@article {29094,
	title = {The role of ABA in the freezing injury avoidance in two Hypericum species differing in frost tolerance and potential to synthesize hypericins},
	journal = {Plant Cell, Tissue and Organ Culture (PCTOC)},
	year = {2015},
	month = {08-03-2015},
	abstract = {<p>Cold stress is a major environmental factor that limits the distribution of plants and determines the spectrum and amount of secondary metabolites with a protective function. The most studied representative of the genus Hypericum, H. perforatum L. (St. John\&rsquo;s wort), is known as a producer of the photodynamic pigment hypericin, the unique bioactive compound structurally belonging to naphtodianthrones. In relation to the cosmopolitan distribution, we hypothesised that low temperature stress could increase the content of naphtodianthrones as a part of the adaptive mechanisms. Two strategies in preventing the freezing injury in the genus Hypericum were defined. Based on a frost-killing temperature (LT50) in untreated (control) plants and more than a 10 \&deg;C decrease in LT50 in cold-acclimated plants, we demonstrated the freezing tolerance for H. perforatum. On the contrary, the freezing avoidance was preferable in H. canariense\&mdash;the species endemic to (sub)tropical Canary Islands and Madeira. The freezing tolerance/avoidance was related to the course of ABA accumulation/depletion in H. perforatum/H. canariense under a subfreezing temperature of \&minus;4 \&deg;C; however, the effect of dehydration or application of 76 \&mu;M ABA on the level of endogenous ABA was comparable. The 48-h exposure of H. perforatum control plants to \&minus;4 \&deg;C resulted in a 1.6-fold increase in the content of naphtodianthrones, along with the 1.5-fold increase of ABA. On the contrary, neither dehydration nor exogenous ABA stimulated the biosynthesis of these compounds. Our findings indicate possible integration of ABA signalling into naphtodianthrones biosynthesis under subfreezing conditions; this mechanism could be modified by plant tolerance to cold environments.</p>
},
	issn = {0167-6857},
	doi = {10.1007/s11240-015-0748-9},
	url = {http://link.springer.com/10.1007/s11240-015-0748-9},
	author = {Bru{\v n}{\'a}kov{\'a}, Katar{\'\i}na and Petijov{\'a}, Linda and Z{\'a}me{\v c}n{\'\i}k, Ji{\v r}{\'\i} and Ture{\v c}kov{\'a}, Veronika and Cellarova, Eva}
}
@article {29093,
	title = {Spatial chemo-profiling of hypericin and related phytochemicals in Hypericum species using MALDI-HRMS imaging},
	journal = {Analytical and Bioanalytical Chemistry},
	year = {2015},
	month = {08-03-2015},
	abstract = {<p>Advanced analytical imaging techniques, including matrix-assisted laser desorption/ionization high-resolution mass spectrometry (MALDI-HRMS) imaging, can be used to visualize the distribution, localization, and dynamics of target compounds and their precursors with limited sample preparation. Herein we report an application of MALDI-HRMS imaging to map, in high spatial resolution, the accumulation of the medicinally important naphthodianthrone hypericin, its structural analogues and proposed precursors, and other crucial phytochemical constituents in the leaves of two hypericin-containing species, Hypericum perforatum and Hypericum olympicum. We also investigated Hypericum patulum, which does not contain hypericin or its protoforms. We focused on both the secretory (dark glands, translucent glands, secretory canals, laminar glands, and ventral glands) and the surrounding non-secretory tissues to clarify the site of biosynthesis and localization of hypericin, its possible precursors, and patterns of localization of other related compounds concomitant to the presence or absence of hypericin. Hypericin, pseudohypericin, and protohypericin accumulate in the dark glands. However, the precursor emodin not only accumulates in the dark glands but is also present outside the glands in both hypericin-containing species. In hypericin-lacking H. patulum, however, emodin typically accumulates only in the glands, thereby providing evidence that hypericin is possibly biosynthesized outside the dark glands and thereafter stored in them. The distribution and localization of related compounds were also evaluated and are discussed concomitant to the occurrence of hypericin. Our study provides the basis for further detailed investigation of hypericin biosynthesis by gene discovery and expression studies.</p>
},
	issn = {1618-2642},
	doi = {10.1007/s00216-015-8682-6},
	url = {http://link.springer.com/10.1007/s00216-015-8682-6},
	author = {Kusari, Souvik and Sezgin, Selahaddin and Nigutova, Katarina and Cellarova, Eva and Spiteller, Michael}
}
