Plant Physiology

Lecturer:Doc. Ing. Václav Hejnák, Ph.D.

Tel.: 224382514E-mail: hejnak @af.czu.cz

PHYTOHORMONES AND THEIR PHYSIOLOGICAL EFFECT

PHYTOHORMONES AND THEIR PHYTOHORMONES AND THEIR PHYSIOLOGICAL EFFECTPHYSIOLOGICAL EFFECT

Development, growth and differentiation

Control of growth and development

Genetic control of developmentHormonal regulation of developmentEnvironmental regulation of development

The role of hormones in plant development

auxins, gibberellins, cytokinins, abscisic acid, ethylene.

The influence of plant hormone groups on differentcategories of development.

An x indicates a demonstrated effect of that hormone group on one or more aspects of that developmental category. The absence of an xdoes not mean that the hormone is ineffective, only that an effect has not been reported in literature. (Reprinted from G. Hopkins: Introduction to Plant Physiology. John Wiley et Sons, New York, 1995.)

The effects of auxin concentration on the growth of different organs.

Multiple effect of auxinin higher plants.The hormone is formed mainly in the tip of the shoot and is transported from there into the different organs. Following the predetermined competence for auxin, different site react differently with specific processes of growth and differentiation (from Hopkins 1995, after Steward 1964).

Auxin stimulated adventitious root development on American holly (Ilex opaca) cuttings. Row A: Treated with a 0.01% solution of indolebutyric acid solution for 17 hours before being rooted insand. Row B: Untreated controls. (after T.E.Weier et al. 1982, reprinted from G. Hopkins: Introduction to Plant Physiology. John Wiley et Sons, New York, 1995.)

The control of apical dominance by auxin. Experimental material: Field bean (Vicia faba). After removal of the apical terminal bud (a) side buds grow in the lower leaf axils (b). If the cut apical surflace is covered by an agar block containing IAA, lateral buds remain inhibited (c). A control block (without IAA) has no effect (d). IAA is therefore able to replace the end bud with respect to apical dominance. (from Mohr et Schopfer 1995, after Bonner et Galston 1952)

Apical dominance in broadbean (Vicia faba) (A) Control plants. (B) Removal of the stem apex, a source of auxin, promotes axillary bud growth. (C) Dominance can be restored by applying auxin (in lanolin paste) to the cut stem surface. (Reprinted from G. Hopkins: Introduction to Plant Physiology. John Wiley et Sons, New York, 1995.)

Auxin (IAA) and cytokinin (kinetin) as factors limiting mitotic activity and formation of organs in a tissue culture. Experimental material: Explant from stem pith of a tobacco plant (Nicotiana tabacum). Relatively high concentrations of IAA and kinetin lead to the formation of a callus after a few weeks. Development can be redirected to root or shoot formation by either increasing or decreasing the ratio of IAA/kinetin. (from Mohr et Schopfer 1995, after Ray 1963)

Dwarfism in a GA deficiency mutant and its reversal by GA application. Experimental material: Dwarf-5 mutant (D-5/d-5) and wild type of maize (Zea mays). The mutant received in total 250 μg GA3 applied to the apex from the seedling stage at intervals of 2 to 5d. From left to right: Wild type, untreated; wild type, treated; mutant, untreated; mutant, treated. Analysis shows that stunted growthis based on the failure of one gene, which controls the cyclisation of copalylpyrophosphate to ent-kaurene. The phenotypic defect can therefore be reversed by application of ent-kaurene. (after Phinney and West 1960, from Mohr et Schopfer 1995)

The effect of gibberellic acid on dwarf pea. Left: Control, showing reduced internode elongation. Right: Gibberellin treated. Enhanced internode elongation following a foliar-drench with 5 x 10-4 M gibberellin. (after Hopkins 1995)

Gibberellin-stimulated stem growth in a rosette genotype of Brassica napus. Treatments were (from left): 0, 0.5, 1.0, 10.0 ng GA3 per plant, applied to the meristem. (from Hopkins 1995)

Induction of internodal growth in rosette plants by application of gibberellin. Experimental material: White cabbage (Brassica oleracea, var. capitata). The apex of the right-hand plant was treated, from the seedling stage, at regular intervals with GA3 solution; left untreated control. In this case GA induces not only internodal growth but also flower formation, i.e. physiological reactions which also occur during natural bolting of the plants. However, it cannot be deduced automatically that these processes are caused by increased endogenous GA. (after Galston 1961, from Mohr et Schopfer 1995)

The effects of cytokinins on growth and development of cereal plants. (After Kamínek et al. 2003, reprinted from Macháčková et Romanov (eds.): Phytohormones in Plant Biotechnology and Agriculture. Kluwer Academic Publishers, Dordrecht, 2003).

The physiological roles of abscisic acid

stress hormonedormancystomatal closure

The physiological roles of ethylene

acceleration of fruit ripening and other senescence processestriggering of stress reactionsinduction of epinastyinduction of root hairsstimulation of seed germination in certain speciesinhibition of auxin transport

Hypothetical plant hormones

florigenvernalin