A new sustainable strategy for medicinal plants protection against stress?

Plants in greenhouses are seldom exposed to UV-B radiation, a natural part of the solar spectrum. UV-B can give broad stress responses and increased resistance to stress, e.g. pathogens and herbivores. UV-B exposure already in the greenhouse may prepare the plants for outdoor conditions. Scots pine (Pinus sylvestris L.) needles were analyzed regarding content of thiobarbituric acid reactive substances (TBARS) (a measure of lipid peroxidation) [1], total phenolic substances [2] and dehydrin gene expression [3]. Stress response in seedlings moved outdoors two months after sowing was compared with control seedlings left in the greenhouse and seedlings moved outdoors but covered by a non-woven fabric. Unprotected seedlings showed increased levels of TBARS and phenolic substances, while covered seedlings were unchanged (Fig. 1). Changed expression of defense related genes is a common response to stress. One dehydrin gene in pine (PsDhn5) was downregulated in unprotected seedlings. The effects on oxidative stress (TBARS) and defense (phenolic substances) is in line with visible stress related symptoms on conifer seedlings when moved outdoors, and could therefore be a tool in development of a new protecting strategy. Downregulation of PsDhn5 fits well with our results showing downregulation of this gene by drought stress. Epigenetic mechanisms play important roles in plant defense induction [4]. Spruce seedlings exposed to UV-B have shown epigenetic changes and increased release of terpenoids with known effects on pine weevil behaviour [5]. This sustainable way of plant protection can be a new strategy for some medicinal plants against biotic and abiotic stress.

Fig. 1: Content of thiobarbituric acid reactive substances (TBARS; lipid peroxidation) and total phenolic substances in two months old pine seedlings 9 days after transfer outdoors from previous greenhouse growth.

Acknowledgements: This publication is the result of the project implementation: Support of establishment, development, and mobility of quality research teams at Charles University, project number CZ.1.07/2.3.00/30.0022, supported by the Education for Competitiveness Operational Programme (ECOP) and co-financed by the European Social Fund and the state budget of the Czech Republic.

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[3] Wachowiak, W. et al. (2009) Tree Genetics & Genomes 5:117 – 132.

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[5] Ohlsson, A.B. et al. (2013) Z. Naturforsch. 68 c: 139 – 147.