PERAN HORMON PADA PERTUMBUHAN DAN PERKEMBANGAN TUMBUHAN

Why do plants need hormones? Hormones enable plants to:Respond to environmental factors and changesDirect developmental processes

Why do plants need hormones?PathogensParasitesHumidityTemperatureLightToxinsInsectsOxygenStress

Konsep dan definisi hormonHormon tumbuhan:* senyawa yang disintesis secara alami oleh tumbuhan* transport* respon * efektif pada konsentrasi rendah (memacu atau menghambat pertumbuhan)

Plant hormones are chemical messengersHormone synthesisMessageFaktor lingkungan sangat berpengaruhHormon : senyawa yang mengintegrasi sinyal lingkungan dan mendistribusikannya ke bagian tubuh tumbuhan

Proses-proses yang dipengaruhi hormon:* tumbuh* diferensiasi* perkembangan (note: membuka / menutupnya stomata juga dipengaruhi hormon)

Hormone do not act alone but in conjunction, or in oposition, to each other

The final condition of growth or development represents the net effect of a hormonal balance

Hormon tumbuhan merupakan senyawa yang relatif sederhanaPerlu spesifik reseptor yang dapat mengikat senyawa tersebutKeberadaan satu jenis hormon seringkali mempengaruhi sintesis atau aksi hormon yang lain

Signal-transduction pathways in plants

Classes HormonesFive classes are identifiedAuxinsGibberellinsCytokininsEthyleneAbscisic AcidNew hormones:Brassinosteroid Jasmonic acidSalicylic acidPolyamine

AuxinPrimary form is Indole acetic acid (IAA)Photo-, Gravi-, and Thigmotropisms come about in large part due to auxin effectsRegulate growth primarily by promoting cell elongation with some differentiation.

Auxin production and transportProduced in shoot apical tips, leaves, & seedsMoves from tip to baseMoves primarily through parenchyma cells surrounding vascular tissue

Polar transport of Auxin

Plant tropismsGrowth in a particular direction in response to an external stimulusResponse to gravity is called gravitropismTo light is phototropismTo touch is thigmotropismResponses may be positive or negative

Phototropi mechanism

GravitropismRoot & shoot differential growth in response to gravityAuxin in higher amounts on lower side of organRoots: negative responseRoot more sensitive to auxin - inhibits elongation

ThigmomorphogenesisRubbing the stems of young plants a couple of times dailyResults in plants that are shorter than controls

Dominansi apikalProduksi & transport Auxin dari pucuk menghambat pertumbuhan tunas lateralPemangkasan tunas pucuk akan memacu pertumbuhan tunas lateralControl

Leaf senescence

Other effects of auxinStimulates development of fruitCan stimulate lateral root formationMay stimulate adventitious root formation in stems

10-11 10-9 10-7 10-5 10-3 10-1 Molar concentration of IAApromotioninhibitionakarbatang

GibberellinsTranslocated in xylem & pholemFormed in young leaves, apical tips, embryoEffectsBoltingCan overcome dwarfing in some plantsStimulates flowering in some plantsAffects fruit developmentStimulates germination of seedsGA1

Contoh efek GiberelinPertumbuhan memanjang pada tanaman kubis Treated once/week for 2 months

Dwarf PeaControlGibberillin added

Fisiologi TumbuhanEfek Giberelin

Cell elongationSeed germinationFlower inductionBreaking dormancy

Peran / Fungsi giberelin

SitokininEfek Sitokinin:

pembelahan sel, morfogenesis, pertumbuhan tunas lateral, pembentangan daun, menunda penuaan daun

sitokininEffect of cytokinin application on leaf senescenceStimulates cell divisionLateral bud developmentDelays senescence and promotes nutrient uptakeRost et al., 1998

Senescence pada daun tembakau transgenikTanaman sebelah kiri disisipi gen yangberperan dalam produksi sitokinin dan tetap Aktif sepanjang siklus hidup tumbuhan

