bluuebunny/crossref_metadata_2025 huggingface dataset:
The Substitutability of Real Estate Assets
Authors: Seck Diery
Published: September 2003

This paper investigates the degree of substitutability between securitized real estate assets and real estate assets whose prices are appraisal‐based. Given the insensitivity of unsecuritized asset's returns to the returns on stock market indices, equilibrium asset pricing models cannot be used to compare these two avenues of investment. Two assets are deemed substitutable if the information sets underlying unbiased, minimum error variance estimates of their pricing parameters are identical. The empirical evidence shows that the prices of the transactions‐based assets—real estate investment trusts and the stock price index of the home building industry—follow a random walk while the prices of the appraisal‐based assets—FRC/NCREIF indices—do not. The variance decompositions of the vector autoregressions also show that the level of economic activity helps predict the price indices of appraisal‐based assets while the stock market index and the term structure of interest rates are better predictors of the prices of transactions‐based assets
The Dynamic Impact of Unseasonable Weather on Construction Activity
Authors: Coulson N. Edward , Richard Christian
Published: September 2003

We simulate the effects of unseasonable increases in temperature and precipitation on housing starts and completions in each of the four Census regions. Using an overidentified vector autoregression model the dynamics of housing starts and completions are estimated. The persistence of housing activity over time implies that weather shocks also have long‐lasting effects, though the impact seems large only in the North Central region.
The Role of Principal‐Agent Conflicts in the 1980s Thrift Crisis
Authors: Cole Rebel A. , Eisenbeis Robert A.
Published: September 2003

Agency theory suggests that many of the costs incurred by the taxpayer during the 1980s thrift crisis were the result of conflicts between principals and their agents. This study models the costs associated with three distinct types of agency conflicts involved in closing an insolvent thrift—conflicts between creditors and owners, between owners and managers, and between taxpayers and government officials. Using a model that controls for sample‐selection bias, the study presents strong evidence that thrift owners effected wealth transfers from creditors by undertaking high‐risk investments, and that government officials pursued policies that increased losses to the thrift deposit insurance fund which ultimately were funded by the taxpayer. The results do not show that managers effected wealth transfers from owners through expense‐preference behavior, but rather that inefficient management increased the losses of the deposit insurance fund.
Explaining Intermetropolitan Variation in Housing Prices, Rents and Land Prices
Authors: Potepan Michael J.
Published: September 2003

In attempting to explain why housing prices, rents and urban land prices vary so dramatically between U.S. metropolitan areas, a simple model of a metropolitan housing market is presented identifying three interrelated submarkets. Estimating equations for rent, housing prices and urban land prices are identified and estimated using two‐stage least squares. The empirical results provide strong support for the theoretical model concerning how these three submarkets interact. The results also suggest that household income and construction costs are the most important factors causing housing prices, rents and land prices to vary between metropolitan areas.
Search and Liquidity in Single‐Family Housing
Authors: Forgey Fred A. , Rutherford Ronald C. , Springer Thomas M.
Published: September 2003

A two‐stage least squares model of housing prices is estimated with data collected from 3358 single‐family home transactions. The results provide evidence for an optimal marketing period and indicate that a liquidity premium is priced in single‐family home sales. Consistent with the hypothesis derived from economic search models, the model shows higher selling prices for houses having longer expected marketing periods. The model also shows a price premium for houses that sell faster than expectations. This effect supports the concept that liquidity is a value‐enhancing characteristic.
Mixed Uses and the Redevelopment Option
Authors: Childs Paul D. , Riddiough Timothy J. , Triantis Alexander J.
Published: September 2003

This paper considers how the potential for mixing uses and redevelopment impact property value. Operating flexibility of this type is found to significantly increase property value when the correlation between payouts from different property types is low or when redevelopment costs are low. The ability to mix uses and redevelop over time is also shown to affect the timing of initial land development. The shape of the development boundary is shown to differ considerably depending on whether marginal revenue is constant or decreasing to scale. Both policy and empirical implications concerning the effects of multiple‐use zoning are discussed.
Adjustable and Fixed Rate Mortgage Termination, Option Values and Local Market Conditions: An Empirical Analysis
Authors: VanderHoff James
Published: September 2003

This paper analyzes the probabilities of prepayment or default for Fixed Rate Mortgages (FRMs) and Adjustable Rate Mortgages (ARMs). Using data from the period 1985–1992, the analysis indicates that the likelihood of prepayment of thirty year FRMs was determined primarily by house price appreciation and personal income growth and the likelihood of prepayment of fifteen year FRMs was determined primarily by interest rate changes. ARMs were prepaid less frequently than FRMs, were less likely to be prepaid when interest rates declined and defaulted more often than FRMs. The analysis provides evidence that ARM holders are less mobile than FRM holders.
Turnover as a Measure of Demand for Existing Homes
Authors: Berkovec James A. , Goodman John L.
Published: September 2003

