The Effects of Gibberellins on the Growth of Excised Tomato Roots

1. At appropriate concentrations both gibberellic acid (GA) and1-naphthalene-acetic acid (NAA) enhance the main axis growthof excised tomato roots grown in culture media containing sucroseat concentrations below 1 per cent. Lateral root extension growthis enhanced by GA at all sucrose concentrations tested; onlyat the lower sucrose concentrations is this effect observedwith NAA. Both GA and NAA increase the number of emergent lateralroots and this effect is most marked in media of low sucrosecontent. Both GA and NAA at higher concentrations inhibit rootgrowth but NAA exhibits its full range of growth effects overa much narrower concentration range than GA.
2. GA, like NAA,speeds up the loss of meristematic activity whichoccurs whenindividual meristems are repeatedly subculturedin media containing1 per cent, or higher concentrations ofsucrose.
3. The promotionof main axis growth by both GA and NAA involvesenhanced cellelongation and cell division. At a moderatelyinhibitory concentrationGA reduces both cell elongation andcell division; this is notthe case with NAA.
4. Gibberellins A₁, A₂, and A₄ resemble GA(gibberellin A₃) intheir growth effects. Allogibberic acidlike G A promotes lateralroot extension growth but causes markedinhibition of root growthat a much lower concentration thanGA.

     

Monitoring Golden-Cheeked Warblers on Private Lands in Texas

ABSTRACT A majority of North American breeding habitat for neotropical migrants exists on private lands, requiring monitoring strategies focused on habitat in these private holdings. We outline study designs and protocols using repeated Presence-Absence surveys across a gradient of patch sizes to develop a range-wide monitoring program for the endangered golden-cheeked warbler (Dendroica chrysoparia) in Texas, USA. We surveyed 200–400 point-count locations across approximately 30 private properties annually from 2005 to 2008. We used data from our surveyed patches (n = 147) and the Ψ (occupancy), p (detection), and γ = 1 - ɛ parameterization to estimate patch dynamics and associated detection probabilities for golden-cheeked warblers. Patch size had a strong association with patch occupancy, and all patches >160 ha were predicted to be occupied. We found no evidence that large golden-cheeked warbler populations located on public lands in the vicinity of our study area influenced occupancy dynamics. We conducted simulations across a range of detection probabilities to evaluate potential sample sizes for both standard- and removal-based occupancy modeling. Simulations using parameter estimates from our analysis indicated that removal-based sampling is superior to standard sampling. Based on our results, surveying golden-cheeked warbler presence in oak-juniper (Quercus-Juniperus) patches under a removal modeling framework should be considered as one alternative for range-wide monitoring programs because patch-level monitoring would be necessary to estimate proportion of range occupied. Large contiguous patches are rare across the species’ range; hence, conservation and management of the mosaic of smaller patches within a landscape context would be required for maintaining species viability. Thus, we recommend the identification of areas where smaller, contiguous patches represent a significant portion of the available habitat within the local landscape and targeting these areas for habitat maintenance and improvement.     

Conspecific Attraction is a Missing Component in Wildlife Habitat Modeling

Abstract Wildlife biologists use knowledge about wildlife-habitat relationships to create habitat models to predict species occurrence across a landscape. Researchers attribute limitations in predictive ability of a habitat model to data deficiencies, missing parameters, error introduced by specifications of the statistical model, and natural variation. Few wildlife biologists, however, have incorporated intra- and interspecific interactions (e.g., conspecific attraction, competition, predator-prey relationships) to increase predictive accuracy of habitat models. Based on our literature review and preliminary data analysis, conspecific attraction can be a primary factor influencing habitat selection in wildlife. Conspecific attraction can lead to clustered distributions of wildlife within available habitat, reducing the predictive ability of habitat models based on vegetative and geographic parameters alone. We suggest wildlife biologists consider incorporating a parameter in habitat models for the clustered distribution of individuals within available habitat and investigate the mechanisms leading to clustered distributions of species, especially conspecific attraction.     

Site-directed monoclonal antibodies against the amino terminus of 124-kDa phytochrome from Avena sativa L.

Abstract Two monoclonal antibodies (AFRC MAC 184 and 185) have been raised in rats against a synthetic octadecapeptide corresponding to the N-terminus of Avena phytochrome. The peptide was conjugated to tuberculin purified protein derivative (PPD) for immunization and the cell lines screened by ELISA using the free peptide. Both antibodies bind to intact 124-kDa phytochrome on Western blots and in a double antibody sandwich ELISA. In the ELISA, they have an approximately four-fold higher affinity for Pr than Pfr. Conformational changes during photoconversion, therefore, involve the extreme N-terminus of the phytochrome molecule.     

