decreased inequality. In particular, the inequality of root hair density increased by over 2-fold under deficiencies of N or K, but decreased 14-fold under phosphorus deficiency. CONCLUSIONS: The inequality analysis indicates a strong correlation between prevalent signals from the environment (i.e. phosphorus stress) and the response of the plant, and the role of ethylene in this response. As the environmental signals become stronger, an increasing proportion of individuals respond, resulting in a decrease in variation in responsiveness among individual plants as indicated by reduced inequality.     

Growth and ultrastructure ofArabidopsis root hairs: therhd3 mutation alters vacuole enlargement and tip growth

The root hairs of plants are tubular projections of root epidermal cells and are suitable for investigating the control of cellular morphogenesis. In wild-typeArabidopsis thaliana (L.) Heynh, growing root hairs were found to exhibit cellular expansion limited to the apical end of the cell, a polarized distribution of organelles in the cytoplasm, and vesicles of several types located near the growing tip. Therhd3 mutant produces short and wavy root hairs with an average volume less than one-third of the wild-type hairs, indicating abnormal cell expansion. The mutant hairs display a striking reduction in vacuole size and a corresponding increase in the relative proportion of cytoplasm throughout hair development. Bead-labeling experiments and ultrastructural analyses indicate that the wavy-hair phenotype of the mutant is caused by asymmetric tip growth, possibly due to abnormally distributed vesicles in cortical areas flanking the hair tips. It is suggested that a major effect of therhd3 mutation is to inhibit vacuole enlargement which normally accompanies root hair cell expansion.