Plant Growth Regulators, Buds and Bud Initiation

Plant Growth Regulators, Buds and Bud Initiation Describe grapevine vegetative morphology and its function Range: buds, leaves, shoots, tendrils, permanent wood Identify and describe factors affecting grapevine phenology Range: environmental factors, hormones tcreagh@eit.ac.nz

Plant growth Regulators • Hormones are substances synthesized by the plant to act as messengers • They are produced at one site and generally transported in the xylem or phloem to another to induce a physiological reaction (eg growth) tcreagh@eit.ac.nz

Plant growth Regulators • They may also cause different effects in different parts of the grape vine • These reactions are complex and not always fully understood • Very small amounts of hormone are required to cause an action • They may act either alone or interact with other hormones tcreagh@eit.ac.nz

Plant growth Regulators • There are five main groups of hormones in plants tcreagh@eit.ac.nz

Auxins tcreagh@eit.ac.nz

Auxins Source of production • New vegetative growth • Young leaves • Seeds tcreagh@eit.ac.nz

Auxins Actions • Attracts sugar and nutrients to site of production • Stimulates cell growth in young tissue • Inhibits lateral budburst further down the shoot ie apical dominance • Promotes growth towards light tcreagh@eit.ac.nz

Gibberellins tcreagh@eit.ac.nz

Gibberellins Source of production • Young growing shoot and leaves • Root tips Actions • Suppresses flower bud initiation and fruitfulness in cool weather/poor light • Promotes growth and cell elongation Example • GA-3 is sprayed on seedless grapes to increase grape size and yield tcreagh@eit.ac.nz

Cytokinins tcreagh@eit.ac.nz

Cytokinins Source of production • Root tips Actions • Promotes cell multiplication in differentiating tissues at apices • Attracts auxin and gibberellin, sugars, nutrients • Promotes even budburst • Promotes lateral branching tcreagh@eit.ac.nz

Cytokinins • Promotes development of leaves, fruit structures, fruit set with gibberellins to balance fruitfulness of lateral buds • Delays senescence • Promotes berry as a sink • Involved in anthocyanin and flavour formation tcreagh@eit.ac.nz

Abscissic Acid tcreagh@eit.ac.nz

Abscissic Acid Source of production • Mature leaves • Seeds, roots tcreagh@eit.ac.nz

Abscissic Acid Action • Generally counteracts effects of auxin, gibberellin and cytokinin • Induces stomatal closure in response to water stress • Reduces growth in response to water stress, cold and short days • Possibly promotes ripening as auxin production reduces in seeds tcreagh@eit.ac.nz

Ethylene tcreagh@eit.ac.nz

Ethylene Source of production • Mature leaves and other parts of vine Action • Affects many types of growth, not all of which are clearly defined • Promotes ripening and berry colour • Promotes abscission zone development tcreagh@eit.ac.nz

Plant growth Regulators • In general terms, auxins and gibberillins complement each other, promoting growth • Cytokinin induces fruit and ripening when weather conditions and other factors are suitable for fruit to ripen • Absissic acid and ethylene promotes ripening and prepares the vine for dormancy tcreagh@eit.ac.nz

Increase Result Auxin Low light, temperature. Acts with gibberellins to promote growth. Gibberellins Increased by low light, low temperature. Elongates cells producing spindly shoots. Cytokinin Increased by increased light, leaf exposure, warm root environment. Promotes growth and fruit ripening. Absissic acid Increased by lack of water, cool weather, short days. Promotes fruit ripening as fruit becomes a major sink if abscissic acid is greater than auxin. Ethylene Increased by short days, drought, nitrogen deficiency. Artificial application. Physical contact, mechanical damage. Promotes abscission. Improve colour, reduce shoot growth. Reduced shoot growth, enhanced ripening. tcreagh@eit.ac.nz

Some Practical Implications of Hormone Actions 1 • Auxin is produced in the growing tips and travels downwards • To prevent uneven budburst and end point principle, where the end bud bursts first, canes are arched during pruning to slow the movement of auxin along the cane • Spur pruning is not subject to uneven budburst tcreagh@eit.ac.nz

Some Practical Implications of Hormone Actions 2 • Removal of the growing tip will promote lateral growth, as the site of auxin inhibition of budburst is removed tcreagh@eit.ac.nz

Some Practical Implications of Hormone Actions 3 • Shaded shoots tend to grow long and spindly with long internodes until they reach light, where growth becomes normal • Buds also tend to be less fruitful in shaded vines, due to the actions of gibberellin tcreagh@eit.ac.nz

Some Practical Implications of Hormone Actions 4 • Berry size is related to the number of seeds (developed embryos) due partly to hormone production, increasing the berry as a sink tcreagh@eit.ac.nz

