Liquid in vitro culture system allows gradual intensification of osmotic stress in Solanum tuberosum through sorbitol

Abstract

Because of their shallow root system, drought stress is a major problem in potato cultivation. Due to climate change more severe drought periods are expected to occur in the vegetative growth phase of potato growth. Therefore, there is a great need for drought tolerant potato genotypes. Potato responds to drought stress in the field in various ways, including osmoregulation. Osmotic stress can be induced in vitro by adding an osmotic agent and thus lowering the osmotic potential of the medium. In this study, a new, cost-effective in vitro test system is presented, in which the osmotic agent can be gradually added after root formation to prevent an osmotic shock. This is achieved by using sieves as plant holders and liquid medium, which, allows an improved simulation of gradually drying soil. Responses to osmotic stress in four potato genotypes were analysed and an increase in proline under osmotic stress was detected. Moreover, genes of interest that were postulated to be linked to drought stress were shown by quantitative qRT-PCR to be regulated under osmotic stress. Furthermore, we showed that the content of sorbitol, which was used as osmotic agent, was 700- fold higher for ‘Eurostarch’ after seven days under osmotic stress and 1093- fold higher after 14 days, respectively, compared to control plants without sorbitol addition. Therefore, further investigations must show, whether it was taken up through the roots, is metabolised, stored or de novo synthesised by the potato plants. Keypoints The established novel in vitro test system for potato allows gradually increasing stress exposition of rooted plants. Sorbitol seems not an ideal osmotic agent as it is likely taken up.