Aplikasi sitokinin Control surfactan 0.5% sitokinin 0.5% sit + surfactan

Asam absisat Mula-mula dinamakan : abscisin II (absisi pada kapas) dormin (dormansi tunas)

aplikasi ABA kebanyakan bersifat menghambat pertumbuhan

ABA sebagai promoter : sintesis protein sebagai cadangan makanan dalam biji

Fisiologi TumbuhanAsam absisatABA :Bersifat menghambat pertumbuhanMenginduksi & mempertahankan dormansi biji dan tunasSintesis dipacu dengan adanya stressABA deficient mutant : viviparyABA juga mengontrol membuka / menutupnya stomata

Asam absisatSintesis ABA : dari gliseraldehid-3-fosfat melalui isopentenyl difosfat dan karotenoid

Letak sintesis : akar, daun-daun yang tua (akibat cekaman air), biji

Transport : dari akar (melalui xilem) dari daun (melalui floem)

Asam absisatEfek ABA:Menutupnya stomataMenghambat pertumbuhan tunasMenghambat efek giberelin ( pada sintesis a-amylase)Menginduksi dan mempertahankan dormansi bijiBerperan dalam pertahanan terhadap serangan insekta (melalui kemampuan ABA menginduksi transkripsi gen proteinase inhibitor)

Ethylene (C2H4)

Gas - diffuses through tissuesStimulates abscission and fruit ripeningUsed in commercial ripening for bananas & green picked fruitInvolved in leaf abscission & flower senescencePrimarily synthesized in response to stress

Karakteristik etilenSintesis etilen terpacu dengan adanya sedikit etilenLuka pada tanaman menginduksi sintesis etilenSatu apel / pisang busuk dapat memacu pembusukan sekeranjang apel / pisang

EtilenEfek Etilen:

Triple responsePelepasan dormansiPembentukan akar adventifMemacu pengguguran daunMemacu kelayuan bunga

*****The term auxin is derived from the Greek word auxein which means to grow. Compounds are generally considered auxins if they can be characterized by their ability to induce cell elongation in stems and otherwise resemble indoleacetic acid (the first auxin isolated) in physiological activity. Auxins usually affect other processes in addition to cell elongation of stem cells but this characteristic is considered critical of all auxins and thus "helps" define the hormone. Although there is only one naturally occurring auxin: indole-3-acetic acid (IAA: chemically related to the amino acid tryptophan) there are many synthetic auxins********With over 80 analogs identified, gibberellins are the largest hormone grouping . They are used commercially to break dormancy in seeds which will not germinate readily,to promote fruit setting in a number of plants, including the production of parthenocarpic ( seedless) varieties and to produce dwarf plants, and in the beer industry...Discovery: Kurosawa, a Japanese botanist, discovered gibberellin while investigating the rice foolish seedling disease in which spindly seedlings are formed due to GA like compounds produced by the fungus ( Gibberella fujikuroi) infecting the plant.( see text for more information) . Extensive Growth --Produced by roots and young leaves, it increases growth by both division and elongation; promotes elongation of dwarf mutants. It stimulates shoot elongation even in mature regions of trees & shrubs Juvenility -- juvenile stages of some plants have different shaped leaves than the adult stage. Gibberellins help determine whether a particular part of a plant is juvenile or adult. An example to further explain this is that the buds of adult branches grow into adult branches, but if treated with gibberellin it grows into juvenile branches. Flowering -- Biennial + Gibberellin ---> Annual. Biennials when treated with gibberellin give flowers and fruits in their first year instead of the usual two years. Parthenocarpic -- stimulates pollen germination and growth. results in larger fruits and even bigger flowers. Fruit formation -- increases size of fruits. Seed Germination -- breaks dormancy of certain seeds. This is used in beer industry....yeast need a large supply of malt sugars from barley to ferment....As the seed imbibes water the embryo produces GAGA attaches to a protein receptor which sends a signal to a transduction pathway to switch on particular genes --> m-RNA.Through transcription and translation this leads to synthesis of amylase which then is secreted into the endosperm (stored food reserve)Amylase breaks down starch to glucose units which diffuses to the embryo and are used for plant growth.****Ethylene which promotes tracheid differentiation might repress vessel and fiber differentiation.

The ethylene, which interrupts the longitudinal orientation of the developing regenerative tracheids, is probably involved in the differentiation of radially oriented tracheids in the vascular rays of conifers.*