Target specific post-harvest treatment by gamma radiation for the microbial safety of dried Melissa officinalis and Aloysia citrodora.

This study aimed to assess a specific gamma radiation dose to be applied as a post-harvest process to guarantee the microbial safety of two medicinal plants, Melissa officinalis and Aloysia citrodora. Dried plants treated with gamma radiation indicated that a dose of 5 kGy could be applied as a post-harvest treatment process of M. officinalis and A. citrodora, assuring the microbial safety of dried medicinal plants and lowering the potentiality of deleterious effects on plants' quality attributes. This will enhance the safety and quality of the dried plants to be used as raw materials in industrial applications.

Improvement in drought tolerance of lemon balm, Melissa officinalis L. under the pre-treatment of LED lighting.

Stress priming (pre-exposure of plants to various types of moderate stresses) could affect plant responses to subsequent severe stresses. Drought stress is one of the major threats to plants which reduces the global agricultural productions. Here we demonstrated that light emitting diodes (LEDs)-driven tolerant to drought stress in lemon balm plantlets was highly correlated with priming with these lighting sources. Plantlets of the two genotypes of M. officinalis L. were first grown in 4 incubators with different LED lamps, including white LEDs (380-760 nm), blue LEDs (460 nm), red LEDs (650 nm) and red + blue LEDs (70%:30%), in a greenhouse for 4 weeks. The potted plants were then subjected to drought stress. Under drought stress, LED-primed plants maintained significantly higher fresh and dry weight, relative water content (RWC), concentration of soluble sugars, antioxidant activity and higher content of proline, H2O2, abscisic acid (ABA) and rosmarinic acid than non-primed plants. The results of Real-Time RT-PCR confirmed that LED pretreatment up-regulated the expression levels of respiratory burst oxidase homologues (RBOHs) or NADPH oxidase, 9-cis epoxy carotenoid dioxygenase (NCED), and rosmarinic acid synthase (RAS), while down-regulated that of ABA 8'-hydroxylase (ABA8Ox). These findings suggest, for the first time, that pre-treatment of plants with red + blue LEDs could improve their growth and quality under drought stress.

Effects of PAR and UV-B radiation on herbal yield, bioactive compounds and their antioxidant capacity of some medicinal plants under controlled environmental conditions.

Photosynthetically active radiation (PAR) and Ultraviolet B (UV-B) radiation are among the main environmental factors acting on herbal yield and biosynthesis of bioactive compounds in medicinal plants. The objective of this study was to evaluate the influence of biologically effective UV-B light (280-315 nm) and PAR (400-700 nm) on herbal yield, content and composition, as well as antioxidant capacity of essential oils and polyphenols of lemon catmint (Nepeta cataria L. f. citriodora), lemon balm (Melissa officinalis L.) and sage (Salvia officinalis L.) under controlled greenhouse cultivation. Intensive UV-B radiation (2.5 kJ m(-2)  d(-1) ) influenced positively the herbal yield. The essential oil content and composition of studied herbs were mainly affected by PAR and UV-B radiation. In general, additional low-dose UV-B radiation (1 kJ m(-2) d(-1) ) was most effective for biosynthesis of polyphenols in herbs. Analysis of major polyphenolic compounds provided differences in sensitivity of main polyphenols to PAR and UV-B radiation. Essential oils and polyphenol-rich extracts of radiated herbs showed essential differences in antioxidant capacity by the ABTS system. Information from this study can be useful for herbal biomass and secondary metabolite production with superior quality under controlled environment conditions.

Global profiling of ultraviolet-induced metabolic disruption in Melissa officinalis by using gas chromatography-mass spectrometry.

Melissa officinalis contains various secondary metabolites that have health benefits. Generally, irradiating plants with ultraviolet (UV)-B induces the accumulation of secondary metabolites in plants. To understand the effect of UV-B irradiation on the metabolism of M. officinalis, metabolomics based on gas chromatography-mass spectrometry (GC-MS) was used in this study. The GC-MS analysis revealed 37 identified metabolites from various chemical classes, including alcohols, amino acids, inorganic acids, organic acids, and sugars. The metabolite profiles of the groups of M. officinalis irradiated with UV-B were separated and differentiated according to their irradiation times (i.e., 0, 1, and 2 h), using principal component analysis (PCA) and hierarchical clustering analysis (HCA), respectively. The PCA score plots of PC1 and PC2 showed that the three groups with different irradiation times followed a certain trajectory with increasing UV-B irradiation. HCA revealed that metabolic patterns differed among the three groups, and the 1 h-irradiated group was more similar to the control group (0 h) than the 2 h-irradiated group. In particular, UV-B irradiation of plants led to a decrease in sugars such as fructose, galactose, sucrose, and trehalose and an increase in metabolites in the tricarboxylic acid cycle, the proline-linked pentose phosphate pathway, and the phenylpropanoid pathway. This study demonstrated that metabolite profiling with GC-MS is useful for gaining a holistic understanding of UV-induced changes in plant metabolism.

Are saturating pulses indeed saturating? Evidence for considerable PSII yield underestimation in leaves adapted to high levels of natural light.

The "saturating pulse" method of in vivo Chl fluorescence measurement has been widely used by physiologists and especially ecophysiologists, as it allows a simple, rapid and non-invasive assessment of PSII function and the allocation of absorbed energy into photochemical and non-photochemical processes. It is based on the accurate determination of the so-called Fm('), i.e. the fluorescence signal emitted when a "saturating" light pulse closes all PSII centers. In this methodological investigation, we examined whether the saturating pulse intensities required to obtain maximal fluorescence yields differ between leaves of various species receiving varying actinic light irradiances. It was shown that, in leaves adapted to comparatively high (yet realistic) levels of natural irradiances, the saturating pulses usually applied are not able to close all PSII reaction centers. As a result, there is a high risk of considerable Fm(') underestimation. Accordingly, the derived values of effective PSII yields and linear electron transport rates (ETR) are also underestimated, even at the highest saturation pulse levels afforded by commercial instruments. Since the extent of underestimation increases with actinic irradiance, the ETR versus light curves are considerably distorted. The possible reasons for the apparent inability of "saturating" pulses to close all PSII centers at high actinic light and the practical implications, especially in field work, are discussed.