Abstract
The liverwort Marchantia polymorpha subsp. ruderalis is an emerging model plant, and some data are available on its responses to ultraviolet (UV) radiation. However, it is unknown if the developmental stage of the thalli modulates the effects of UV radiation on the contents of potentially protecting phenolic compounds. To fill this gap, liverwort samples were exposed or non-exposed to UV radiation for 38 days under controlled conditions, using three developmental stages: gemmae (G), one-month thalli (T1), and two-month thalli (T2). Then, the bulk level of methanol-soluble UV-absorbing compounds and the contents of six flavones (apigenin and luteolin derivatives) were measured. The UV responsiveness decreased with thallus age: G and T1 plants were the most UV-responsive and showed a strong increase in all the variables, with G plants more responsive than T1 plants. In UV-exposed T2 plants, only apigenin derivatives increased and more modestly, probably due to a lower acclimation capacity. Nevertheless, the thalli became progressively tougher due to a decreasing water content, representing a possible structural protection against UV. In UV-exposed plants, the temporal patterns of the accumulation of phenolic compounds were compound-specific. Most compounds decreased with thallus age, but di-glucuronide derivatives showed a bell-shaped pattern, with T1 plants showing the highest contents. A Principal Components Analysis (PCA) ordination of the different samples summarized the results found. The patterns described above should be taken into account to select thalli of an adequate developmental stage for experiments investigating the induction of phenolic compounds by UV radiation.
Highlights
The biochemical and physiological processes occurring in plants, and their responses to the environment, are affected by the developmental stage of tissues and organs [1], which is usually related to their age
A total of six individual soluble UV-absorbing compounds (SUVACs) were identified in the liverwort extracts (Figure 1): apigenin 7-O-glucuronide, apigenin 7,40 -di-O-glucuronide, luteolin 30 -O-glucuronide, luteolin 40 -O-glucuronide, luteolin 7-O-glucuronide, and luteolin 7,30 -di-O-glucuronide
Apigenin 7-O-glucuronide was the most abundant compound, under the ruderalis Tak-1 samples exposed to the two radiation regimes imposed in the experiment: P (only only photosynthetically active radiation (PAR), blue line) and PAB (PAR + UV-A + UV-B, red line)
Summary
The biochemical and physiological processes occurring in plants, and their responses to the environment, are affected by the developmental stage of tissues and organs [1], which is usually related to their age. Physiological variations between young and mature (or old) shoots and thalli have been found. Differences in nutrients and heavy metals along the bryophyte profile have been studied in detail [5,6,7,8], as well as the distribution of waxes and other lipids as a function of shoot age [9,10]. The distribution of phenolic compounds in the bryophyte gametophore, as influenced by the developmental stage, has received less attention [4], despite its importance as a protection mechanism against various adverse factors, such as cold, desiccation, herbivory or ultraviolet (UV) radiation. No study has been conducted to our knowledge on the effects of UV radiation on the accumulation of phenolic compounds in different developmental stages of bryophytes
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