An Analysis of Seed Development in Pisum sativum: VIII. DOES ABSCISIC ACID PREVENT PRECOCIOUS GERMINATION AND CONTROL STORAGE PROTEIN SYNTHESIS?

The influence of abscisic acid (ABA) on the precocious germinationand storage protein production of pea seeds has been examinedusing embryo and pod culture. The precocious germination ofembryos in culture could not be inhibited fully by ABA on apermissive medium (2% sucrose) even at 0.1 mol m^–3. However,increasing the sucrose concentration to 5% caused near completeinhibition when ABA was added to the medium. Embryos of differentweights cultured on a high osmoticum (mannitol-containing medium),equivalent to 10% sucrose, did not show any consistent differencein ABA content. When fluridone was added to a non-permissiveculture medium, no decrease in ABA content of the embryos couldbe observed and no precocious germination was induced. In contrast,fluridone was able to prevent the accumulation of ABA in seedspresent in pods cultured in its presence from an early stageof development. These seeds, however, grew normally and reachedmaturity, did not germinate precociously in vivo, were desiccationtolerant and still produced storage protein message whetheror not ABA was included in the culture medium. It does not appear,therefore, that ABA regulates normal development or storageprotein synthesis in pea embryos. Key words: Abscisic acid, peas, Pisum sativum, seed development     

Gibberellins and the Growth of Excised Tomato Roots: Comparison of gib-1 Mutant and Wild Type and Responses to Applied GA3 and 2S, 3S Paclobutrazol

Clones of excised roots of wild type tomato (Lycopersicon esculentum,Mill., cv. Moneymaker) and a near-isogenic GA-deficient mutant(gib-1/gib-1) were cultured in modified White's medium containing1.5% w/v sucrose. The linear elongation rate of the main axisof the gib-1 mutant was 40% less than that of the wild type.In addition, the main axis of the gib-1 mutant was thicker thanthat of the wild type but main axis volume growth was the samein both genotypes, indicating that the gib-1 allele was affectingthe orientation of root expansion. There was no evidence tosuggest that the gib-1 allele affected either the pattern ofemergence or the density of lateral roots. Elongation rate andthickness of gib-1 mutant roots were restored to those of thewild type by the addition of low concentrations (0.1–1.0µM) of gibberellic acid (GA3). These concentrations ofGA3 caused a slight reduction in extension growth of wild typeroots, indicating that endogenous GAs were not limiting elongationof normal roots in culture. The GA biosynthesis inhibitor, 2S,3S paclobutrazol, at 0.1 µM, significantly reduced elongationof wild type roots and this inhibition was counteracted by 0.1µM GA₃. It is concluded that the difference in growthbetween the gib-1 mutant and the wild type represented GA-dependentgrowth. Low concentrations of 2S, 3S paclobutrazol caused onlya small (5%) reduction in growth of the gib-1 mutant and thisgrowth inhibition was not reversed by GA₃. This observation,and the fact that gib-1 mutant roots grow in the absence ofadded GA₃, suggested that part of root growth was GA-independent.However, the possibilities that the gib-1 mutant is ‘leaky’and that paclobutrazol does not inhibit GA biosynthesis completelycannot be excluded. Key words: gib-1 mutant, gibberellic acid, Lycopersicon esculentum, 2S, 3S paclobutrazol, root growth     

The Effects of Priming and 'Natural' Differences in Quality amongst Onion Seed Lots on the Response of the Rate of Germination to Temperature and the Identification of the Characteristics under Genotypic Control

