Review
Biosynthesis of flavonoids and effects of stress

https://doi.org/10.1016/S1369-5266(02)00256-XGet rights and content

Abstract

The accumulation of red or purple flavonoids is a hallmark of plant stress. Mounting evidence points to diverse physiological functions for these compounds in the stress response. Advances are also being made toward understanding how plants control the types and amounts of flavonoids that are produced in response to different cues.

Introduction

Flavonoids are ubiquitous plant secondary products that are best known as the characteristic red, blue, and purple anthocyanin pigments of plant tissues [1]. These compounds serve essential functions in plant reproduction by recruiting pollinators and seed dispersers. They are also responsible for the beautiful display of fall color in many plant species, which has recently been suggested to protect leaf cells from photo-oxidative damage, thereby enhancing the efficiency of nutrient retrieval during senescence [2•]. In fact, flavonoids are a remarkably diverse group of secondary products (Fig. 1) with a vast array of biological functions, including apparent roles in stress protection. The flavonols may be among the most important flavonoids in this regard; they are the most ancient and widespread of the flavonoids, synthesized even in mosses and ferns, and have a wide range of potent physiological activities [3]. Progress continues to be made in understanding the roles of flavonoids in stress protection, as well as in defining the mechanisms that control the amounts and varieties of flavonoids that are produced in plants in response to diverse environmental cues [4].

Section snippets

Flavonoids and stress protection

The ultra-violet (UV)-absorbing characteristics of flavonoids have long been considered to be evidence for the role of flavonoids in UV protection. Indeed, flavanoids are often present in the epidermal cell layers of leaves and in tissues that are susceptible to UV light, such as pollen and the apical meristem. The first direct evidence in support of a role for flavanoids in UV protection came from experiments with Arabidopsis mutants, which showed that lesions in chalcone synthase (CHS) or

Transcriptional regulation of the flavonoid pathway

One important avenue to understanding the role of flavonoids in the stress response is to understand how the expression of the biosynthetic pathway is regulated. This system represents one of the oldest examples of coordinated gene and enzyme regulation in response to environmental and developmental factors [24]. A great deal has been learned from studies in a variety of plant species, primarily about transcriptional regulation, although evidence for other types of control also exists. Recent

Enzymology of flavonoid biosynthesis

Many, although not all, of the enzymes of flavonoid biosynthesis are encoded by small gene families. The functional significance of this redundancy has been the subject of substantial interest over the years. Kimura et al. [32•] reported recently that licorice (Glycyrrhiza echinata) contains two CHI isozymes that can use both 6′-hydroxychalcone and 6′-deoxychalcone, and therefore are likely to be involved in the legume-specific isoflavonoid pathway (Fig. 1). One of these genes is induced by

Conclusions

The accumulation of anthocyanin pigments in vegetative tissues is a hallmark of plant stress, yet the role that flavonoids play in the stress response is still poorly understood. In many cases, these compounds may provide antioxidant activity as part of a general stress response, which may also explain their health-promoting qualities in animals. However, there is also evidence that flavonoids may function in plants to screen harmful radiation, bind phytotoxins, and help to regulate the stress

References and recommended reading

Papers of particular interest, published within the annual period of review, have been highlighted as:

  • • of special interest

  • •• of outstanding interest

References (41)

  • I.S Booij-James et al.

    Ultraviolet-B radiation impacts light-mediated turnover of the photosystem II reaction center heterodimer in Arabidopsis mutants altered in phenolic metabolism

    Plant Physiol

    (2000)
  • K.G Ryan et al.

    Flavonoid and UV photoprotection in Arabidopsis mutants

    Z Naturforsch

    (2001)
  • K Bieza et al.

    An Arabidopsis mutant tolerant to lethal ultraviolet-B levels shows constitutively elevated accumulation of flavonoids and other phenolics

    Plant Physiol

    (2001)
  • P.S Kidd et al.

    The role of root exudates in aluminium resistance and silicon-induced amelioration of aluminium toxicity in three variety of maize (Zea mays L.)

    J Exp Bot

    (2001)
  • P Dietrich et al.

    The role of ion channels in light-dependent stomatal opening

    J Exp Bot

    (2001)
  • M Jacobs et al.

    Naturally occurring auxin transport regulators

    Science

    (1988)
  • I.J Faulkner et al.

    Flavonoids and flavonoid sulphates as probes of auxin-transport regulation in Curcurbita pepo hypocotyl segments and vesicles

    Planta

    (1992)
  • P Bernasconi

    Effect of synthetic and natural protein tyrosine kinase inhibitors on auxin efflux in zucchini (Curcurbita pepo) hypocotyls

    Physiol Plant

    (1996)
  • D.E Brown et al.

    Flavonoids act as negative regulators of auxin transport in vivo in Arabidopsis thaliana

    Plant Physiol

    (2001)
  • A Murphy et al.

    Regulation of auxin transport by aminopeptidases and endogenous flavonoids

    Planta

    (2000)
  • Cited by (1527)

    View all citing articles on Scopus
    View full text