Leroy L. Creasy

The increase in phenylalanine ammonia-lyase activity in strawberry leaf disks and its correlation with flavonoid synthesis

Abstract Phenylalanine ammonia-lyase (PAL) activity increased rapidly on exposure of leaf disks to light. The activity increase was necessary to permit the high rates of flavonoid synthesis in leaf disks and was correlated with the rates of synthesis of flavonoids. Although light stimulated the increase in PAL activity, the increase was not altered by short exposure to Red or Far-red light as was flavonoid synthesis.

The significance of carbohydrate metabolism in flavonoid synthesis in strawberry leaf disks

Abstract The production of phenylalanine ammonia-lyase and flavonoids in illuminated strawberry leaf disks was dependent on a supply of carbon dioxide, while in darkness carbon dioxide had no effect on the small rates of production. An external supply of sucrose could remove the carbon dioxide dependency of flavonoid and phenylalanine ammonia-lyase production and a supply of carbon dioxide could remove the stimulation of phenylalanione ammonia-lyase and flavonoid production brought about by external sucrose. The uptake and metabolism of external sucrose by leaf disks was stimulated by light and the light-stimulated uptake was inhibited by DCMU. The synthesis of flavonoids and phenylalanine ammonia-lyase were inhibited by DCMU probably through its inhibition of CO 2 fixation or sucrose uptake. Photosynthesis and carbohydrate metabolism were found to be of extreme importance in controlling the synthesis of flavonoids in leaf disks.

Phenylalanine ammonia lyase-inactivating system in sunflower leaves

Abstract A high MW fraction extracted from sunflower leaves inactivates the phenylalanine ammonia-lyase (PAL) from sunflower and Rhodotorula glutinus . The pH optimum for inactivation was 9·5. The K m of the phenylalanine ammonia-lyase-inactivating system (PAL-IS) was estimated to be 35 mU PAL/ml. D-phenylalanine was an effective inhibitor of inactivation. Fresh tissue had a low level of PAL-IS, but the level increased upon sucrose treatment with light and was maintained during subsequent treatment of leaves in darkness on water.

An anthocyanin-decolorizing system in florets of cichorium intybus

Abstract The anthocyanins of the chicory floret were decolorized by an enzyme system prepared from the florets. The activity of this enzyme and the anthocyanin content of the florets decreased through the day. This enzyme required the presence of catechol, or a similar substance, in the reaction mixture, and decolorized delphinidin glycosides more readily than other anthocyanins.

Anomalous effects of cycloheximide on phenylalanine ammonia-lyase: role of synthesis and inactivation in leaf disks of helianthus annuus*☆

Abstract The activity of phenylalanine ammonia-lyase (PAL) increases dramatically in leaf disks of sunflower (Helianthus annuus) cultured on 0.1 M sucrose in the dark. If disks are subsequently transferred to water, PAL activity decays rapidly. After inactivation the level of PAL can be increased again by transferring the tissue back to sucrose. The initial increase in PAL activity appears to involve an increase in the rate of PAL formation and the appearance is inhibited by cycloheximide. Inactivation of the enzyme is also inhibited by cycloheximide. A comparison of cycloheximide inhibition at different concentrations showed that inactivation was much more sensitive to the inhibitor than PAL formation. The rate of PAL inactivation was very low in fresh disks placed directly on water ( t 1/2 = > 1 day) but increased greatly after culture on sucrose ( t 1/2 = 2 to 4 hr). Therefore, culture appears to increase PAL inactivation as well as PAL formation. Reappearance of PAL activity after inactivation is stimulated rather than inhibited by cycloheximide. The change in effect of cycloheximide from inhibition to apparent stimulation can best be explained by the observation that (1) the turnover of PAL, both formation and inactivation, increases greatly as a result of culture on sucrose and (2) inactivation is more sensitive to cycloheximide than formation. Thus, even where an anomalous cycloheximide insensitive appearance of PAL activity occurs, a mechanism other than reactivation of the enzyme may be involved.

Role of phenylalanine in the biosynthesis of flavonoids and cinnamic acids in strawberry leaf disks

Abstract Alteration of the turnover of phenylalanine ammonia-lyase and cinnamic-4-hydroxylase in leaf disks actively synthesizing phenolics was accomplished by inhibition and by withholding substrate. Measurement of the result of these manipulations on the accumulation of cinnamic acids and flavonoids suggested that the ammonia-lyases are obligatory enzymes in phenolic synthesis but are not necessarily rate limiting.

Biochemical Responses of Plants to Fungal Attack

This review will concentrate on developments in the literature since the publication of excellent reviews edited by Bailey and Mansfield) and by Wood2 which should be consulted for a general overview. It is written with the preformed conclusion that active defense mechanisms are involved in fungi-plant interactions resulting in the resistance of some plants to some fungi.

Sequence of development of autumn coloration in Euonymus

Abstract Low temperature inductive treatment of resting Euonymus plants sequentially resulted in the loss of chlorophyll, an increase in carbohydrate content, an increase in the activity of phenylalanine ammonialyase followed by an accumulation of cinnamic acids and flavonols and finally by the accumulation of flavolans and anthocyanins. These changes were contrasted with changes resulting from low temperature treatments of actively growing plants which are physiologically not capable of the sequence leading to normal autumn coloration.

The effects of sunflower l-phenylalanine ammonia-lyase inactivating factor on Rhodotorula glutinis l-phenylalanine ammonia-lyase

Abstract Phenylalanine ammonia-lyase inactivating factor (IF) prepared from chloroplasts isolated from sunflower leaves was utilized to study its inactivating effects on l -phenylalanine ammonia-lyase from Rhodotorula glutinis in vitro. The effects of inactivation by inactivating factor were compared with those caused by chemicals such as sodium borohydride and nitromethane. The sunflower inactivator acted as an enzyme and enzymatic inactivation caused irreversible loss of phenylalanine ammonia-lyase catalytic activity accompanied by shortening of the enzyme molecule. However, the capacity of IF-inactivated phenylalanine ammonia-lyase to bind to l -phenylalanine, the enzyme substrate, was maintained. These effects of the inactivating factor from sunflower leaves are quite different from those of inhibitors (reversible loss of catalytic activity) isolated from different sources by other workers. The results suggest that inactivation plays an important role in in vivo regulation of phenylpropanoid metabolism.

Grape Anatomy and Physiology

Grapes are vines that are cultivated in temperate climates around the world. There are an estimated 8000 grape varieties grown for consumption. The latest data showed table grape production of about 20 million tons. Vine growth and floral initiation result in the berry formation of the subsequent year. The growth and maturation of the grape berry and/or seeds affect changes in sugars, acids, and phenolic compounds. Pests and diseases are numerous as are the continuous searches for better chemical control. Natural resistance such as the grape plants’ ability to escape infection through anatomical attributes and the production of phytoalexins such as resveratrol also play important roles in control of diseases. Grapes are a multiuse crop with nutritional and pharmaceutical applications.