Changes in the turnover of existing homes are often equated with changes in housing demand, but it is not clear if, or why, this linkage exists. This paper documents the positive correlation between changes in turnover and changes in housing demand and develops a search model that explain the linkage. One implication of the analysis is that, for high frequency data, turnover is superior to price as an indicator of change in housing demand.
Rational Expectations, Market Fundamentals and Housing Price Volatility
Authors: Clayton Jim
Published: September 2003

This paper derives a forward‐looking rational expectations house price model and empirically tests its ability to explain short‐run fluctuations in real house prices. A novel approach to proxying the imputed rents of owner‐occupied housing, as a function of observable housing market fundamentals, is combined with a housing market arbitrage relation to derive a present value model for real house prices. Tests of the rational expectations, nonlinear cross‐equation restrictions reject the joint null hypothesis of rational expectations and the asset‐based housing price model for quarterly, single‐detached house prices in the city of Vancouver, British Columbia from 1979–1991. The model fails to fully capture observed house price dynamics in two real estate booms but tracks real house prices well in less volatile times, suggesting that prices may temporarily deviate from fundamental values in real estate price cycles.
Forecasting the Discounts of Market Prices from Appraised Values for Real Estate Limited Partnerships
Authors: Barber Brad M.
Published: September 2003

A vexing problem for the appraisal industry has been estimating an appropriate discount for the value of real estate limited partnerships (RELPs) relative to their appraised value. This research develops a linear regression model that explains over 80% of the cross‐sectional variation in discounts across 60 RELPs using characteristics of each partnership. Among a holdout sample of 41 RELPs, the model provides forecasts of discounts that are superior to assuming no discount or applying a mean discount to all partnerships. Discounts are greatest for RELPs with low current yields, low leverage and high trading ranges for their market prices.
Systematic Risk and Diversification in the Equity REIT Market
Authors: Gyourko Joseph , Nelling Edward
Published: September 2003

This paper employs stock market‐based data to examine the systematic risk and diversification properties of publicly traded equity real estate investment trusts (REITs). A unique data sample is created by combining firm return data with information on their property type holdings and the location of their investments. The systematic risk of equity REITs appears to vary by the type of property in which they invest, with beta being significantly higher for retail‐oriented REITs than for REITs owning industrial and warehouse properties. In addition, the stock market data provides no evidence that REIT diversification across property types or broad geographic regions actually results in meaningful diversification as reflected in a standard market‐based measure—the R2 from a simple market model regression.
A Comparison of Prices Brought by English Auctions and Private Negotiations
Authors: Lusht Kenneth M.
Published: September 2003

A comparison of house prices brought by English auctions and private negotiations produced evidence that the pricing mechanism matters. In an active market for middle‐ to high‐priced houses, auctions extracted higher prices than private negotiations.
A Note on Ranking Real Estate Research Journals
Authors: Diaz Julian , Black Roy T. , Rabianski Joseph
Published: September 2003

An understanding of how thirty real estate journals are perceived for promotion and tenure and for professional applicability was sought by surveying members of the two most important real estate academic organizations. Several subgroup comparisons were made revealing some common perceptions but a significant amount of disagreement as well. Among findings robust across the surveyed community were that the Journal of the American Real Estate and Urban Economics Association (changed to Real Estate Economics in 1995) is the most important outlet for promotion and tenure and the Appraisal Journal is the most important outlet for professional applicability. Two distinct journal groupings emerged: an academic group composed of eight journals and a professional group of twenty.
Housing and Urban Development Indicators: A Good Idea Whose Time Has Returned
Authors: Malpezzi Stephen , Mayo Stephen K.
Published: September 2003

This special issue of Real Estate Economics is devoted to “Housing and Urban Development Indicators.” The issue has been underwritten by the United States Department of Housing and Urban Development as a U.S. Contribution to the United Nation's Habitat II Conference, held in Istanbul, Turkey in June 1996. This introduction first briefly explains the role of indicators in urban research. Current research on indicators is then described, including a major international research effort undertaken in over fifty countries with support from numerous academics and other researchers, the United Nations, the World Bank and a number of governments. Finally, the papers in this issue are introduced and placed in context.
Indicators of Local Housing Affordability: Comparative and Spatial Approaches
Authors: Bogdon Amy S. , Can Ayse
Published: September 2003

This paper focuses on the measurement of local housing affordability problems. A number of different housing market indicators are offered that help identify the magnitude and nature of housing affordability problems and their geographic distribution. This interest is prompted by the predominance of housing affordability problems and the severity of the problems for many of the lowest income renter households. In addition, there is significant policy interest in “the national goal that every American family be able to afford a decent home in a suitable environment” (National Affordable Housing Act of 1990). This paper develops measures of the spatial distribution of affordability problems and implements measures of the mismatch between the demand and supply of housing affordable to the lowest income households.
Indicators of Housing Finance Intergenerational Wealth Transfers
Authors: Deutsch Edwin
Published: September 2003

