Effect of Spermidine and Methylglyoxal-bis (Guanyl-hydrazone) (MGBG) on In Vitro Pollen Germination and Tube Growth in Catharanthus roseus

Incorporation of polyamine-spermidine into the nutrient mediumat 10^–6 and 10^–5 M concentrations stimulates pollen-tubegrowth in vitro in Catharanthus roseus L. G. Don. MGBG, an inhibitorof spermidine biosynthesis, at 0.5 x 10^–3 and 1 x 10^–3M concentrations reduced the percentage of germination as wellas tube growth and at a concentration of 1.5 x 10^–3 Mgermination was totally inhibited. Pollen grains incubated inthe medium containing 1.5 x 10^–3 M MGBG, when transferredto a fresh medium with 10^–5 M spermidine, resulted in80% germination recovery, along with considerable tube growth.Experiments with actinomycin-D indicate that stimulation ofpollen-tube growth by spermidine may involve de novo synthesisof protein. Catharanthus roseus, pollen germination, tube growth, spermidine, MGBG, inhibition, actinomycin-D     

An Alginate Prill Formulation of Fusarium oxysporum Schlechtend: Fr. f. sp. erythroxyli for Biocontrol of Erythroxylum coca var. coca

A rice alginate prill formulation of isolate EN - 4 of Fusarium oxysporum f . sp . erythroxyli, pathogenic to Erythroxylum coca var . coca (coca) , was evaluated in greenhouse and field studies for its ability to enhance pathogen populations in the soil and cause disease in coca . The formulation was applied to four different soil types in the greenhouse at 33 . 6 kg ha 1 . It enhanced the population of EN - 4 in each soil and most ( > 90%) of the fungal population remained in the upper 5 cm of soil during the 49 - day experiment . When applied in field experiments , the formulation enhanced the population of EN - 4 in the soil . Isolate EN - 4 was present in the upper 7 . 6 cm of soil 28 days after application at populations similar to those in the greenhouse studies (1 103 to 1 104 colony - forming units (CFUs) / g of soil) . Elevated populations of the pathogen (1 102 CFUs / g of soil) were still present in treated soils 229 days after application of the formulation . The areas used for field studies were already infested with the pathogen and typically developed high levels of fusarium wilt within 2 years of planting with coca . The formulated F. oxysporum began having a significant effect on plant death 100 - 200 days after application based on repeated measures analysis . These data suggest that a formulation of F. oxysporum f . sp . erythroxyli which enhances the incidence of fusarium wilt in coca fields can be produced using established techniques .     

Effect of NaCl Salinity on Somatic Embryo Development in Sapindus trifoliatus L.

The effect of NaCl salinity on growth and development of somaticembryos of Sapindus trifoliatus L. was examined. Incorporationof 25 and 50 mol m^–3 NaCl into the medium greatly increasedthe growth and development of somatic embryos and both theseconcentrations favoured the production of secondary embryoids.However, supplementation of 100 mol m^–3 NaCl to the mediumdid not have any significant effect on the growth and developmentof somatic embryos. On the other hand, the culturing of proembryostructures in medium containing 200 mol m^–3 NaCl resultedin complete death within 7 d of salt exposure. Analysis of somatic embryos revealed that, upon salinization,they accumulated Na⁺ and Cl^– in significant amounts butthe content of Na⁺ was much less compared to that of Cl^–.Addition of NaCl (up to 50 mol m^–3) in the medium resultedin a considerable increase in the K⁺ content of somatic embryos.The content of proline in somatic embryos, however, increasedsubstantially in response to salinization. The amount of freesterols, steryl glycosides, steryl esters, and phospholipidsalso rose to higher values in salt-affected somatic embryos.The results suggest that somatic embryos of S. trifoliatus cantolerate concentrations of NaCl up to 100 mol m^–3 withoutaffecting growth and that they have sufficient cellular mechanismsto tolerate salinity at relatively high levels. Key words: Salinity, somatic embryo, sterols, phospholipids     

