Overexpressing AtCKX1 in Potato Plants grown In Vitro: The Effects on Cytokinin Composition and Tuberization

Endogenous levels of cytokinins, indole-3-acetic acid and abscisic acid in in vitro grown potato: A contribution to potato hormonomics

“…Phytohormones have been considered major players in regulating tuberisation. Gibberellins have been the first group of hormones shown to be importantly involved in tuberisation 38 , but in the recent years growing attention has been paid also to other groups of phytohormones, primarily CKs and auxins [18][19][20][21][22][23] . It has been suggested that endogenous bioactive CKs affect tuber induction, as CK-deficient potato plants overexpressing genes for cytokinin oxidase/dehydrogenase, an enzyme involved in CK catabolism, were able to undergo tuberisation before the 30 th day of growth in "long days" (16 h light/8 h darkness photoperiod), which never happens in wild-type plants 22,23 .…”

“…Gibberellins have been the first group of hormones shown to be importantly involved in tuberisation 38 , but in the recent years growing attention has been paid also to other groups of phytohormones, primarily CKs and auxins [18][19][20][21][22][23] . It has been suggested that endogenous bioactive CKs affect tuber induction, as CK-deficient potato plants overexpressing genes for cytokinin oxidase/dehydrogenase, an enzyme involved in CK catabolism, were able to undergo tuberisation before the 30 th day of growth in "long days" (16 h light/8 h darkness photoperiod), which never happens in wild-type plants 22,23 . The recent increase in research interest for CKs and auxins in potato and their supposed role in tuberisation has resulted in novel developments in potato physiology, most notably the identification of the three CK receptor genes in diploid Phureja potato (orthologous to the three CK receptor genes of Arabidopsis), and cloning and characterisation of the six receptor genes in the autotetraploid cultivar Désirée 39 .…”

“…5) suggests that roots are the primary CK storage site in potato. It has been suggested that O-glucosylation, as well as N-glucosylation and possibly O-xylosylation, may be activated as a protective mechanism against CK degradation in potato plants that overexpress the genes for cytokinin oxidase/dehydrogenase [21][22][23] , thus underlining the biological importance of O-glucosides for maintaining hormonal homeostasis in potato.…”

“…There is growing research interest for CK physiology in potato (Solanum tuberosum L.) due to numerous evidence for the involvement of CKs in the commercially important process of tuberisation [18][19][20][21][22][23] . A number of reports containing measurements of phytohormones in various tissues of potato plants grown in various conditions (in vitro, greenhouse) have been published so far 22,[24][25][26][27][28][29][30][31][32][33] .…”

TransgenicAtCKXCentaury Plants GrownIn Vitro

“…Regardless of this, overexpression of AtCKX genes did not contribute to lowered total CKs content in transgenic centaury plants but rather to an alteration in the spectrum of particular CK types. In analogy, transgenic potato plants overexpressing AtCKX genes were not found to show decreased total endogenous CK contents while bioactive CK forms were predominantly reduced [82,83]. Accordingly, although enhanced CKX activity results in more substantial CK degradation in plant tissues it might simultaneously serve as an indirect signal for the plant cell to intensify the biosynthesis of CKs.…”