Cytokinins (CKs) play a crucial role in various phases of plant growth and development, but the basic molecular mechanisms of their biosynthesis and signal transduction only recently became clear. The progress was achieved by identifying a series of key genes encoding enzymes and proteins controlling critical steps in biosynthesis, translocation, and signaling. Basic schemes for CK homeostasis and root/shoot communication at the whole-plant level can now be devised. This review summarizes recent findings on the relationship between CK structural variation and activity, distinct features in CK biosynthesis between higher plants and Agrobacterium infected plants, CK translocation at whole-plant and cellular levels, and CKs as signaling molecules for nutrient status via root-shoot communication.

CYTOKININS: Activity, Biosynthesis, and Translocation

■ Abstract Cytokinins are structurally diverse and biologically versatile. The chemistry and physiology of cytokinin have been studied extensively, but the regulation of cytokinin biosynthesis, metabolism, and signal transduction is still largely undefined. Recent advances in cloning metabolic genes and identifying putative receptors portend more rapid progress based on molecular techniques. This review centers on cytokinin metabolism with connecting discussions on biosynthesis and signal transduction. Important findings are summarized with emphasis on metabolic enzymes and genes. Based on the information generated to date, implications and future research directions are presented.

Cytokinin metabolism and action

▪ Abstract Plant growth retardants are applied in agronomic and horticultural crops to reduce unwanted longitudinal shoot growth without lowering plant productivity. Most growth retardants act by inhibiting gibberellin (GA) biosynthesis. To date, four different types of such inhibitors are known: (a) Onium compounds, such as chlormequat chloride, mepiquat chloride, chlorphonium, and AMO-1618, which block the cyclases copalyl-diphosphate synthase and ent-kaurene synthase involved in the early steps of GA metabolism. (b) Compounds with an N-containing heterocycle, e.g. ancymidol, flurprimidol, tetcyclacis, paclobutrazol, uniconazole-P, and inabenfide. These retardants block cytochrome P450-dependent monooxygenases, thereby inhibiting oxidation of ent-kaurene into ent-kaurenoic acid. (c) Structural mimics of 2-oxoglutaric acid, which is the co-substrate of dioxygenases that catalyze late steps of GA formation. Acylcyclohexanediones, e.g. prohexadione-Ca and trinexapac-ethyl and daminozide, block particularly...

/pdf/growth-retardants-effects-on-gibberellin-biosynthesis-and-13rt99n3qy.pdf

GROWTH RETARDANTS: Effects on Gibberellin Biosynthesis and Other Metabolic Pathways

The rice slender mutant (slr1-1) is caused by a single recessive mutation and results in a constitutive gibberellin (GA) response phenotype. The mutant elongates as if saturated with GAs. In this mutant, (1) elongation was unaffected by an inhibitor of GA biosynthesis, (2) GA-inducible α-amylase was produced by the aleurone layers without gibberellic acid application, and (3) endogenous GA content was lower than in the wild-type plant. These results indicate that the product of the SLR1 gene is an intermediate of the GA signal transduction pathway. SLR1 maps to OsGAI in rice and has significant homology with height-regulating genes, such as RHT-1Da in wheat, D8 in maize, and GAI and RGA in Arabidopsis. The GAI gene family is likely to encode transcriptional factors belonging to the GRAS gene superfamily. DNA sequence analysis revealed that the slr1-1 mutation is a single basepair deletion of the nuclear localization signal domain, resulting in a frameshift mutation that abolishes protein production. Furthermore, introduction of a 6-kb genomic DNA fragment containing the wild-type SLR1 gene into the slr1-1 mutant restored GA sensitivity to normal. These results indicate that the slr1-1 mutant is caused by a loss-of-function mutation of the SLR1 gene, which is an ortholog of GAI, RGA, RHT, and D8. We also succeeded in producing GA-insensitive dwarf rice by transforming wild-type rice with a modified SLR1 gene construct that has a 17–amino acid deletion affecting the DELLA region. Thus, we demonstrate opposite GA response phenotypes depending on the type of mutations in SLR1.

slender Rice, a Constitutive Gibberellin Response Mutant, Is Caused by a Null Mutation of the SLR1 Gene, an Ortholog of the Height-Regulating Gene GAI/RGA/RHT/D8

