Dark-induced growth (skotomorphogenesis) is primarily characterized by rapid elongation of the hypocotyl. We have studied the role of abscisic acid (ABA) during the development of young tomato (Solanum lycopersicum L.) seedlings. We observed that ABA deficiency caused a reduction in hypocotyl growth at the level of cell elongation and that the growth in ABA-deficient plants could be improved by treatment with exogenous ABA, through which the plants show a concentration dependent response. In addition, ABA accumulated in dark-grown tomato seedlings that grew rapidly, whereas seedlings grown under blue light exhibited low growth rates and accumulated less ABA. We demonstrated that ABA promotes DNA endoreduplication by enhancing the expression of the genes encoding inhibitors of cyclin-dependent kinases SlKRP1 and SlKRP3 and by reducing cytokinin levels. These data were supported by the expression analysis of the genes which encode enzymes involved in ABA and CK metabolism. Our results show that ABA is essential for the process of hypocotyl elongation and that appropriate control of the endogenous level of ABA is required in order to drive the growth of etiolated seedlings.

• MeSH
• Cyclin-Dependent Kinases antagonists & inhibitors   MeSH
• Cytokinins biosynthesis   metabolism   MeSH
• Endoreduplication radiation effects   MeSH
• Homeostasis radiation effects   MeSH
• Hypocotyl cytology   growth & development   metabolism   radiation effects   MeSH
• Protein Kinase Inhibitors pharmacology   MeSH
• Germination drug effects   radiation effects   MeSH
• Abscisic Acid metabolism   MeSH
• Solanum lycopersicum cytology   growth & development   metabolism   radiation effects   MeSH
• Darkness * MeSH
• Plant Development drug effects   radiation effects   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

Light is one of the most important factor influencing plant growth and development all through their life cycle. One of the well-known light-regulated processes is de-etiolation, i.e. the switch from skotomorphogenesis to photomorphogenesis. The hormones cytokinins (CKs) play an important role during the establishment of photomorphogenesis as exogenous CKs induced photomorphogenesis of dark-grown seedlings. Most of the studies are conducted on the plant model Arabidopsis, but no or few information are available for important crop species, such as tomato (Solanum lycopersicum L.). In our study, we analyzed for the first time the endogenous CKs content in tomato hypocotyls during skotomorphogenesis, photomorphogenesis and de-etiolation. For this purpose, two tomato genotypes were used: cv. Rutgers (wild-type; WT) and its corresponding mutant (7B-1) affected in its responses to blue light (BL). Using physiological and molecular approaches, we identified that the skotomorphogenesis is characterized by an endoreduplication-mediated cell expansion, which is inhibited upon BL exposure as seen by the accumulation of trancripts encoding CycD3, key regulators of the cell cycle. Our study showed for the first time that iP (isopentenyladenine) is the CK accumulated in the tomato hypocotyl upon BL exposure, suggesting its specific role in photomorphogenesis. This result was supported by physiological experiments and gene expression data. We propose a common model to explain the role and the relationship between CKs, namely iP, and endoreduplication during de-etiolation and photomorphogenesis.

• MeSH
• Cell Cycle drug effects   genetics   MeSH
• Cyclin D3 genetics   metabolism   MeSH
• Cytokinins metabolism   MeSH
• Endoreduplication physiology   radiation effects   MeSH
• Phylogeny MeSH
• Hypocotyl physiology   radiation effects   MeSH
• Isopentenyladenosine metabolism   MeSH
• Morphogenesis physiology   radiation effects   MeSH
• Ploidies MeSH
• Plant Proteins genetics   metabolism   MeSH
• Seedlings physiology   radiation effects   MeSH
• Solanum lycopersicum physiology   radiation effects   MeSH
• Light MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH