Communication in Plants: Comparison of Multiple Action Potential and Mechanosensitive Signals With Experiments.

Both action potentials and mechanosensitive signalling are an important communication mechanisms in plants. Considering an information-theoretic framework, this paper explores the effective range of multiple action potentials for a long chain of cells (i.e., up to 100) in different configurations, and introduces the study of multiple mechanosensitive activation signals (generated due to a mechanical stimulus) in plants. For both these signals, we find that the mutual information per cell and information propagation speed tends to increase up to a certain number of receiver cells. However, as the number of cells increase beyond 10 to 12, the mutual information per cell starts to decrease. To validate our model and results, we include an experimental verification of the theoretical model, using a PhytlSigns biosignal amplifier, allowing us to measure the magnitude of the voltage associated with the multiple AP's and mechanosensitive activation signals induced by different stimulus in plants. Experimental data is used to calculate the mutual information and information propagation speed, which is compared with corresponding numerical results. Since these signals are used for a variety of important tasks within the plant, understanding them may lead to new bioengineering methods for plants.

Electrical signal transmission in the plant-wide web.

Plants can communicate with other plants using wireless pathways in the plant-wide web. Some examples of these communication pathways are: (1) volatile organic compounds' emission and sensing; (2) mycorrhizal networks in the soil; (3) the plants' rhizosphere; (4) naturally grafting of roots of the same species; (5) electrostatic or electromagnetic interactions; and (6) acoustic communication. There is an additional pathway for electrical signal transmission between plants - electrical signal transmission between roots through the soil. To avoid the possibility of communication between plants using mechanisms (1)-(6), soils in pots with plants were connected by Ag/AgCl or platinum wires. Electrostimulation of Aloe vera, tomato, or cabbage plants induces electrotonic potentials transmission in the electro-stimulated plants as well as the plants located in different pots regardless if plants are the same or different types. The amplitude and sign of electrotonic potentials in electrostimulated and neighboring plants depend on the amplitude, rise, and fall of the applied voltage. Experimental results displayed cell-to-cell electrical coupling and the existence of electrical differentiators in plants. Electrostimulation by a sinusoidal wave induces an electrical response with a phase shift. Electrostimulation serves as an important tool for the evaluation of mechanisms of communication in the plant-wide web.

Dynamics of intracellular mannan and cell wall folding in the drought responses of succulent Aloe species.

Plants have evolved a multitude of adaptations to survive extreme conditions. Succulent plants have the capacity to tolerate periodically dry environments, due to their ability to retain water in a specialized tissue, termed hydrenchyma. Cell wall polysaccharides are important components of water storage in hydrenchyma cells. However, the role of the cell wall and its polysaccharide composition in relation to drought resistance of succulent plants are unknown. We investigate the drought response of leaf-succulent Aloe (Asphodelaceae) species using a combination of histological microscopy, quantification of water content, and comprehensive microarray polymer profiling. We observed a previously unreported mode of polysaccharide and cell wall structural dynamics triggered by water shortage. Microscopical analysis of the hydrenchyma cell walls revealed highly regular folding patterns indicative of predetermined cell wall mechanics in the remobilization of stored water and the possible role of homogalacturonan in this process. The in situ distribution of mannans in distinct intracellular compartments during drought, for storage, and apparent upregulation of pectins, imparting flexibility to the cell wall, facilitate elaborate cell wall folding during drought stress. We conclude that cell wall polysaccharide composition plays an important role in water storage and drought response in Aloe.

Electrotonic potentials in Aloe vera L.: Effects of intercellular and external electrodes arrangement.

Electrostimulation of plants can induce plant movements, activation of ion channels, ion transport, gene expression, enzymatic systems activation, electrical signaling, plant-cell damage, enhanced wound healing, and influence plant growth. Here we found that electrical networks in plant tissues have electrical differentiators. The amplitude of electrical responses decreases along a leaf and increases by decreasing the distance between polarizing Pt-electrodes. Intercellular Ag/AgCl electrodes inserted in a leaf and extracellular Ag/AgCl electrodes attached to the leaf surface were used to detect the electrotonic potential propagation along a leaf of Aloe vera. There is a difference in duration and amplitude of electrical potentials measured by electrodes inserted in a leaf and those attached to a leaf's surface. If the external reference electrode is located in the soil near the root, it changes the amplitude and duration of electrotonic potentials due to existence of additional resistance, capacitance, ion channels and ion pumps in the root. The information gained from this study can be used to elucidate extracellular and intercellular communication in the form of electrical signals within plants.

Contractile roots in succulent monocots: convergence, divergence and adaptation to limited rainfall.

Contractile roots (CRs) that pull shoots further down in the soil are a possible example of convergent evolution in two monocot families, the Agavaceae and the Asphodelaceae. The association between CRs, water uptake and habitat aridity was investigated for agaves, yuccas and aloes by assessing the occurrence of CRs and the amount of root contraction for glasshouse-grown plants with respect to mean annual rainfall of their native habitats. Structural features of CRs as well as root hydraulic conductance were compared with those of non-contractile roots (NCRs). CRs occurred in 55% of the 73 species examined, including 64% of the agaves and 85% of the yuccas, but in none of the aloes despite the occurrence of CRs in related genera. The phylogenetic distribution of CRs was consistent with multiple acquisitions or losses of the trait. The amount of root contraction showed a highly significant negative relationship with mean annual rainfall, although other environmental factors may also be important. Radial hydraulic conductance of the basal (contractile) zone exceeded that of the midroot zone for CRs; for NCRs, the opposite was true. Thus, CRs in the species examined may provide a mechanism for greater water uptake near the soil surface in regions with limited rainfall.

Genetic transformation of Aloe barbadensis Miller by Agrobacterium tumefaciens.

Despite the importance of aloe in cosmetic and pharmaceutical industries, improvement of aloe (Aloe barbadensis Miller) by genetic engineering was seldom reported previously. In this study, regeneration and transformation conditions, including explant selection and surface sterilization, use of different Agrobacterium strains, and co-culture processing, are optimized. The use of 20.0% sodium hypochloride (25 min) for sterilization was less detrimental to the health of explant than 0.1% mercuric chloride (10 min). Regeneration frequency from stems was much higher than that from leaves or sheaths. Explants were infected by Agrobacterium (30 min) in liquid co-cultural medium, and this was followed by three days co-culture on sterile filter papers with light for 10 h per day at 24 degrees C. Histochemical data demonstrated that the transient expression of GUS gene in the stem explants of aloe infected with Agrobacterium strains EHA105 and C58C1 was 80.0% and 30.0%, respectively, suggesting the higher sensitivity of the explants to EHA105 than to C58C1. Infected tissues were selected using G418 (10.0-25.0 mg/L) to generate transformants. Sixty-seven G418 resistant plantlets were generated from the infected explants. Southern blotting, PCR, and ELISA analyses indicated that the alien gene were successfully transferred into aloe and was expressed in the transgenic plants. This newly established transformation system could be used for the genetic improvement of aloe.

Inestabilidad cariológica durante la formación de células madres del polen en Aloe vera (Aloaceae)

Con el objetivo de esclarecer la posible existencia de anomalías citogenéticas que aminoren la fertilidad del polen de Aloe vera, se analizó la etapa de proliferación celular que lleva a la formación de células madres del polen (CMPs). Se recolectaron botones florales (BF) en 25 plantas de una población ubicada a 10°34’15’’ N, 64°12’08’’ W, los cuales fueron fijados en Carnoy I por 24 h y almacenados en etanol (70 % v/v). Las observaciones se realizaron en preparaciones temporales obtenidas por la tinción del contenido de las anteras suspendidas en orceína acética (1.5 % p/v) por 5 minutos. De las 9 411 células analizadas, 17 % mostraron 1-8 puentes entre cromátidas hermanas, 13 % 1-7 micronúcleos de 0.9-4.8 µm, 8.1 % estaban unidas por puentes y 0.1 % no contenían cromatina. El resto de las células (61.8 %) presentó configuraciones aparentemente normales y sin variaciones morfométricas. La proliferación irregular de una fracción de CMPs (39.2 %) sugiere que las condiciones ambientales de la zona árida donde se realizaron los muestreos inducen inestabilidad cromosómica y cambios fisiológicos que afectan el normal desarrollo de la mitosis premeiótica, generando pérdida o adición de fragmentos, asociados a deficiencias y duplicaciones génicas.

[Karyological instability during pollen mother cells formation in Aloe vera (Aloaceae)]. / Inestabilidad cariológica durante la formación de células madres del polen en Aloe vera (Aloaceae).

