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ROOTING IN ARTEMISIA ALBA TURRA AS A MODELLING CLUE IN CHLOROPLAST ARCHITECTURE AND CYTOKININ METABOLIC CONJUGATION IN VITRO

Václav Motyka

Abstract

Shoot cultures of the essential oil bearing plant Artemisia alba Turra (Asteraceae) were studied with the aim to elaborate the effect of in vitro rooting on cytokinin (CK) conjugation and chloroplast architecture in vitro. For this purpose, two in vitro morphotypes were induced ? (1) the root developing morphotype on plant growth regulator-free as well as on auxin indole-3-butyric acid (IBA)-containing media and (2) the root suppressed morphotype, obtained by a combination of IBA with CK N6-benzyladenine (BA). Endogenous CK levels were analysed by HPLC-ESI-MS/MS. The thylakoid membrane samples were prepared from 1-hour dark- and ice-cold adapted plants. Thylakoid imaging was done by a NanoScopeV system, Bruker Inc. atomic force microscope in a tapping mode in air. In all of the in vitro samples the overall levels of cis-zeatin-type CKs generally significantly exceeded those of trans-zeatin types ? the tendency being more pronounced for aerial samples, and especially for the aerials of the root suppressed morphotype. Further analysis showed that CK N- and O-glucoconjugation patterns were considerably affected by morphogenetic changes. Root suppression and especially callusogenesis were established as a factor causing a drop of N-glucosylation in both aerial and underground samples. In contrast, O-glucosylation was enhanced in both above- and underground tissues of the root suppressed plants. As N- and O-glucosylation represent respective deactivation and storage pathways in CK metabolism, the lack of root formation and enhanced callusogenesis seem to be associated with a reduced metabolic inactivation of CKs and/or increased formation of a CK ?reserve? pool. Marked alteration of plastid morphology was observed in samples with suppressed rooting. It is well known that biogenesis of trans-zeatin-type CKs in plant cells is spatially bound to plastids, while formation of cis-zeatin-type CKs is compartmented in the cytosol. The observed dependencies suggest an interplay between cis- and transzeatins and also among other particular CK forms in A. alba plants cultured in vitro via possible moderation of chloroplast structure.

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