ABSTRACT
The white dead nettle, Lamium album L., is an herb that has been successfully cultivated under in vitro conditions. The L. album micropropagation system offers a combination of factors (light intensity, temperature, carbon dioxide (CO2) level, humidity) that are limiting for plant growth and bioactive capacity. To get a better understanding of the mechanism of plant acclimation towards environmental changes, we performed a comparative investigation on primary and secondary metabolism in fully expanded L. album leaves during the consecutive growth in in situ, in vitro, and ex vitro conditions. Although the genetic identity was not affected, structural and physiological deviations were observed, and the level of bioactive compounds was modified. During in vitro cultivation, the L. album leaves became thinner with unaffected overall leaf organization, but with a reduced number of palisade mesophyll layers. Structural deviation of the thylakoid membrane system was detected. In addition, the photosystem 2 (PS2) electron transport was retarded, and the plants were more vulnerable to light damage as indicated by the decreased photoprotection ability estimated by fluorescence parameters. The related CO2 assimilation and transpiration rates were subsequently reduced, as were the content of essential oils and phenolics. Transfer of the plants ex vitro did not increase the number of palisade numbers, but the chloroplast structure and PS2 functionality were recovered. Strikingly, the rates of CO2 assimilation and transpiration were increased compared to in situ control plants. While the phenolics content reached normal levels during ex vitro growth, the essential oils remained low. Overall, our study broadens the understanding about the nature of plant responses towards environmental conditions.
Subject(s)
Adaptation, Physiological , Lamiaceae/physiology , Oils, Volatile/metabolism , Photosynthesis/physiology , Photosystem II Protein Complex/metabolism , Plant Oils/metabolism , Carbon Dioxide/metabolism , Chlorophyll/metabolism , Chloroplasts/metabolism , Electron Transport , Flavonoids/metabolism , Fluorescence , Hydroxybenzoates/metabolism , Lamiaceae/genetics , Lamiaceae/radiation effects , Lamiaceae/ultrastructure , Light , Plant Leaves/genetics , Plant Leaves/physiology , Plant Leaves/radiation effects , Plant Leaves/ultrastructure , Plant Transpiration/physiology , Plants, Medicinal , Ploidies , Temperature , Thylakoids/metabolismABSTRACT
Brassinosteroids (BRs) are plant steroid hormones known to positively affect photosynthesis. In this work we investigated the architecture and function of photosynthetic membranes in mature Arabidopsis rosettes of BR gain-of-function (overexpressing the BR receptor BR INSENSITIVE 1 (BRI1), BRI1OE) and loss-of-function (bri1-116 with inactive BRI1 receptor, and constitutive photomorphogenesis and dwarfism (cpd) deficient in BR biosynthesis) mutants. Data from atomic force microscopy, circular dichroism, fluorescence spectroscopy and polarographic determination of oxygen yields revealed major structural (enlarged thylakoids, smaller photosystem II supercomplexes) and functional (strongly inhibited oxygen evolution, reduced photosystem II quantum yield) changes in all the mutants with altered BR response compared to the wild type plants. The recorded thermal dependences showed severe thermal instability of the oxygen yields in the BR mutant plants. Our results suggest that an optimal BR level is required for the normal thylakoid structure and function.
