Carbohydrates and gibberellins relationship in potato tuberization.

Potato represents the third most important crop worldwide and therefore to understand regulations of tuber onset is crucial from both theoretical and practical points of view. Photosynthesis and related carbohydrate status along with phytohormone balance belong to the essential factors in regulation of plant development including storage organ formation. In our work we used potato (Solanum tuberosum) cv. Lada and its spontaneously tuberizing mutant (ST plants) grown in vitro under low carbohydrate availability (non-inductive conditions). Small plant phenotype and readiness to tuberization of ST plants was, however, not accompanied by lower gibberellins levels, as determined by UHPLC-MS/MS. Therefore, we focused on the other inducing factor, carbohydrate status. Using HPLC, we followed changes in carbohydrate distribution under mixotrophic (2.5% sucrose in medium) and photoautotrophic conditions (no sucrose addition and higher gas and light availability) and observed changes in soluble carbohydrate allocation and starch deposition, favouring basal stem part in mutants. In addition, the determination of tuber-inducing marker gene expressions revealed increased levels of StSP6A in ST leaves. Collectively these data point towards the possibility of two parallel cross-talking pathways (carbohydrate - and gibberellin- dependent ones) with the power of both to outcompete the other one when its signal is for some reason extraordinary strong.