A new source to produce a significant quantity of a naturally occurring polyphenol, piceatannol, was investigated in this study. Both resveratrol and piceatannol are recognized as important ingredients in functional foods due to their beneficial health effects. However, unlike resveratrol, the piceatannol concentration in plants is very low. Thus, calluses of peanuts, an easily obtainable source, were chosen as the material to induce piceatannol production under controlled conditions. To induce resveratrol and piceatannol, calluses were exposed to the ultraviolet (UV) irradiation. Significant quantities of resveratrol and piceatannol were produced by calluses upon UV irradiation in both static and suspension culture conditions. The amounts of piceatannol and resveratrol produced in 1 g of calluses ranged from 2.17 to 5.31 microg and from 0.25 to 11.97 microg, respectively, in static culture. In suspension culture, the amounts of induced piceatannol and resveratrol were somewhat lower. The quantities of induced piceatannol and resveratrol reached a maximum at 18 h after UV irradiation treatment in static culture. In contrast, the levels of resveratrol and piceatannol remained almost constant throughout the experiments in suspension culture. The piceatannol produced by calluses in all studies was much higher than the values reported in the literature, whereas the resveratrol produced was comparable to reported values.

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It is well-known that the invasion of microbes such as fungi in some plants, including peanut, can induce the biosynthesis of stilbenoids such as trans-resveratrol and trans-piceatannol. However, in a recent study it was found that not all kinds of microorganisms possessed such potential. The Gram-negative bacterium Pseudochrobactrum asaccharolyticum isolated from the peanut callus failed to act as an elicitor. After systematic investigation, the different inductive effects between fungi and Gram-negative bacteria were attributed to the chitin content of the cell wall. Results showed significantly more trans-resveratrol and trans-piceatannol was induced by fungi (8.92-16.35 and 2.15-7.01 microg/g of fresh calluses, respectively) than by bacteria (1.77-2.72 and 0.16-0.52 microg/g of fresh calluses, respectively), regardless of species and viability. Such great differences prompted the direct utilization of chitin, the distinctive component of fungal cell wall, as an elicitor. The results that trans-resveratrol induced by chitin was about two-thirds the amount induced by sterilized fungi, whereas trans-piceatannol (2.55+/-0.60 microg/g) was close to that by sterilized fungi, revealed chitin is not only an important fungal constituent responsible for the induction of trans-resveratrol and trans-piceatannol but also an efficient elicitor by itself. These findings suggested sterilized fungi and chitin can be used as a safe and fast elicitor, as far as the risk of viable microbes is concerned, to induce trans-resveratrol and trans-piceatannol in the well-controlled peanut tissue culture.