COMPARATIVE ACTIVITIES OF PHENYLALANINE AMMONIA-LYASE AND TYROSINE AMMONIA-LYASE AND PHENOLIC COMPOUNDS ACCUMULATED IN CASSAVA ELICITED CELL

Plants respond to attack by pathogens by initiating a change in cellular metabolism, leading to synthesis of antifungal proteins, production of phytoalexins and/or accumulation of phenolic compounds, namely lignins and salicylic. Lignins reinforce pectocellulosic cell walls and limit the invasion of plant tissues by pathogens; while salicylic acid plays a role in signals plant defense against pathogens. The objective of this study was to evaluate the activities of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) and tyrosine ammonia-lyase (TAL, EC 4.3.1.5); and to determine the level of their involvement in the biosynthetic pathway of these phenylpropanoids in cells of cassava ( Manihot esculenta Crantz, cv Yac\ue9) elicited with salicylic acid (SA). PAL and TAL activities were demonstrated in crude extract enzyme. PAL activity was 9.8 times greater than that of TAL in the pellet obtained with 20% (w/v) ammonium sulphate. In the extract treated with Dowex 2 (cationic), TAL activity was 36.7 times greater than that of PAL. pH and temperature optima of PAL (8; 40\ub0 C) differed from those of TAL (8.5; 30\ub0 C). In the presence of SA, PAL and TAL activities were respectively maximum 24 and 72 hr after inoculation. TAL activity and induced phenols were much higher than PAL. PAL and TAL activities were optimised respectively, by 75 and 100 \u3bcM of SA. The synthesis of phenolic compounds was concomitant with enzymes stimulation. These results show that PAL is different from TAL and the two enzymes are involved in the biosynthetic pathway of phenylpropanoids in cassava.Les plantes r\ue9pondent \ue0 l\u2019attaque des pathog\ue8nes par l\u2019initiation d\u2019un changement du m\ue9tabolisme cellulaire, conduisant \ue0 la synth\ue8se des prot\ue9ines antifongiques, la production des phytoalexines et/ou l\u2019accumulation des compos\ue9s ph\ue9noliques appel\ue9s lignines et salicyliques. Les lignines renforcent les membranes cellulaires p\ue9ctocellulosiques et limitent l\u2019invasion des tissues des plantes par les pathog\ue8nes, alors que l\u2019acide salicylique joue un r\uf4le dans les signaux de d\ue9fense des plantes contre les pathog\ue8nes. Cette \ue9tude avait pour objectif d\u2019\ue9valuer les activit\ue9s du phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) et du tyrosine ammonia-lyase (TAL, EC 4.3.1.5) ainsi que de d\ue9terminer le niveau de leur implication dans la voie biosynth\ue9tique de ces ph\ue9nylpropanoides dans les cellules de manioc ( Manihot esculenta Crantz, cv Yac\ue9) dues \ue0 l\u2019acide salicylic. Les activit\ue9s PAL et TAL \ue9taient d\ue9montr\ue9es dans un extract de base d\u2019enzyme. L\u2019activit\ue9 PAL \ue9tait 9.8 fois plus \ue9lev\ue9e que celle de TAL dans la boulette obtenue du sulfate d\u2019ammonium (w/v) 20%. Dans l\u2019extract trait\ue9 avec Dowex 2 (cationique), l\u2019activit\ue9 TAL \ue9tait 36.7 fois plus \ue9lev\ue9e que celle du PAL. Le pH et la temp\ue9rature optima de PAL (8; 40\ub0 C) diff\ue9raient de ceux du TAL (8.5; 30\ub0 C). En pr\ue9sence de l\u2019acide salicylique, les activit\ue9s PAL et TAL \ue9taient respectivement maximum \ue0 24 et 72 heures apr\ue8s inoculation. L\u2019activit\ue9 TAL ainsi que les ph\ue9nols induits \ue9taient plus \ue9lev\ue9s que PAL. Les activit\ue9s PAL et TAL \ue9taient plus optimis\ue9es respectivement par 75 et 100 \u3bcM de l\u2019acide salicylique. La synth\ue8se des compos\ue9s ph\ue9noliques \ue9tait concomitante avec la stimulation enzymatiques. Ces r\ue9sultats montrent que PAL est diff\ue9rent de TAL et les deux enzymes sont impliqu\ue9s dans la voie biosynth\ue9tique des ph\ue9nylpropano\ubfdes dans le manioc

SUCCESS AND FAILURE OF AGRICULTURAL FUTURES CONTRACTS

Most new futures contracts fail. This study estimates the effects of several factors on the success or failure of agricultural futures contracts. Commodities with futures markets and without futures markets are included. Characteristics for which no data exist, such as homogeneity, vertical integration, buyer concentration, and activeness of the cash market, are measured by the Delphi approach. An active cash market is found to be necessary for futures contract success since this variable alone perfectly predicts whether or not a commodity has a futures market

