Combination of high sucrose concentration with exogenuous cytokinins affects endogenous phytohormone profiles of kohlrabi seedling explants during de novo organogenesis

Abstract

Fluctuations in local phytohormone levels are considered to be important for initiation of developmental events in the process of plant organogenesis. Simultaneously, sugars as signaling molecules affect plant metabolism and growth, potentially interacting with hormonal regulation. Thus, the aim of presented study was to see whether there were any changes in cytokinin (CK) homeostasis in 4 different stages (T1-T4) during de novo shoot organogenesis of kohlrabi (Brassica oleracea var. gongylodes cv. Vienna Purple) seedlings under the influence of exogenous CKs, trans-zeatin (transZ) and thidiazuron (TDZ), combined with high sucrose concentration. Explants grown on CK-free medium with 3% sucrose were used as control. Generally, analysis of variance showed statistically significant impact of CK treatment and sucrose concentration, as well as their interaction in all investigated stages, including seedling development before calli formation (T1 and T2), calli formation (T3) and when de novo shoots occurred (T4). The obtained CK profiles exposed remarkable increase in total CK levels in samples treated with transZ, particularly when 9% sucrose was used in nutrition medium, reaching up to 50 000 pmol/g FW. This trend was observed for all CK physiological and structural groups. On the other hand, application of a synthetic urea-type CK, TDZ, contributed to little or no increase in the endogenous CK levels regardless the sucrose concentration. Our results demonstrated that phytohormones metabolism may be triggered by sucrose signaling in kohlrabi shoot organogenesis.