This paper sheds light on intrafamilial gifts for housing. By using Austrian intergenerational survey data various questions are addressed. First, is familial aid more or less widespread in given social strata? Second, what are the determinants and motives for family gifts? And third, what are the possible impacts on the choice set of their recipients? Probit estimates show that gifts significantly depend on the parents lifetime financial position, consistent with life cycle permanent income (LCPI) approaches. Gifts to remove liquidity constraints are more difficult to reconcile with LCPI. “Dynastic” gifts that support household formation and ownership acquisition may be interpreted as intergenerational exchange. They occur more frequently than periodical cash transfers where altruistic behavior cannot be ruled out.
A Long Run House Price Index: TheHerengracht Index, 1628–1973
Authors: Eichholtz Piet M.A.
Published: September 2003

This article introduces a biennial historic index of real estate values for the period 1628 through 1973. This index is based on the transactions of the buildings on the Herengracht, one of the canals in Amsterdam. Since its development, the quality of the buildings on this canal has been on a constant, high level, which makes the Herengracht a unique sample to base a long run house price index upon. The index is a hedonic repeated‐measures index and is estimated in real terms. An index is also constructed in nominal terms. The average real price increase after World War II is about 3.2% per annum. Nevertheless, the real value of the index in 1973 is only twice as high as it was in 1628.
International Evidence on Real Estate Securities as an Inflation Hedge
Authors: Liu Crocker H. , Hartzell David J. , Hoesli Martin E.
Published: September 2003

The current study investigates whether real estate securities continue to act as a perverse inflation hedge in foreign countries given security design differences. Both a stationary and a nonstationary risk free rate are alternatively used in conjunction with the methodology of Fama and Schwert (1977) and also the methodology of Geske and Roll (1983) to investigate this question. Real estate securities provide a worse hedge against inflation relative to common stocks in some countries and are comparable to stocks in other countries. Also, evidence supports the reverse causality model of Geske‐Roll.
Follow the Leader: How Changes in Residential and Non‐residential Investment Predict Changes in GDP
Authors: Green Richard K.
Published: September 2003

This paper examines the effect of different kinds of investments on the business cycle. Specifically, it examines whether residential and non‐residential investment Granger cause GDP, and whether GDP Granger causes each of these types of investments. The paper uses quarterly National Income and Products Data for the period 1959 to 1992. Under a wide variety of time‐series specifications, residential investment causes, but is not caused by GDP, while non‐residential investment does not cause, but is caused by GDP. Thus, housing leads and other types of investment lag the business cycle. The results also suggest that policies designed to funnel capital away from housing into plant and equipment could produce severe short‐run dislocations.
An Analysis of Resolution Trust Corporation Transactions: Auction Market Process and Pricing
Authors: Nanda Sudhir , Owers James E. , Rogers Ronald C.
Published: September 2003

This article describes the operations of the Resolution Trust Corporation (RTC), examines the procedures it employs to resolve distressed Savings and Loan scenarios and investigates the pricing of transactions undertaken by the RTC. The RTC has been criticized for allegedly transferring properties to acquirers at “bargain” prices. The transactions involving publicly traded acquirers in RTC sales are examined from an auction theory perspective. Overall, there is little evidence that winning bidders experience stock price gains. There are, however, subsets of bidders for which the outcomes are predominantly negative. The only category of transactions which provide statistically significant gains to acquirers are Insured Deposit Transfers.
The Stock Performance of Securitized Real Estate and Master Limited Partnerships
Authors: Wang Ko , Erickson John
Published: September 2003

This paper examines the stock performance of 144 master limited partnerships (MLPs) holding real estate and other types of assets. MLP stocks were found to underperform the market on a risk‐adjusted basis during the period 1981–1991. The evidence indicates that the MLP organizational form has not been a superior vehicle for holding real estate. Also, the performance of real estate MLP stocks is similar to the performance of the stocks of other types of MLPs and that of real estate MLP stock performance is comparable to the performance of real estate investment trust stocks.
Do Common Risk Factors in the Returns on Stocks and Bonds Explain Returns on REITs?
Authors: Peterson James D. , Hsieh Cheng‐Ho
Published: September 2003

The monthly returns on equity and mortgage real estate investment trusts (REITs) are analyzed over the period July 1976 to December 1992. The results indicate that risk premiums on equity REITs are significantly related to risk premiums on a market portfolio of stocks as well as to the returns on mimicking portfolios for size and book‐to‐market equity factors in common stock returns. Mortgage REIT risk premiums are significantly related to the three stock market factors and two bond market factors in returns. Also, mortgage REIT shares underperform by an average of 6.8% per year.
Estimating Borrower Mobility from Observed Prepayments
Authors: Harding John P.
Published: September 2003

