Cytokinins (CKs) are a chemically diverse class of plant growth regulators, exhibiting wide-ranging actions on plant growth and development, hence their exploitation in agriculture for crop improvement and management. Their coordinated regulatory effects and cross-talk interactions with other phytohormones and signaling networks are highly sophisticated, eliciting and controlling varied biological processes at the cellular to organismal levels. In this review, we briefly introduce the mode of action and general molecular biological effects of naturally occurring CKs before highlighting the great variability in the response of fruit crops to CK-based innovations. We present a comprehensive compilation of research linked to the application of CKs in non-model crop species in different phases of fruit production and management. By doing so, it is clear that the effects of CKs on fruit set, development, maturation, and ripening are not necessarily generic, even for cultivars within the same species, illustrating the magnitude of yet unknown intricate biochemical and genetic mechanisms regulating these processes in different fruit crops. Current approaches using genomic-to-metabolomic analysis are providing new insights into the in planta mechanisms of CKs, pinpointing the underlying CK-derived actions that may serve as potential targets for improving crop-specific traits and the development of new solutions for the preharvest and postharvest management of fruit crops. Where information is available, CK molecular biology is discussed in the context of its present and future implications in the applications of CKs to fruits of horticultural significance.

• Keywords
• abiotic stress, biotechnology, food security, micropropagation, phytohormones, plant growth regulators, postharvest, quality attributes, shoot proliferation, somatic embryogenesis,
• MeSH
• Cytokinins chemistry   metabolism   pharmacology   MeSH
• Molecular Structure MeSH
• Fruit drug effects   growth & development   metabolism   MeSH
• Plant Growth Regulators chemistry   metabolism   pharmacology   MeSH
• Plants drug effects   metabolism   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Cytokinins MeSH
• Plant Growth Regulators MeSH

BACKGROUND: De-etiolation is the switch from skoto- to photomorphogenesis, enabling the heterotrophic etiolated seedling to develop into an autotrophic plant. Upon exposure to blue light (BL), reduction of hypocotyl growth rate occurs in two phases: a rapid inhibition mediated by phototropin 1 (PHOT1) within the first 30-40 min of illumination, followed by the cryptochrome 1 (CRY1)-controlled establishment of the steady-state growth rate. Although some information is available for CRY1-mediated de-etiolation, less attention has been given to the PHOT1 phase of de-etiolation. RESULTS: We generated a subtracted cDNA library using the suppression subtractive hybridization method to investigate the molecular mechanisms of BL-induced de-etiolation in tomato (Solanum lycopersicum L.), an economically important crop. We focused our interest on the first 30 min following the exposure to BL when PHOT1 is required to induce the process. Our library generated 152 expressed sequence tags that were found to be rapidly accumulated upon exposure to BL and consequently potentially regulated by PHOT1. Annotation revealed that biological functions such as modification of chromatin structure, cell wall modification, and transcription/translation comprise an important part of events contributing to the establishment of photomorphogenesis in young tomato seedlings. Our conclusions based on bioinformatics data were supported by qRT-PCR analyses the specific investigation of V-H(+)-ATPase during de-etiolation in tomato. CONCLUSIONS: Our study provides the first report dealing with understanding the PHOT1-mediated phase of de-etiolation. Using subtractive cDNA library, we were able to identify important regulatory mechanisms. The profound induction of transcription/translation, as well as modification of chromatin structure, is relevant in regard to the fact that the entry into photomorphogenesis is based on a deep reprograming of the cell. Also, we postulated that BL restrains the cell expansion by the rapid modification of the cell wall.

• Keywords
• Blue light, De-etiolation, Suppression subtractive hybridization, Tomato (Solanum lycopersicum L.),
• MeSH
• Chromatin ultrastructure   MeSH
• Etiolation genetics   MeSH
• Phototropins physiology   MeSH
• Gene Library MeSH
• Gene Regulatory Networks MeSH
• Hypocotyl growth & development   MeSH
• Gene Expression Regulation, Plant MeSH
• Seedlings genetics   growth & development   MeSH
• Solanum lycopersicum genetics   growth & development   MeSH
• Light * MeSH
• Up-Regulation MeSH
• Vacuolar Proton-Translocating ATPases genetics   physiology   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Chromatin MeSH
• Phototropins MeSH
• Vacuolar Proton-Translocating ATPases MeSH