Altered cytokinin metabolism affects cytokinin, auxin, and abscisic acid contents in leaves and chloroplasts, and chloroplast ultrastructure in transgenic tobacco

Abstract

Cytokinins (CKs) are involved in the regulation of plant development including plastid differentiation and function. Partial location of CK biosynthetic pathways in plastids suggests the importance of CKs for chloroplast development. The impact of genetically modified CK metabolism on endogenous CK, indole-3-acetic acid, and abscisic acid contents in leaves and isolated intact chloroplasts of Nicotiana tabacum was determined by liquid chromatography/mass spectrometry and two-dimensional high-performance liquid chromatography, and alterations in chloroplast ultrastructure by electron microscopy. Ectopic expression of Sho, a gene encoding a Petunia hybrida isopentenyltransferase, was employed to raise CK levels. The increase in CK levels was lower in chloroplasts than in leaves. CK levels were reduced in leaves of tobacco harbouring a CK oxidase/dehydrogenase gene, AtCKX3. The total CK content also decreased in chloroplasts, but CK phosphate levels were higher than in the wild type. In a transformant overexpressing a maize beta-glucosidase gene, Zm-p60.1, naturally targeted to plastids, a decrease of CK-O-glucosides in chloroplasts was found. In leaves, the changes were not significant. CK-O-glucosides accumulated to very high levels in leaves, but not in chloroplasts, of plants overexpressing a ZOG1 gene, encoding trans-zeatin-O-glucosyltransferase from Phaseolus lunatus. Manipulation of the CK content affected levels of indole-3-acetic and abscisic acid. Chloroplasts of plants constitutively overexpressing Sho displayed ultrastructural alterations including the occasional occurrence of crystalloids and an increased number of plastoglobuli. The other transformants did not exhibit any major differences in chloroplast ultrastructure. The results suggest that plant hormone compartmentation plays an important role in hormone homeostasis and that chloroplasts are rather independent organelles with respect to regulation of CK metabolism.

Exogenous Cytokinin Promotes Epipremnum aureum L. Growth through Enhanced Dry Weight Assimilation rather than through Changes in Partitioning

“…Cytokinins have long been implicated in chlorophyll synthesis [30] although this not always results in an increased concentration in plant tissues [32]. In our experiments, chlorophyll concentration per unit dry weight was unaffected by BAP treatment.…”

“…Apriori, both alternatives appeared as likely since there is abundant experimental or bibliographic support: In our previous paper [3] it was shown that BAP increased E. aureum final leaf size and decreased the phyllochron, but cytokinins are also well known to promote the efficiency of the photosynthetic apparatus [30].…”

Identification of QTLs associated with albino plant formation and some new facts concerning green versus albino ratio determinants in triticale (×Triticosecale Wittm.) anther culture

“…It is well known that chloroplast biogenesis is controlled by cytokinins (CKs) and exogenously applied CKs can stimulate development of chloroplasts from proplastids, amyloplasts, and etioplasts (after Polanska et al 2007). It has been revealed that this effect was mediated by up-regulation of the expression of some plastid-related genes, both of plastid and nuclear origin.…”

Interspecies hormonal control of host root morphology by parasitic plants

“…5). Overexpression of AtCKX3 reduces cytokinin levels in a distant relative of Phtheirospermum, Nicotiana tabacum (27), and caused various cytokinin-deficient phenotypes in Arabidopsis and N. tabacum (11,28). Thus, we reasoned that overexpressing AtCKX3 in Phtheirospermum would also reduce parasite cytokinin levels.…”