This article describes a method used to estimate parameters describing the mobility of borrowers choosing fixed‐rate mortgages. Using a mortgage valuation model that predicts prepayments contingent upon parameters describing the distribution of expected tenure in the home, the average mobility of borrowers can be estimated from observed prepayment behavior. This article estimates the mobility of borrowers who chose fixed‐rate mortgages before 1980 and borrowers who chose similar mortgages in the second half of the 1980s, when adjustable‐rate mortgages were widely available. The empirical results support the claim that the average mobility of fixed‐rate borrowers has declined.
The Impact of Initial‐Year Discounts on ARM Prepayments
Authors: Green Richard K. , Shilling James D.
Published: September 2003

This study uses new data on the rate of prepayment on conventional single‐family adjustable‐rate mortgages (ARMs) that originated between 1983 and 1986 to determine if ARMs with and without initial‐year discounts have the same probability of paying off. The new data are from a large national private mortgage insurer in the United States. Each loan is tracked from its origination date through prepayment or the end of 1991. Nonparametric test statistics are used to test for differences in these prepayment rates. The findings suggest that ARMs with initial‐year discounts are paid off at a rate that is essentially no different from the rate on otherwise comparable ARMs without initial‐year discounts.
Redevelopment of Real Assets
Authors: Williams Joseph T.
Published: September 2003

Real assets can be redeveloped repeatedly. Unlike financial assets, the option to redevelop real assets can be exercised infinitely often. For a depreciating real asset, the optimal exercise policy and resulting market values are calculated analytically and compared to the standard solution with at most one redevelopment. Relative to the standard solution, redevelopment is on average more frequent and less extensive, and the resulting market values are greater.
Congestion Effects of Spatial Growth Restrictions: A Model and Empirical Analysis
Authors: Cho Man
Published: September 2003

The present study characterizes the congestion effect of spatially designated growth controls, such as greenbelt or urban growth boundaries. The developed model demonstrates that the congestion externality caused by a binding growth restriction can understate total welfare costs of the regulation but overstate the amount of welfare transfer from renters of urban land to landowners. This article also examines costs and benefits of different development options given a binding growth restriction, and shows that non‐consideration of the congestion externality is likely to skew choice toward high‐density development. To test the hypothesized regulatory effect, a pooled time‐series and cross‐sectional analysis is performed with the land price data from Seoul, Korea. The results offer evidence of the gradient‐flattening effect of the greenbelt regulation in the study area.
The Value of Federal Sponsorship: The Case of Freddie Mac
Authors: Gatti James F. , Spahr Ronald W.
Published: September 2003

The Federal Housing Enterprises Financial Safety and Soundness Act of 1992 attempts to limit the risk borne by the taxpayer due to federal sponsorship of the Federal Home Loan Mortgage Corporation (FHLMC) and the Federal National Mortgage Association by: (1) controlling their range of activities; (2) requiring a level of capital sufficient to absorb substantial losses; and (3) providing a mechanism for closure if capital is insufficient. This article estimates the impact of the capital standards on the value to the FHLMC of federal sponsorship. Although FHLMC's level of capital exceeds requirements, the federal government still bears a nontrivial portion of the FHLMC's risk.
Using Nonlinear Tests to Examine Integration Between Real Estate and Stock Markets
Authors: Okunev John , Wilson Patrick J.
Published: September 2003

An alternative approach to test whether the real estate and stock markets are cointegrated is presented. A nonlinear test, which allows for a stochastic trend term as opposed to a deterministic drift term, is developed. The results of the nonlinear model are compared to the results obtained using conventional cointegration tests. The cointegration results support the view that the real estate and stock markets are segmented, whereas the nonlinear model supports the view that the markets are fractionally integrated. There is a nonlinear relationship between the stock and real estate markets, but movement of the real estate market towards the stock market is slow and divergence between the two markets can be prolonged.
Real Estate and the Arbitrage Pricing Theory: Macrovariables vs. Derived Factors
Authors: Chen Su‐Jane , Hsieh Cheng‐Ho , Jordan Bradford D.
Published: September 2003

Two empirical models are used to implement the arbitrage pricing theory: the factor loading model (FLM) and the macrovariable model (MVM). This study compares the ability of these two models to explain real estate returns using equity REIT returns as a proxy. Two tests are performed: a comparison of crosssectional adjusted‐R2's and the Davidson and Mackinnon test. The results show that while the two models perform equally well during the period 1974–1979, the MVM outperforms the FLM over the periods 1980–1985 and 1986–1991. In addition, both models suggest superior financial performance for EREITs relative to other investments in the market during the period 1980–1985.
Temporal and Spatial Information Diffusion in Real Estate Price Changes and Variances
Authors: Dolde Walter , Tirtiroglu Dogan
Published: September 2003

This article examines patterns of temporal and spatial diffusion of real estate price changes. In addition to means, changes in volatility are tracked in reaction to substantial new information, estimated with GARCH‐M methods. The data covers towns in Connecticut and near San Francisco. There is evidence of negative feedback at short lags, contrary to previous research on housing and other assets. There is also evidence of a moving average error process which tends to reverse recent shocks. Significantly positive spatial information diffusion is found from neighboring towns in Connecticut but none in control tests on nonneighboring towns. The results also include evidence of a risk‐reward tradeoff in housing price changes in the San Francisco area.
Determinants of Buyer Search in a Housing Market
Authors: Anglin Paul M.
Published: September 2003