Plant cells coordinately regulate the expression of nuclear and plastid genes that encode components of the photosynthetic apparatus Nuclear genes that regulate chloroplast development and chloroplast gene expression provide part of this coordinate control There is evidence that information also flows in the opposite direction, from chloroplasts to the nucleus Until now, at least three different signalling pathways have been identified that originate in the plastid and control nuclear gene expression but the molecular nature of these signals has remained unknown Here we show that the tetrapyrrole intermediate Mg-protoporphyrin (Mg-ProtoIX) acts as a signalling molecule in one of the signalling pathways between the chloroplast and nucleus Accumulation of Mg-ProtoIX is both necessary and sufficient to regulate the expression of many nuclear genes encoding chloroplastic proteins associated with photosynthesis

Chloroplast to nucleus communication triggered by accumulation of Mg-protoporphyrinIX

Sur la base des resultats obtenus on discute les effets inhibiteurs du S-3307 sur les plantes intactes en termes d'effets inhibiteurs sur la biosynthese des gibberellines

Studies of sites of action of a new plant growth retardant (E)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (S-3307) and comparative effects of its stereoisomers in a cell-free system from Cucurbita maxima

Effects of a New Plant Growth Retardant (E)-1-(4-Chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (S-3307) on the Growth and Gibberellin Content of Rice Plants

Levels of IAA, Cytokinins, ABA and Ethylene in Rice Plants as Affected by a Gibberellin Biosynthesis Inhibitor, Uniconazole-P.

METHOD FOR CONTROLLING THE GROWTH OF PLANTS ABSTRACT OF THE DISCLOSURE A method for controlling the growth of plants, characterized by applying a plant growth regulator containing as active ingredient a benzenesulfonamide derivative represented by the general formula, wherein X is a halogen atom, an alkyl group having 1 to 5 carbon atoms, a nitro group, an amino group, an alkoxy group having 1 to 5 carbon atoms, an alkyl-thio group having 1 to 5 carbon atoms, an alkylsulfonyl group having 1 to 5 carbon atoms, or a group of the formula R3CONH- (where R3 is an alkyl group having 1 to 5 carbon atoms); n is an integer of 0 to 5; R1 is hydrogen, an alkyl group having 1 to 5 carbon atoms, a phenyl group, a group of the formula -(A)-COOR4 [where R4 is hydrogen, an alkyl group having 1 to 5 carbon atoms, a cation such as Na+, K+, ammonium or a quaternary ammonium ion, and (A) is a group of the formula -(CH2)m- (where m is an integer of 1 to 3), or a group of the formula (where R5 and R6 are individually hydrogen or an alkyl group having 1 to 5 carbon atoms)]; and R2 is a straight chain, branched chain or alicyclic alkyl group having 1 to 15 carbon atoms, a hydroxyalkyl group having 1 to 5 carbon atoms, a haloalkyl group having 1 to 5 carbon atoms, a hydroxyl group, an amino-alkyl group having 1 to 5 carbon atoms, a cyano-C1-5-alkyl, an alkenyl group having 2 to 5 carbon atoms, a C1-5-alkoxy-C5-5-alkyl group, a sulfo-alkyl group having 1 to 5 carbon atoms, a phenyl-substituted alkyl group having 1 to 5 carbon atoms, or a group of the formula -(A)-COOR4 (where R4 and (A) are as defined above), when R1 is hydrogen; is a hydroxyalkyl group having 1 to 5 carbon atoms, a group of the formula -(A)-COOR4 (where R4 and (A) are as defined above), a group of the formula -(B)-OOCR7[where R7 is a phenyl group or an alkyl group having 1 to 5 carbon atoms, and (B) is a group of the formula (CH2)j- (where j is an integer of 1 to 3), or a group of the formula (where R5 and R6 are as defined above)], when R1 is an alkyl group having 1 to 5 carbon atoms; and is a group of the formula -(A)-COOR4 (where R4 and (A) are as defined above), when R1 is a phenyl group or a group of the formula -(A)-COOR4 (where R4 and (A) are as defined above).

Hiromichi Oshio

Papers

Studies of sites of action of a new plant growth retardant (E)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (S-3307) and comparative effects of its stereoisomers in a cell-free system from Cucurbita maxima

Effects of a New Plant Growth Retardant (E)-1-(4-Chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (S-3307) on the Growth and Gibberellin Content of Rice Plants

Levels of IAA, Cytokinins, ABA and Ethylene in Rice Plants as Affected by a Gibberellin Biosynthesis Inhibitor, Uniconazole-P.

Method for controlling the growth of plants

Diphenylether-like physiological and biochemical actions of S-23142, a novel N-phenyl imide herbicide