In order to clarify possible cytogenetic anomalies that reduce pollen fertility, premeiotic mitosis was studied in Aloe vera plants from a naturalized population in the northeast of Venezuela (10 degrees 34' 15" N and 64 degrees 12' 08" W). Karyological configurations were evaluated during the stage of cell proliferation leading to the formation of pollen mother cells (PMCs). The sampling was carried out in March 2005, choosing inflorescences without mechanical or biological damage from 25 plants selected at random. Flower buds (FB) 2 to 6 mm in length were collected from 7:00 AM through 6:00 PM, their perianths removed, and fixed in Carnoy I (3:1 ethanol/glacial acetic acid) for 24 h and stored in ethanol (70% v/v) until observation. Light microscope observations were done on temporary preparations obtained by overflowing anther content suspended in acetic orcein (1.5% w/v) for 5 min and softly squashing with the cover slip. A total of 9 411 cells were analyzed. Upper mitotic activity was observed in FB from 3.8 +/- 0.09 mm long, collected at 11:00 AM through 1:00 PM; 17% of PMCs showed one to eight sister chromatid bridges from anaphase to telophase; 13%, one to seven micronucleus of variable diameter (0.9 to 4.8 microm); 8.1% were united by thin chromatin filaments, and 0.1% lacked a nucleus. Other evaluated cells (61.8%) had apparently normal mitotic configurations, without considerable morphometric variations. The evident irregular proliferation of a PMCs fraction (39.2%) suggests that environmental stress conditions (day temperatures ranging 32.7 to 39.8 degrees C, high solar radiation and low humidity) induce chromosome instability and physiologic changes that affect the normal development during premeiotic mitosis. As a consequence, loss or addition of chromosome fragments can occur in association with deficiencies and gene duplications.

[Ultracytochemical studies of aloin in Aloe arborescens leaves].

Lead acetate precipitation method was used for ultracytochemical localization of aloin. The processes of aloin production, transport and storage were studied by transmission electron microscope. Results showed that aloin was produced in the plastids of the assimilating tissue. The aloin was transported through the plastid membrane to the surrounding endoplasmic reticulum and enveloped in the vesicles by the endoplasmic reticulum elements, the vesicles approached and later fused with the plasmalemma. Some vesicles of the plastid membrane directly fused with the plasmalemma. The vesicles released their contents into the apoplast through exocytosis, and finally reached the vascular bundle sheath by apoplastic translocation. Aloin was transported to the internal tangential wall of vascular bundle sheath cell through endoplasmic reticulum vesicles, and reached the cytoplasm of aloin cell by means of plasmodesmata. Finally, aloin was stored in the vacuoles of aloin cell.

Effect of ultrasonic exposure on Ca2+-ATPase activity in plasma membrane from Aloe arborescens callus cells.

We investigated the effect of ultrasound on plasma membrane (PM) Ca2+-ATPase activity of Aloe arborescens callus cells in solid culture. The calluses were exposed by a 20 kHz digital sonifier at the powers of 2 and 10 W from the effective exposure times of 2-10 s. PM Ca2+-ATPase activity was almost significantly higher at 2 W both in continuous wave and 10% duty cycle than that of the control (no ultrasound) at effective exposure times of 5 and 10 s. However, its activity decreased at 10 W in continuous wave exposure. It is possible that the PM Ca2+-ATPase configuration or structure may be partly damaged by high-energy ultrasound at 10 W. Our results showed that low-energy ultrasound exposure was a useful physical field to stimulate A. arborescens callus cells to adapt environmental stress through PM Ca2+-ATPase activity increase.

[Development of aloin cells and accumulation of anthraquinone in aloe leaf].

The development of aloin cells and its relationship with the accumulation of anthraquinone in aloe leaf were investigated with the methods of paraffin section, semi-thin section, histochemistry and fluorescent microscopy. The results showed: cells rounded the procambium bundle differentiated into bundle sheath at the initial stage of procambium bundle developing into vascular bundle. When the sieve tube members appeared in protophloem, there were a lay of procambium bundle cells reserved between the sieve tube members and bundle sheath. These cells began to devise, then developed into aloin cells through enlargement of volume and vacuolization with the differentiation of metaphloem and metaxylem. So the aloin cells were special phloem parenchyma cells because they shared the same origin with the other phloem cells. The investigation of histochemistry reflected that there were aloin precipitate in the central vacuole of aloin cells after the material was soaked in the liquid of 1% lead acetate [Pb (CH3COO)2]. In addition, the yellow fluorescence was observed in aloin cells when the section of fresh material was investigated under the fluorescent microscope with blue light, which suggested the aloin cells of vascular bundles were the mainly storage site of anthraquinone.

Aloe L.--a second plant family without (TTTAGGG)n telomeres.

The physical ends of chromosomes are protected and stabilised by telomeres. The sequence of telomeric DNA normally consists of a simple repeating unit that is conserved in many organisms. Most plants examined have been shown to possess Arabidopsis-type telomeres consisting of many repeat copies of the sequence 5'-TTTAGGG-3'. Using fluorescent in situ hybridisation, slot blotting and the asymmetric polymerase chain reaction we demonstrate an absence of Arabidopsis-type telomeres in the genus Aloe (family Asphodelaceae). The only other plant genera so far reported without such telomeres are Allium, Nothoscordum, and Tulbaghia (family Alliaceae). As these genera and Aloe are petaloid monocots in the Asparagales, it is suggested that an absence of Arabidopsis-type telomeres may be characteristic of this related group of plants.