Using data collected from specially‐designed questionnaires, the duration of search by a house buyer is estimated. Duration is measured in two ways: in terms of time and in terms of the number of houses seen. To explain this data, several features must be added to a simple model when search models are applied to a housing market. Many of the statistically significant variables, such as prior information and the quality of information provided by a newspaper or a real estate agent, deal with the provision of information. The type of agency that employs the agent and the characteristics of the buyer have little effect.
The Effects of the Real Estate Crisis on Institutional Stock Prices
Authors: Ghosh Chinmoy , Guttery Randall S. , Sirmans C.F.
Published: September 2003

This article investigates the contagious movement of financial institutions' common stock prices in response to real estate news. The basic hypothesis is that because real estate assets are traded infrequently, the market has incomplete information about their true value. The stock price reaction by banks, thrifts and insurance companies to announcements of poorly performing real estate portfolios is studied. Consistent with the hypothesis, significantly negative reactions obtain, both within and across industries, to these announcements. Reflecting the differential regulatory environment and disclosure policies, insurance companies, in general, react more strongly to adverse real estate news. Also, the price reaction of an individual firm is significantly associated with the level of its real estate exposure.
Changes in REIT Liquidity 1990–1994: Evidence from Intra‐day Transactions
Authors: Bhasin Vijay , Cole Rebel A. , Kiely Joseph K.
Published: September 2003

This study uses data on intra‐day transactions to analyze whether real estate investment (REIT) liquidity as measured by the bid‐ask spread changed from 1990 to 1994, a period during which the industry's market capitalization increased from $8.7 billion to $45 billion. REIT percentage spreads (spread as percentage of share price) narrowed significantly, primarily attributable to higher share prices rather than narrower dollar‐value spreads. An empirical model is used to analyze the determinants of percentage spreads. Return variance and share price, not market capitalization are found to be the primary determinants of percentage spreads in both periods. This suggests that the liquidity of REIT securities is similar to that of non‐REIT securities with similar prices and return variance. In addition, percentage spreads are wider for REITs trading on the NASDAQ.
Mortgage Default in Local Markets
Authors: Capozza Dennis R. , Kazarian Dick , Thomson Thomas A.
Published: September 2003

Using recent theoretical advances and an extensive panel data set on metropolitan areas, this study provides new tests of the contingent claims based model of default. The empirical modeling incorporates a full complement of variables that permit direct tests of the options‐based model including the conditional effects of age and rent‐to‐price ratios. The role of transaction costs and trigger events is examined, and the results confirm the importance of both. The effects of aggregation and short sample periods are explored and demonstrated to affect inference in studies of mortgage default.
Determinants of Performance for Mortgage‐Backed Securities Funds
Authors: Gallo John G. , Buttimer Richard J. , Lockwood Larry J. , Rutherford Ronald C.
Published: September 2003

This article examines the performance of mortgage‐backed securities (MBS) mutual funds from January 1987 to June 1995. As a group, the MBS mutual funds underperform both the Salomon and Lehman Brothers MBS market benchmarks. The relative underperformance of the MBS mutual funds is due to poor securities selection and timing decisions. Fund expenses also contribute significantly to the underperformance, while fund load, turnover, management fees and other fund characteristics do not materially affect performance. The underperformance is found to be concentrated in several exceptionally bad months during the sample period. Testing indicates that the MBS mutual funds underperform the MBS benchmark during months of rising interest rates, but match the MBS benchmark during months of falling interest rates.
Using a Bootstrap to Measure Optimum Mixed‐Asset Portfolio Composition:
Authors: Ziobrowski Alan J. , Cheng Ping , Ziobrowski Brigitte J.
Published: September 2003

Liang, Myer and Webb (1996) have offered bootstrap simulation as a tool for quantifying the uncertainty in the optimum composition of portfolios. Unfortunately, the confidence intervals produced were so large, they were unable to provide any new insight to the question, “How Much in Real Estate?”. In this comment, adjustments have been made to the methodology they proposed and as a result have produced findings which lead to very different conclusions. More specifically, the results suggest that investors with a low risk preference should hold very little real estate.
Weathering the HRT Storm
Authors: Powledge Tabitha M.
Published: September 2003

A torrent of recent clinical studies has reported that hormone replacement therapy (HRT) fails to postpone many diseases of aging and apparently hastens some of them. Interpretations of the work have stranded research on sex hormones and menopause and left millions of women and their physicians at sea about the wisdom of hormone replacement. A new report presents a list of tasks that can help answer the multitude of remaining questions about HRT. But because of HRT's bad reputation, researchers might have a tough time tackling some of the projects that the report urges.
Trouble Starts Within
Authors: Davenport R. John
Published: September 2003