The Neural Network of the Limulus Retina: From Computer to Behavior

SYNOPSIS. The visual system of the horseshoe crab, Limulus polyphemus,provides an excellent opportunity for studying the neural basisof behavior. Quantitative analysis of the animal's visual behavioris now possible as is theoretical analysis of information processingin its retina. We combine these theoretical and behavioral approachesto investigate the nature of the signals the eye transmits tothe brain for the animal to see. Over the years theoretical studies of the Limulus eye were restrictedby the limited capabilities of single processor digital computers.However, a breakthrough in technology with the advent of parallelcomputers greatly enhances the analysis of large neural networkssuch as that of the retina. We have developed a time-dependentmodel of the Limulus retina on the Connection Machine (ModelCM-2), which is a massively parallel computer containing 32,768processors. The model represents a matrix of 64 x 128 receptorsand simulates interactions among receptors with digital filtersand transduction and adaptation within a receptor by a multistagecascade. Neural response patterns computed with the ConnectionMachine model replicate to a first approximation the patternsof neural activity recorded in the laboratory. Behavioral studies of Limulus vision carried out in the fieldcan be simulated on the Connection Machine. Neural responsesrecorded from behaving animals serve to test the accuracy ofthe model. Thus far we have developed just one model of theretina, but it eventually will have two forms, "daytime" and"nighttime," to account for the known circadian rhythms in retinalfunction. With a combination of field, physiological, and theoreticalstudies, we hope to gain a better understanding of the neuralmechanisms that underlie the animal's visually-guided behavior.     

Seed Surface Architecture and Random Amplified Polymorphic DNA Profiles of Paulownia fortunei, P. tomentosa and their Hybrid

The surface patterns of winged seeds of Paulownia fortunei,P. tomentosa and P. fortuneixP. tomentosa were examined by scanningelectron microscopy. The pattern of reticulation on the wingsand seed coat of P. fortunei and the hybrid are comparable,while that on P. tomentosa is different and more elongated.Also, the wings are more extended at the oblong ends of theseeds in the former when compared to the wings of P. tomentosa.Distinct random amplified polymorphic DNA (RAPD) patterns wereobtained for the three taxa and P. kawakamii with five differentrandom oligonucleotide primers, suggesting that the method canyield genetic markers for differentiating the taxa. Also, Southernblot analyses of the RAPD products of the hybrid and the twoparent species revealed shared (inherited) genetic polymorphisms.Copyright 1999 Annals of Botany Company Paulownia species and hybrid, seed surface architecture, reticulated thickening, RAPD markers, Scrophulariaceae.     

Dynamic secretion changes in the salt glands of the mangrove tree species Avicennia officinalis in response to a changing saline environment

The specialized salt glands on the epidermis of halophytic plants secrete excess salts from tissues by a mechanism that is poorly understood. We examined the salt glands as putative salt and water bi‐regulatory units that can respond swiftly to altering environmental cues. The tropical mangrove tree species (Avicennia officinalis) is able to grow under fluctuating salinities (0.7–50.0 dS m^?1) at intertidal zones, and its salt glands offer an excellent platform to investigate their dynamic responses under rapidly changing salinities. Utilizing a novel epidermal peel system, secretion profiles of hundreds of individual salt glands examined revealed that these glands could secrete when exposed to varying salinities. Notably, rhythmic fluctuations observed in secretion rates were reversibly inhibited by water channel (aquaporin) blocker, and two aquaporin genes (PIP and TIP) preferentially expressed in the salt gland cells were rapidly induced in response to increasing salt concentration. We propose that aquaporins are involved and contribute to the re‐absorption of water during salt removal in Avicennia officinalis salt glands. This constitutes an adaptive feature that contributes to salt balance of trees growing in saline environments where freshwater availability is limited.     

Bait shyness of two gerbils, Tatera indica indica Hardwicke and Meriones hurrianae Jerdon

Two rodents, Tatera indica indica Hardwicke and Meriones hurrianae Jerdon, developed aversion to zinc phosphide after one day's exposure to a sublethal dose. The poison shyness persisted for at least 115 and 35 days, respectively.