Performances Agronomiques De Quelques Varietes De Manioc (Manihot esculenta Crantz) Dans Trois Zones Agroclimatiques De La Cote D\'ivoire

En Côte d\'Ivoire, le manioc est produit sur environ 4/5 du territoire national et occupe le deuxième rang des productions vivrières après l\'igname, avec un volume annuel de 1 700 000 tonnes. Toutefois, la production est confrontée à quelques contraintes majeures dont la culture extensive dévoreuse d\'espace, l\'insuffisance du matériel végétal de plantation, et la persistance des maladies et ravageurs. Pour réduire ces difficultés, la recherche agronomique propose de nouvelles technologies, notamment l\'utilisation de variétés améliorées, créées en station de recherche puis évaluées de façon multilocale. Dans ce contexte, 3 essais variétaux, comportant 6 cultivars locaux et 15 variétés améliorées, ont été conduits de 1997 à 2000 dans 3 zones agroclimatiques de la Côte d\'Ivoire. Les rendements moyens obtenus ont varié entre 8 et 41 t/ha ; 75 % des variétés améliorées ayant obtenu des rendements supérieurs à 20 t/ha. L\'incidence de la mosaïque africaine (plus de 90 %) sur les cultivars traditionnels a été statistiquement supérieure à celle observée sur les variétés améliorées. En revanche, l\'incidence des acariens sur le même matériel végétal a été mitigée. Ainsi, les variétés les plus performantes sont proposées au développement ou à des évaluations complémentaires en culture paysanne.In Côte d\'Ivoire, cassava is grown on about 4/5 of the national territory and is the major food crop after yam, with an annual production of 1 700 000 tons. However, cassava production is limited by major constraints such as low intensification, insufficiency of planting material and endemic pests and diseases. To face these constraints, new technologies were developed for farmers through agricultural research such as improved varieties. These varieties were tested on other experimental stations as well as multilocal observation sites. In line with that strategy, 6 local cultivars and 15 improved varieties were assessed in three agroclimatic zones of Côte d\'Ivoire from 1997 to 2000. Average cassava yields observed ranged from 8 to 41 t/ha ; 75 % of improved varieties having performed more the 20 t/ha. Also, cassava cultivars were highly affected by the african mosaic virus as compared to improved varieties. However, neither cultivars nor improved varieties were differently affected by mytes attacks. Therefore, improved varieties were recommended for extension service as well as for additional tests in small scale farming conditions. Keywords: manioc, cultivar, mosaïque africaine, acarien, Côte d'Ivoire; cassava, cultivar, african mosaic, myte, Côte d'IvoireAgronomie Africaine Vol. 16 (2) 2004: pp. 1-

SUCCESS AND FAILURE OF AGRICULTURAL FUTURES CONTRACTS

Most new futures contracts fail. This study estimates the effects of several factors on the success or failure of agricultural futures contracts. Commodities with futures markets and without futures markets are included. Characteristics for which no data exist, such as homogeneity, vertical integration, buyer concentration, and activeness of the cash market, are measured by the Delphi approach. An active cash market is found to be necessary for futures contract success since this variable alone perfectly predicts whether or not a commodity has a futures market.active cash market, buyer concentration, Delphi approach, futures markets, homogeneity, open interest, volume, Marketing,

GARCH option pricing with implied volatility

Generalized autoregressive conditional heteroskedasticity (GARCH) option pricing models (OPM) with historical volatility have proven superior to the log-normality assumption of the Black option pricing model with historical volatility. This paper estimates implied volatilities from GARCH OPM. The estimated implied volatilities are used to forecast option premia. The GARCH OPM with implied volatility provided more accurate estimates of option premia than the Black option pricing model with implied volatility for options ranging from six to sixteen days to maturity. For options ranging from 21 to 50 days to maturity the Black OPM with implied volatility was more accurate than the GARCH OPM with implied volatility.

Garch Option Pricing with Implied Volatility

Generalized autoregressive conditional heteroskedasticity (GARCH) provides a better ft to futures price data than the common assumption of identical independent normal distribution. GARCH option pricing models (OPM) with historical volatility have proven superior to the log-normality assumption of the Black option pricing model with historical volatility. Implied volatilities derived from GARCH OPM might therefore be expected to provide better guidance in investment decisions than those derived from the Black option pricing model. This paper estimates implied volatilities from GARCH OPM. The estimated implied volatilities are used to forecast option premia. Results are compared against forecasts of option premia using implied volatilities from Black's option pricing model. The GARCH implied volatilities are more stable than the Black implied volatilities. The GARCH option pricing model with implied volatility outperformed the Black option pricing model with implied volatility in terms of forecasting actual option premia