Hurricanes can churn frenzied seas that wash away houses, but ordinary waves can nip at a home's integrity too. Whether the same concept applies to the rain of toxic chemicals in cells is unclear. In lab experiments, deluges of oxygen radicals cripple cells and organisms, but no one knows whether the trickle of compounds produced inside cells during everyday life fosters disease. A new study supports that link, however. Cells with weakened oxidant defenses show dramatic alterations in chromosome structure--changes that can spur cancer and perhaps aging.
Mitotic and Postmitotic Senescence in Plants
Authors: Gan Susheng
Published: September 2003

Plants exhibit both mitotic and postmitotic senescence. Mitotic senescence, also known as proliferative senescence, occurs when germline-like meristem cells lose their ability to undergo mitotic cell division. Unlike replicative senescence in yeast and human cells in culture, mitotic senescence in plants is not controlled by telomere shortening. Postmitotic senescence, an active degenerative process, occurs in organs such as leaves and floral petals. Substantial progress has been made toward understanding the molecular mechanisms of postmitotic senescence (especially leaf senescence). Leaf senescence is a form of programmed cell death that can be regulated by an array of endogenous factors and environmental cues. Gene expression is required in order for leaf cells to die. In
Arabidopsis thaliana
, up to 2500 genes (including more than 130 that encode transcription factors) are transcribed during leaf senescence. Mutant analysis and functional genomics approaches have revealed important roles for several of these genes in leaf senescence. In addition to summarizing our current understanding of senescence in plants at the molecular level, this Review compares mechanisms of senescence in yeast and animal systems.
Dupontia (Poaceae) in North America
Authors: Brysting A K , Aiken S G , Lefkovitch L P , Boles R L
Published: September 2003

Challenged by work on the Panarctic Flora project and apparent discrepancies in recent taxonomic treatments, the genus Dupontia was studied from herbarium specimens, including types and chromosome vouchers, and by numerical taxonomy, mapping the distribution of morphological characteristics, consideration of chromosome numbers, and field work in the Canadian Arctic. Our results using these techniques show random variability in many characters and differences in plant size that appear to be partly habitat related. The treatment of the genus has varied from the recognition of one variable species to three or more distinct species. Morphological characters, used in the literature to divide the genus Dupontia into more than one taxon, cannot be reliably applied to distinguish most North American plants. Continuous morphological variation in combination with high and variable ploidy levels, effective vegetative growth, and rare sexual reproduction suggests the use of a broad species concept. Until further evidence is available, our results support treating the genus as monotypic.Key words: Poaceae, Dupontia, morphology, chromosome numbers, conditional clustering, contingency tables.
Genetic diversity of arctic bramble (Rubus arcticusL. subsp.arcticus) as measured by amplified fragment length polymorphism
Authors: Lindqvist-Kreuze Hannele , Koponen Hilkka , Valkonen Jari P.T
Published: September 2003

The levels of genotypic and genetic variation were estimated in six natural populations of arctic bramble (Rubus arcticus L. subsp. arcticus) in Finland. Using three primer combinations, a total of 117 amplified fragment length polymorphisms (AFLP) were found. The results were highly reproducible and allowed identification of 78 genets among the 122 plants of arctic bramble studied. Genotypic variation measured as Simpson index (D) was high in all populations, ranging from 0.72 to 0.94. Also, the level of genetic variation measured as Shannon index was relatively high in all populations, ranging from 0.19 to 0.32 (average 0.26). The high levels of genetic diversity indicate that sexual reproduction has played a significant role in these populations. The hierarchical analysis of molecular variance (AMOVA) partitioned 48% of the genetic variation among populations, suggesting a high level of population differentiation and a low level of interpopulation gene flow. Genetic diversity among ten currently grown cultivars of arctic bramble and hybrid arctic bramble (R. arcticus subsp. arcticus × R. arcticus subsp. stellatus) was large, and the subspecies were clearly distinguished from each other based on the AFLP marker data.Key words: AFLP, AMOVA, population, natural habitat, Rubus arcticus subsp. arcticus, Rubus arcticus subsp. stellatus.
A comparative morphological study of South African avocado and mango isolates ofColletotrichum gloeosporioides
Authors: Sanders Gina M , Korsten L
Published: September 2003

South African isolates of Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz. from avocado and mango are phenotypically as variable as isolates from other countries over the world. Colony colours ranging from pale salmon pink to dark grey green occurred. Isolates from mango were generally less variable than those from avocados. Most isolates produced appressoria terminally on germ tubes and few differences were observed between appressoria of different isolates, their mean length being 14.6 µm. Four different types of conidial shapes were found, and both avocado and mango isolates produced mainly cylindrical conidia with a tapered base and obtuse apex. Conidial length varied considerably, but width remained relatively constant. No correlation was evident between the length/width ratio of conidia and the virulence of isolates when inoculated into avocado and mango.Key words: Colletotrichum gloeosporioides, conidia, morphology, avocado, mango.
Genetic relationships within the Cucurbitaceae as assessed by consensus chloroplast simple sequence repeats (ccSSR) marker and sequence analyses
Authors: Chung Sang-Min , Decker-Walters Deena S , Staub Jack E
Published: September 2003

