Phenolics during early development of Betula pubescens seedlings: inhibition of phenylalanine ammonia lyase

Abstract

We studied phenolic metabolism and plant growth in birch seedlings at the beginning of their development by inhibiting phenylalanine ammonia lyase (PAL), which is the first committed step in phenylpropanoid metabolism. Betula pubescens (Ehrh.) seeds were germinated in inhibitor-free media and the seedlings were transferred to hydroponic culture at the cotyledon stage. They were 6 days old at the start of the experiment, which lasted for 3 weeks. PAL activity was inhibited by three different concentrations of 2-aminoindane-2-phosphonic acid monohydrate (AIP) in the growing media. At the end of 3 weeks, phenolics in all plant parts (roots, stem, cotyledons, first, second and third true leaves) were determined. AIP inhibited strongly the accumulation of phenolic acids, salidroside, rhododendrins, ellagitannins and their precursors, flavan-3-ols, and soluble condensed tannins. The accumulation of lignin and flavonol glycoside derivatives was moderately inhibited. The accumulation of flavonol glycosides, such as quercetin glycosides and kaempferol glycosides, was not generally inhibited, even in leaves that emerged during the experiment, while the accumulation of insoluble condensed tannins was inhibited only slightly and not in all plant parts. This suggests that flavonol glycosides, which may have a UV-B protective role, and insoluble condensed tannins, which may have structural functions, are prioritized in seedling development. Inhibition of PAL with AIP decreased seedling growth and possible reasons for this are discussed. AbbreviationsAIP 2-Aminoindane-2-phosphonic acid monohydrate PAL Phenylalanine ammonia lyase Phe L-Phenylalanine Trp L-Tryptophan Tyr L-Tyrosine Communicated by P. von Aderkas. Electronic supplementary material The online version of this article (

Significance of phenols in cadmium and nickel uptake

“…The absence of growth changes induced by AIP application in the present study is in contradiction to previous reports from Salix pentandra (stimulation, Ruuhola and Julkunen-Tiitto, 2003) or Betula pubescens (inhibition, Keski-Saari et al, 2007), indicating different sensitivity of plant species and/or ontogenetic stages in comparison with our chamomile plants. On the other hand, the absence of growth inhibition allows us to interpret metabolic responses more objectively.…”

Vole response to unintentional changes in the chemistry of GM poplars

“…The effect of tannins on vole growth and survival depends on the protein content of the forage (Harju 1996). Finally, although phenolics seemingly are affected in a similar way, although not always to the same degree, in leaves as in shoots following metabolic modifications (Keski-Saari et al 2007) we can not with certainty say that the chemical changes in shoots, eaten by the voles, were identical to those in the leaves we analysed.…”

“…However, the general composition patterns of phenolics are usually similar in leaves and stems (for comparison, see Julkunen-Tiitto 1989; Ruuhola & Julkunen-Tiitto 2000). In addition, there are indications that phenolics are affected in a similar way, although not always to the same degree, in leaves as in shoots following metabolic modifications (Keski-Saari et al 2007). Thus, it seem likely to assume that similar, albeit not identical, changes might occur in shoots as in leaves but we can not with certainty say that this was the case.…”

Tannins and Tannin Agents

“…The complex formation is suggested to be one reason for the difficulties of isolation or insolubility of tannins (Porter, 1992). The soluble and insoluble fractions vary among species, sometimes the insoluble fraction may be even higher than the soluble one and is seen as giving a high anthocyanidin (butano/HCl method) or ellagic acid (acid degradation) yield on hydrolysis of the extracted residue (Porter, 1992;Scalbert, 1992;Keski-Saari et al, 2007). However, the extraction conditions, especially temperature, will have a marked effect on tannin extractability.…”

“…HTs are especially abundant in roots of several woody species (e.g. KeskiSaari and Julkunen-Tiitto, 2003;Keski-Saari et al, 2007). A high content of tannins is found in galls induced in plants by herbivores (e.g.…”