Ultraviolet-B radiation induces the accumulation of UV-absorbing pigments of the flavonoid type in the epidermal layer of rye seedlings. The content of pigments identified as isovitexin derivatives was about 4 times higher in leaves preirradiated for up to 24 h with long wavelength UV-B radiation as compared to control plants without any UV-B pretreatment. Leaves preconditioned in this way could prevent or reduce damage to photosynthetic function caused by short wavelength UV-B radiation. Photosynthetic activity monitored by variable fluorescence was reduced in unprotected leaves compared to protected leaves when expressed as a fluorescence decrease ratio value, as quantum yield of photosystem I1 (Fvm/Fm) or as leaf vitality index (FmiFo).

Trans‐cinnamic acid is the product of the L‐phenylalanine ammonia lyase (PAL, EC 4.3.1.5) enzyme reaction and might regulate the subsequent phenylpropanoid synthesis by feedback inhibition of PAL activity. The partial conversion of trans‐cinnamic acids (e.g. trans‐p‐coumaric acid) and of trans‐p‐coumaryl‐glucoside (chemically synthesized model substance for cinnamic acid derivatives) to the cis isomers upon UV irradiation leads to reduced inhibition of PAL activity within minutes. In rye leaves this rapid enhancement of PAL activity (within minutes) causes a rapid increase in phenylpropanoids, which are predominantly located in the epidermal layer. Because phenylpropanoid derivatives are precursors of flavonoid biosynthesis, the observed rapid increase in flavonoid content after short‐term UV irradiation can be explained by this UV‐induced regulation mechanism. Consequently, transphenylpropanoids can be regarded as photoreceptors and regulators of the phenylpropanoid pathway during UV‐B (280–320nm) irradiation. In rye leaves an additional slower UV response, obviously by induction of genetic transcription as described for other plant systems, leads to a much greater flavonoid accumulation compared to the rapid induction.

The conversion of penicillin G into 6-aminopenicillanic acid (6-APA) is a very important reaction, 6-APA being the basic raw material for the industrial production of semisynthetic penicillins. Bulk 6-APA can be achieved either by chemical' or enzymatic hydrolysis. Each system has its advantage. However, because of improvements in immobilization techniques that promote stability and prolonged high activity, enzymatic hydrolysis has become a major alternative to chemical hydrolysis. The industrial route for 6-APA bioproduction was developed ca. 1960 and it can be assumed that almost all 6-APA is produced today by the immobilized enzymatic route.Numerous immobilization techniques for penicillin acylase have been tried on a laboratory scale. For instance, adsorption, crosslinking, covalent and physical attachment, and entrapment methods have been described.' However, more efficient procedures to obtain 6-APA are still being investigated and the immobilization of penicillin G acylase on a polysaccharide matrix, such as chito~an,~ by an economical and simple procedure could undergo an interesting biocatalyst .We have prepared different physical forms of chitosan (powder, particules, and beads), glyoxal reticulated or not, and used them as carriers to immobilize penicillin G acylase either by adsorption followed by reticulation with glutaraldehyde or by direct crosslinking to the matrix pretreated with glutaraldehyde. The first results of our experiments as well as the catalytic evaluation of the resins obtained are described in the present communication. MATERIALS AND METHODSPenicillin G and penicillin G acylase were a gift from Rhone-Poulenc; penicillin G acylase (0.25 U/mg protein) from E . coli was an acetone precipitate where no detectable p-lactamase activity was found (see below). Crab-shell chitosan was supplied by Rousselot (France); the degree of deacetylation was estimated by titrimetry4 to be more than 64%. Different reagents were synthetic grade products and were * To whom all correspondence should be addressed used without further purification: buffer A -0.005M phosphate buffer, pH 7.5, and buffer B -0.1 M phosphate buffer, pH 8 .00. Spectrophotometric measurements were made with a DU-8 Beckman spectrometer and the pH was regulated either with a Metrohm pH-stat or with a home-made regulation unit connected to a microcomputer (Apple IIe). Preparation of SupportsDifferent physical forms of matrices were prepared from the same chitosan solution (1 g chitosan dissolved in 15 mL of 5% acetic acid in water and filtered to remove insoluble materials). Powder was obtained by pouring dissolved chitosan into excess solution of 0.5M sodium hydroxide; it was collected by centrifugation and thoroughly washed with distilled water until neutrality.Particles were prepared at 25°C by addition of 0.1M sodium hydroxide to a stabilized (0.1-0.5% Tween SO) emulsion obtained by mixing the acetic acid solution of chitosan with cyclohexane (1 : 1). The particles were then washed in distilled water until neutrality and sized (0....

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