To investigate genetic relationships in Benincaseae (19 accessions), Cucurbiteae (1), Joliffieae (2), Melothrieae (2), and Sicyeae (3) tribes of the family Cucurbitaceae, consensus chloroplast simple sequence repeats (ccSSR) primer pairs obtained from tobacco (Nicotiana tabacum L.) chloroplast DNA were used. Variation in the length and putative sequence substitution events of polymerase chain reaction (PCR) products were analyzed. Sequencing of four fragments (ccSSR-1, -7, -8, and -19) revealed that convergence in fragment length occurs in more distant species comparisons. In ccSSR-1 and -8, the same fragment lengths occurred as the result of different insertion and deletion events. Nevertheless, the examination of a large number of ccSSR fragments suggested that this apparent homoplasy could be overshadowed by evolutionary relationships among taxa. This hypothesis is supported by the relative degree of positive congruence of taxon groupings after cluster and principal components analyses performed on both base pair length and sequence substitution data. Moreover, these analyses support previous biochemical and morphological data indicating that distinct lineages exist within the Benincaseae. Likewise, data support the hypotheses that the genus Benincasa is descended from an ancient African ancestor and that the progenitor of the New World Sicyeae tribe shares a common ancestor with the genus Luffa of the Old World Benincaseae.Key words: Benincaseae, chloroplast, consensus, homoplasy, microsatellite, simple sequence repeats.
Development of a peatland complex in boreal western Canada: lateral site expansion and local variability in vegetation succession and long-term peat accumulation
Authors: Bauer Ilka E , Gignac L Dennis , Vitt Dale H
Published: September 2003

The spatial development and vegetation history of a large boreal peatland complex in east-central Alberta was reconstructed to examine factors that control peatland development in continental regions. Peat depth throughout the site was interpolated from over 300 depth measurements, and basal radiocarbon dates were obtained from 16 cores. Peat first initiated about 7400 calibrated 14C years BP (cal. BP), and early peat-forming communities were wet fens or marshes. Rates of expansion from these nucleation sites were dependent on both moisture availability and topography, with asynchronous expansion in different regions. Basal macrofossil assemblages suggest that paludification on slopes of large basins was the result of flooding caused by rising peatland water tables. In many areas that initiated after 3000 cal. BP, paludification involved invasion of upland forest by Sphagnum. Long-term apparent rates of peat accumulation were fastest in wet, moderate-rich fen areas where little community change has occurred over time. Macrofossil analysis of core profiles reveals a tendency for sites that initiated wet and minerotrophic to eventually be colonized by Sphagnum. However, the thickness of surficial Sphagnum layers differs between cores, and there are several examples of minimal or apparently reverse successional development.Key words: peatlands, boreal, paleoecology, vegetation succession, peat accumulation, paludification.
Amplified fragment length polymorphism inElymus elymoides,Elymus multisetus, and otherElymustaxa
Authors: Larson Steven R , Jones Thomas A , McCracken Carrie L , Jensen Kevin B
Published: September 2003

The geographic and phylogenetic significance of amplified fragment length polymorphism within and among 22 Elymus elymoides (Raf.) Swezey subsp. elymoides, 24 E. elymoides subsp. brevifolius (J.G. Sm.) Barkworth, and 13 Elymus multisetus (J.G. Sm.) Burtt-Davy squirreltail accessions was assessed relative to six other North American and three Eurasian Elymus taxa. Elymus elymoides and E. multisetus, comprising Elymus sect. Sitanion (Raf.) Á. Löve, were both monophyletic and closely related compared with other congeners. The monophyly of subsp. elymoides was also supported; subsp. brevifolius, however, was paraphyletic and separated into four genetically distinct groups. Estimates of nucleotide divergence among the five E. elymoides groups range from 0.0194 to 0.0288, with approximately 0.0329 differences per site between E. elymoides and E. multisetus. Corresponding estimates of nucleotide divergence range from 0.0243 to 0.0387 among North American taxa and from 0.0337 to 0.0455 between North American and Eurasian taxa. DNA polymorphism among E. elymoides accessions was correlated with geographic provenance and previously reported quantitative traits. Distinct genetic groups of E. elymoides generally correspond to different geographic regions, whereas divergent E. multisetus and E. elymoides accessions are sympatric. Thus, taxonomic ranks of E. multisetus and E. elymoides were supported and geographic groups within E. elymoides were distinguished.Key words: AFLP, Elymus, nucleotide diversity, squirreltail.
Seasonal patterns of reserve and soluble carbohydrates in mature sugar maple (Acer saccharum)
Authors: Wong B L , Baggett K L , Rye A H
Published: September 2003

