Changes in cis‐zeatin and cis‐zeatin riboside levels and biological activity during potato tuber dormancy

Abstract

20°C) prior to use, the rise in endogenous cis-Z was less The effects of postharvest storage duration and temperature on endogenous cis-zeatin (cis-Z) and cis-zeatin riboside (cis-dramatic and more protracted; increasing twofold after 53 days of storage. No change in cis-Z riboside content was ZR) levels in potato (Solanum tuberosum L.) tubers were observed in these tubers during this period. Dose-response determined in relation to tuber bud dormancy. The tubers used in these studies were completely dormant for at least 81 studies using either cis-Z or trans-Z demonstrated a time-dependent increase in cytokinin sensitivity during postharvest days of storage. Thereafter, tuber bud dormancy diminished storage. Immediately after harvest, dormant tubers were in-gradually and after 165 days of postharvest storage, the tubers were completely non-dormant. Immediately after har-sensitive to both zeatin isomers. Thereafter, tubers exhibited a dose-dependent increase in premature sprouting following vest, endogenous levels of cis-Z and cis-ZR were approxiinjection with either cytokinin isomer. After injection into mately 25 pmol (g fresh weight) − 1 and 8 pmol (g fresh dormant tubers, cis-[8-14 C]-zeatin was metabolized primarily weight) − 1 , respectively. In tubers exiting dormancy but stored at a growth-inhibiting temperature (3°C), endogenous to adenine/adenosine and cis-Z riboside. Seven days after injection, less than 10% of the recovered radioactivity was levels of cis-Z rose over threefold after 25 days of storage associated with trans-ZR. These results are consistent with a and remained elevated for the duration of the study. Levels of role for endogenous cis-Z (and its derivatives) in the regula-cis-ZR remained essentially constant during this same period. tion of potato tuber dormancy. In tubers transferred to a growth permissive temperature stored crop and result in financial losses to producers and processors in excess of several hundred million dollars annually.At the cellular level, tuber meristem dormancy is a result of an inhibition of cell division (Macdonald and Osborne 1988). Meristematic cells in the tuber buds (eyes) are arrested in the G 1 -phase of the cell cycle prior to the onset of DNA replication (Campbell et al. 1996). The resumption of bud growth following the termination of dormancy is accompanied by a large increase in DNA synthesis and in the number of cells traversing the cell cycle.The molecular processes regulating meristem dormancy in plants remain unknown (see Bewley 1997). However, there

Is dormancy breaking of potato tubers the reverse of tuber initiation?

“…In contrast, Suttle & Banowetz (2000) discussed cis-isomers. The question arises whether both isomeric forms are biologically relevant.…”

“…The question arises whether both isomeric forms are biologically relevant. As Suttle & Banowetz (2000) suggest; 'it is possible that only one of the two isomeric forms is biologically important or, alternatively, it is possible that both have a role in dormancy termination either directly as cytokinin agonists or indirectly in a precursor/product relationship'.…”

“…Suttle (1998b) also found increases in bioactive cytokinin content in potato tuber buds prior to the loss of dormancy. More recently, Suttle & Banowetz (2000) determined the endogenous levels of cis-zeatin (cis-Z) and ciszeatin riboside (cis-ZR). They found that the level of cis-Z increased already at day 25 during the 81 days of dormancy and remained constant thereafter.…”

O-Glucosylation of cis-Zeatin in Maize. Characterization of Genes, Enzymes, and Endogenous Cytokinins

“…However, in rice (Oryza sativa), another monocot, O-glucosyl-ciszeatin and its riboside were found (Takagi et al, 1989). In fact, the number of species in which ciszeatin was detected has increased steadily over the years and now includes potato (Solanum tuberosum; Mauk and Langille, 1978;Suttle and Banowetz, 2000), hops (Watanabe et al, 1981), sweet potato (Ipomoea batatas; Hashizumi et al, 1982), rice (Takagi et al, 1985), wheat (Triticum aestivum; Parker et al, 1989), oats (Avena sativa; Parker et al, 1989), Mercurialis spp. (Durand and Durand, 1994), chickpea (Emery et al, 1998), lupins (Emery et al, 2000), and tobacco (Nicotiana tabacum; Dobrev et al, 2002).…”

Cytokinin Differences in In Vitro Cultures and Inflorescences from Normal and Mantled Oil Palm (Elaeis guineensis Jacq.)

“…In potato, rice, and seeds of oats and lucerne, for example, ciszeatin (cZ) is the dominant cytokinin species, whereas in maize seeds, the DZ-type is predominant (Takagi and others 1985;Suttle and Banowetz 2000;Veach and others 2003;Vyroubalova and others 2009;Stirk and others 2012). The present study found that tZs and iPs were the predominant cytokinins in in vitro oil palm cultures, whereas in inflorescences, only tZ cytokinins were predominant.…”