Gibberellin

[3] All known gibberellins are diterpenoid acids synthesized by the terpenoid pathway in plastids and then modified in the endoplasmic reticulum and cytosol until they reach their biologically active form.[8] The presence of GA1 in various plant species suggests that it is a common bioactive GA.[9] Gibberellins are involved in the natural process of breaking dormancy and other aspects of germination.Before the photosynthetic apparatus develops sufficiently in the early stages of germination, the seed reserves of starch nourish the seedling.[10] Gibberellins in the seed embryo are believed to signal starch hydrolysis through inducing the synthesis of the enzyme α-amylase in the aleurone cells.[11] In this pathway, bioactive GA is produced from trans-geranylgeranyl diphosphate (GGDP), with the participation of three classes of enzymes: terpene syntheses (TPSs), cytochrome P450 monooxygenases (P450s), and 2-oxoglutarate–dependent dioxygenases (2ODDs).[8] The null alleles of the genes encoding CPS, KS, and KO result in GA-deficient Arabidopsis dwarves.[41] Recent evidence suggests fluctuations in GA concentration influence light-regulated seed germination, photomorphogenesis during de-etiolation, and photoperiod regulation of stem elongation and flowering.[42] Bioactive GAs and abscisic acid (ABA) levels have an inverse relationship and regulate seed development and germination.[43][44] Levels of FUS3, an Arabidopsis transcription factor, are upregulated by ABA and downregulated by Giberellins, which suggests that there is a regulation loop that establishes the balance of Gibberellins and Abscisic Acid.In the early 1990s, there were several lines of evidence that suggested the existence of a GA receptor in oat seeds located at the plasma membrane.PIFs are transcription factors that negatively regulate light signalling and are strong promoters of elongation growth.[53] It was later found that DELLAs repress a large number of other transcription factors, among which are positive regulators of auxin, brassinosteroid and ethylene signalling.PFDs are molecular chaperones (they assist in the folding of other proteins) that work in the cytosol, but when DELLAs bind to them are restricted to the nucleus.An important function of PFDs is to assist in the folding of β-tubulin, a vital component of the cytoskeleton in the form of microtubules.As such, in the absence of Gibberellins (high level of DELLA proteins), PFDs reduce its activity, leading to a lower cellular pool of β-tubulin.
1. Shows a plant lacking gibberellins, and which and has an internode length of "0" as well as being a dwarf plant. 2. Shows an average plant with a moderate amount of gibberellins, and an average internode length. 3. Shows a plant with a large amount of gibberellins and so has a much longer internode length, because gibberellins promote cell division in the stem.
GA-GID1-DELLA signal pathway: In the absence of GA, DELLA proteins bind to and inhibit transcription factors (TFs) and prefoldins (PFDs). When GA is present, GID1 triggers the degradation of DELLAs and releases the TFs and PFDs.
plant hormonesdevelopmental processesgerminationdormancyfloweringflowersenescenceselective breedinggreen revolutionplastidsendoplasmic reticulumcytosolGibberellic acidlactoneHydroxylationinternodestarchglucoseendospermhydrolysisamylasescutellumtranscriptioncalciumcalmodulinmethylerythritol phosphatetrans-geranylgeranyl diphosphatecytochrome P450 monooxygenases2-oxoglutarate–dependent dioxygenasesent-copalyl diphosphate synthaseent-kaurene synthaseent-kaurene oxidaseent-kaurenoic acident-kaurenoic acid oxidaseArabidopsissignal transductionGibberella fujikuroisolid-state fermentationphotomorphogenesisde-etiolationphotoperiodabscisic acidplasma membranebioactiveaspartateglutamateleucinealanineamino acid codeF-box proteinscatalyseubiquitin26S-proteosometranscription factorsbrassinosteroidethylenechaperonesnucleusβ-tubulincytoskeletonmicrotubulesmembrane vesicleshormone transportersPIN proteinscell membraneBibcodeCampbell NAuxinsBrassinosteroidsCytokinins24-EpibrassinolideFlorigenJasmonatesKarrikinsPlant peptide hormonesPolyamineSalicylic acidStrigolactones