Sugar maple (Acer saccharum Marsh.) trees exhibit seasonal patterns of production, accumulation, and utilization of nonstructural carbohydrates that are closely correlated with phenological events and (or) physiological processes. The simultaneous seasonal patterns of both reserve and soluble carbohydrates in the leaves, twigs, branches, and trunks of healthy mature sugar maple trees were characterized. The concentrations of starch and soluble sugars ( sucrose, glucose, fructose, xylose, raffinose, and stachyose) were determined. Starch, the major reserve carbohydrate in sugar maple, is low during the active photosynthetic growth season. Starch is accumulated in the xylem ray tissues in late summer and early fall. During the cold season, there is a close relationship between starch hydrolysisaccumulation and temperature. Soluble sugars increase when starch concentrations decrease during the cold months, and these sugars may play a role in cold tolerance. Patterns of change in the stem tissues are similar to those in the root tissues but with slight differences in the timing.Key words: starch, sucrose, glucose, fructose, raffinose, stachyose.
Notes on Ceratocystis brunnea and some other Ophiostoma species based on partial ribosomal DNA sequence analysis
Authors: Hausner Georg , Reid James
Published: September 2003

Ribosomal gene sequence data were obtained from a nonfruiting culture originally identified as Ceratocystis brunnea R.W. Davidson; this species was considered a nomen dubium by Upadhyay (1981) due to a presumptive lack of teleomorph material. The data showed that C. brunnea is a valid species that should be transferred to Ophiostoma, demonstrating that DNA data can compensate for the presumed or actual lack of morphological features lost during either long-term culturing or disintegration of holotype specimens. Use of partial large ribosomal sequence data to assess the relationship of C. brunnea to other Ophiostoma spp. showed that it is not a synonym of Ophiostoma piliferum (Fr.:Fr.) Syd. & P. Syd. as has been suggested; instead, it appears to be distantly related to Ophiostoma piceae (Münch) Syd. & P. Syd. The data obtained for the Ophiostoma piliferum strains included in this study suggest that hardwood-derived isolates may be distinct from those obtained from conifers. In addition, molecular characters support transferring Ceratocystis pseudonigra Olchow. & Reid, Ceratocystiopsis concentrica (Olchow. & Reid) Upadhyay, Ceratocystiopsis pallidobrunnea (Olchow. & Reid) Upadhyay, and Ceratocystiopsis crenulata (Olchow. & Reid) Upadhyay to Ophiostoma.Key words: rDNA, phylogenetics, Ophiostoma piliferum, Ophiostoma, Ceratocystsis.
Rapid and efficient production of the Pyrenophora tritici-repentis teleomorph
Authors: Friesen T L , Ali S , Stack R W , Francl L J , Rasmussen J B
Published: September 2003

Laboratory conditions were identified for efficient production of the teleomorph of Pyrenophora tritici-repentis, causal agent of tan spot of wheat. Ascopcarp density (pseudothecia/cm2) and timing of ascospore maturity and discharge were determined for the fungus incubated on green or senescent maize leaves under various light regimes at 15 °C. The most rapid ascospore maturity (20 days) and discharge (26 days) occurred in a 12-h photoperiod on green leaves. However, incubation in continuous darkness increased ascocarp density. Rapid and efficient ascospore production was obtained by incubating the fungus on senescent leaves in continuous darkness for 12 days followed by a 12-h photoperiod. This resulted in ascospore discharge in 29 days from a high density of pseudothecia. Further, 95% of pseudothecia sampled contained mature ascospores at the time of first discharge. The maximum ascospore discharge height observed was 8.8 cm. Pseudothecial neck development was positively phototropic.Key words: Drechslera, ascomycete, loculascomycete, tan spot, ascospore, pseudothecium
Morphology and anatomy of extrafloral nectaries in Solanum stramonifolium (Solanaceae)
Authors: Falcão Poliana Figueroa , de A. Melo-de-Pinna Gladys Flávia , Leal Inara R , Almeida-Cortez Jarcilene S
Published: September 2003

Solanum stramonifolium Dunal. (Solanaceae) is a pioneer species very common in the Atlantic forest of northeast Brazil. The plants bear extrafloral nectaries (EFNs) that are frequently visited by ants. Ant exclusion experiments show reduced seed set in plants without ants. This paper describes the morphology and anatomy of the nectary of S. stramonifolium. This species bears structural EFNs, vascularized by both phloem and xylem. The nectary is located around the lower, external surface of the calyx, as a ring of five protuberances. Secretory cells are present only below these protuberances and arranged in several strata. The nectar is secreted by stomata situated on projections above the surface of these protuberances. Nectar secretion begins at the floral bud stage and continues through fruit development. We suggest that production of nectar during the entire reproductive period of S. stramonifolium functions as a mechanism of flower and seed protection.Key words: Solanaceae, Solanum stramonifolium, extrafloral nectaries, ants, plant-ant interactions.