Ellis, R. H. and Butcher, P. D. 1988. The effects of primingand ‘natural’ differences in quality amongst onionseed lots on the response of the rate of germination to temperatureand the identification of the characteristics under genotypiccontrol —J. exp. Bot. 39: 935–950. A screening procedure was applied to define the response ofthe rate of seed germination to sub-and supra-optimal temperaturesfor different lots or sub-lots of two onion (Allium cepa L.)cultivars.Three sub-lots of the cultivar White Lisbon were derived froma control lot by osmotic priming (–1.4 MPa, 20 °C.7 d) alone, by priming and drying and by priming, drying andsubsequently storing the seeds for 7 weeks at 2–5 °C.The major effect of priming was to reduce the thermal time forgermination at both sub- and supra-optimal temperatures. Primingalone also altered the distribution of thermal times at sub-optimaltemperatures. A new equation is presented to describe this variation.In contrast, priming had no consistent effect on base temperature(T_b and little effect on the distribution of ceiling temperatures[T_e(G)]. For the control lot of White Lisbon T_b was 4°C,whilst the best common estimate of T_b for all four sub-lotswas 3.5°C. The mean estimate of T_c(50) for the control,primed and primed and dried sub-lots was 35.5°C.Comparisonof three lots of the cultivar Senshyu Semi Globe Yellow of widely-differingviability showed substantial differences in the thermal timefor germination at sub-optimal temperatures, but no significantdifferences in T_b (P>0.10), the common estimate being 4°C.There was a significant negative correlation between probitpercentage viability and the logarithm of the thermal time for50% germination at sub-optimal temperatures amongst the threelots (P<0.05). The work suggests that base temperature forgermination is a genotypic characteristic which is unaffectedby differences in seed quality. It also shows that the effectof priming, quantified as a reduction in thermal time requirementsfor germination, varies amongst the seeds within a lot. Key words: -Onion, seed germination rate, temperature, priming     

Persistent Controversy in Statistical Approaches in Wildlife Sciences: A Perspective of Students

ABSTRACT The controversy over the use of null hypothesis statistical testing (NHST) has persisted for decades, yet NHST remains the most widely used statistical approach in wildlife sciences and ecology. A disconnect exists between those opposing NHST and many wildlife scientists and ecologists who conduct and publish research. This disconnect causes confusion and frustration on the part of students. We, as students, offer our perspective on how this issue may be addressed. Our objective is to encourage academic institutions and advisors of undergraduate and graduate students to introduce students to various statistical approaches so we can make well-informed decisions on the appropriate use of statistical tools in wildlife and ecological research projects. We propose an academic course that introduces students to various statistical approaches (e.g., Bayesian, frequentist, Fisherian, information theory) to build a foundation for critical thinking in applying statistics. We encourage academic advisors to become familiar with the statistical approaches available to wildlife scientists and ecologists and thus decrease bias towards one approach. Null hypothesis statistical testing is likely to persist as the most common statistical analysis tool in wildlife science until academic institutions and student advisors change their approach and emphasize a wider range of statistical methods.     

The Conversion of 3-Indolylmethylglucosinolate to 3-Indolylacetonitrile by Myrosinase, and its Relevance to the Clubroot Disease of the Cruciferae

[Methylene-¹⁴C]-3-indolylmethylglucosinolate (¹⁴C-IMG) was convertedin vitro to [methylene-¹⁴Cl-3-indolylacetonitrile (¹⁴C-IAN)by myrosinase over a pH range of 4.0-6.0 and this conversionwas enhanced by ferrous ions. Other products of the reactionincluded 3-indolylmethanol, 3, 3'-diindolylmethane and ascorbigenA. Trace amounts of ¹⁴C-IAN were produced non-enzymically from¹⁴C-IMG in the presence of ferrous ion over a similar _pH range.Furthermore, swede tissues (Brassica napus cv. Danestone) infectedwith Plasmodiophora brassicae Woron. could convert ¹⁴C-IMG to¹⁴C-IAN. These results were consistent with the hypothesis thatthe overgrowth symptoms of the clubroot disease are caused bythe conversion of IMG to the auxin precursor IAN.     

An Investigation of Factors which Influence the Production of Abnormal Terpenoids by Callus Cultures of Andrographis paniculata Nees

Callus and suspension cultures of Andrographis paniculata havebeen shown to produce three new sesquiterpene lactones whichhave been named paniculides. A, B, and C and not the andrographolides(diterpenes) produced by the intact plant. Cultures derived from leaves, stems, hypocotyls, roots, andembryos accumulated paniculides, but no andrographolides weredetected. Conversely andrographolides, but no paniculides weredetected in extracts from leaves, stems and roots of intactseedlings. Modifications of the medium including the use of different syntheticauxins and the replacement of coconut milk with kinetin andcasein hydrolysate did not influence paniculide production bythe hypocotyl cultures. In addition an established root isolatecultured for 9 months on a simple synthetic medium without auxin,meso-inositol or coconut milk still synthesized significantquantities of paniculides. Diurnal fluctuations of temperature and light did not influencethe pattern of compounds produced although cultures grown incomplete darkness produced the individual paniculides in differentproportions. Possible explanations for these findings are discussed.