Some Practical Implications of Hormone Actions 5 • Warm, well drained soils during budbreak improve the evenness of budburst due in part to cytokinins produced from increased root growth promoted due to the warmer conditions tcreagh@eit.ac.nz

Some Practical Implications of Hormone Actions 6 • Fruitfulness • The number of clusters is increased with warmer temperatures due to cytokinin production • Whereas in shaded or cool situations gibberellins tends to promote tendril formation tcreagh@eit.ac.nz

Some Practical Implications of Hormone Actions 7 • As vegetative growth slows close to ripening, less auxin and gibberellins are produced • Less auxin is produced as the seed ripens in stage 2 tcreagh@eit.ac.nz

Some Practical Implications of Hormone Actions • Abscissic acid increases in proportion inducing veraison and the berry becomes a major sink tcreagh@eit.ac.nz

Some Practical Implications of Hormone Actions • Cytokinin also increases, attracting sugar to the berry, abscissic acid and perhaps having an effect on berry colour and flavour • Continuing ripening during cool climates may depend partially on warmer soil temperatures favouring cytokinin production tcreagh@eit.ac.nz

Hormones and Initiation of Inflorescence Primordia • Hormones are synthesized within the vine control the initiation and development of inflorescence primordia within the bud • They do not act in isolation • Relative proportions of determine what is formed tcreagh@eit.ac.nz

Hormones and Initiation of Inflorescence Primordia • The number size of inflorescences is the first indication of yield tcreagh@eit.ac.nz

Yield components tcreagh@eit.ac.nz

Definitions • Fecundity • the potential reproductive capacity of an organism or population • Fruitfulness • The presence of inflorescence primordia in latent buds • Mean bunch number per shoot • Three step process: • Formation of an uncommitted primordium • Development into inflorescence primordium • Formation of flowers tcreagh@eit.ac.nz

Buds tcreagh@eit.ac.nz

Buds • The grapevine buds develop in the axil of the leaf and the shoot, that is, at the node. • There are various types of grapevine buds: • Prompt bud • Compound bud • Latent bud tcreagh@eit.ac.nz

tcreagh@eit.ac.nz

Lateral or Prompt bud • The lateral shoot arises from the lateral or prompt bud • It is formed between the primary or new season’s shoot and the leaf arising from it, that is, in the leaf axil • It may be also referred to as the true axillary bud tcreagh@eit.ac.nz

Lateral or Prompt bud • The prompt bud can burst in the current season to produce short shoot known as the lateral • However, lateral shoots will form only under certain conditions • Vigorous vines or if topping occurs early in the season tcreagh@eit.ac.nz

Lateral or Prompt bud • Lateral shoots are generally unfruitful but bunches may grow on the lateral shoot • If they do they are usually small and ripen after those carried on the primary shoot • These bunches are referred to as 'second set' tcreagh@eit.ac.nz

Compound Buds • The compound bud is formed after the prompt bud and develops more slowly • These buds also develop in the leaf axil at the node. • It consists of three true buds tcreagh@eit.ac.nz

Compound Buds • The compound bud does not burst until the season after its development • Generally only the middle, or primary, bud bursts to develop the primary (main) shoot • If this is damaged (wind, frost, etc) then the secondary or tertiary buds may burst • However, these buds are generally less fruitful, that is they have fewer bunches per shoot tcreagh@eit.ac.nz

Compound Buds • The number of potential bunches per bud, and therefore per shoot, are determined as the compound bud develops, that is, in the previous season before bud burst. • Note that as the shoot develops, compound buds are developing with the shoot development. • Those at the base of the shoot will be more developed than those close to the apical tip. tcreagh@eit.ac.nz

Compound Buds • Environmental factors during bud development influence the potential crop in 18 months time • A major influence is light interception at the bud and the temperature; increased light and temperature has been shown to result in greater fruitfulness. tcreagh@eit.ac.nz

Latent bud • These are buds that may be any type of bud that do not burst in the season that they are formed • Instead they remain dormant and viable and at some later stage may burst. Latent buds may take several seasons to burst, often as a result of vine damage or heavy pruning tcreagh@eit.ac.nz

Compound bud Lateral scar Leaf scar Compound bud tcreagh@eit.ac.nz

Bud Initiation • Buds undergo differentiation • That is, primordial structures within the bud change depending on plant growth regulators that these structures receive • The level of plant growth regulators that the bud receives is dependant on climatic conditions during differentiation tcreagh@eit.ac.nz

Bud Initiation • Differentiation coincides with flowering • And the slowing down of vegetative growth • Very sensitive to water stress tcreagh@eit.ac.nz

Plant Growth Regulators, Buds and Bud Initiation