Juvenility and flower bud differentiation

 

Juvenility:

• Juvenility is the period in which a plant cannot produce flowers.
• It occurs in the initial stage of a plant.
• In this stage the development of new parts takes place. It can last up to 20-30 days and can go up to 30-40 years depending upon the type of plant.
• It can be considered as childhood phase of a plant.

BUD:

• A bud is and underdeveloped part of a plant.
• It produces at the tip of the stem.
• A flower is produced from a bud after its maturing.
• It is generally protected by layers of leaves or some gummy substance.

Flower bud differentiation. Definition:

In most fruit trees of the temperate zone, flower buds are fully differentiated before winter, but in olives, differentiation occurs during or at the end of winter. A period of chilling temperatures is needed to proceed irreversibly from flower bud induction to differentiation.

Juvenility is defined strictly in terms of ability of seedlings to form flowers. The juvenile phase ends with the attainment of the ability to flower. The appearance of the first flowers on the seedling is the first evidence that the plant is in the adult phase. Any transition period between the 2 phases is qualitatively the same as the adult phase, but there is presently no method for distinguishing such a transition period from the juvenile phase. The distinction between seedlings in the juvenile phase and young, vegetatively propagated trees, which do not flower, is emphasized. Seedlings which have responded to growth retardant treatments by flowering at an earlier age are considered to have been in a transition period at the time they were treated.

Flower Bud Differentiation

• Development of flower parts following initiation.
• Flower differentiation can take from only a few days in annual plants to 4-11 months in fruit crops.
• Flower induction is the physiological process in the plant by which the shoot apical meristem becomes competent to develop flowers.
• Usually Flower differentiation takes place after flower induction. (with some notable exceptions such as in kiwifruit, where the two processes are separated) Flower induction can be reversed, but flower differentiation is irreversible, because anatomical changes are in place. 
• Methods to shorten juvenility
  • Long-day treatment - shorten the juvenility form 5～10 year to 1 year of bridge Grafting- speed up flowering of fruit crops in 2-3 year.
  • GAs treatments- can induce flowering in juvenility of ivy, cypress and fig.
  Transitional stage Have both juvenile and mature tissue
  • May revert back to juvenile if environmental conditions are right. Involves the transition of a vegetative meristem, producing leaves and stems, into a floral meristem, producing flowers

  Flower Initiation and Development
  a. Irreversible change in which to bud (meristem) changes from growing vegetative tissue to reproductive tissue

  b. Improper conditions can cause flower buds to abort

  1.    High temp 2. Moisture stress

  c. Flowers can be induced naturally or through PGR (plant growth regulators)

  Maturity or reproductive stage

  • Stage where plants are ready to flower.
  • Flowering - ultimate expression of mature state Changes influence by environment. Environment serve as expression changes regulator
  • Changes in physiology and morphology Transformation of primodium of stem, leaf or vegetative part to primodium reproductive organ
  • One way transformation Many plants produce flowers independent of environmental conditions

  Senescens

  The final stage in a plant’s life cycle

  a.     May occur naturally or accelerated by environmental conditions including pathogenic attack

  b.    Cell and tissues deteriorate

  c.     Partial senescence is when plant organs age and eventually die

  d.    Complete senescence is when the whole plant dies. 

  • Monocarpic plant – flowering and fruiting once 
  • Polycarpic plant – many times/repeat.

  Flowering in SDP:

  • Short day plants flower when the night period is long. In day light or red light, phytochrome red (Pr) is converted to phytochrome far red (Pfr).
  • The conversion actually only requires a brief exposure to white or red light.
  • In the dark, Pfr is slowly converted back to Pr.
  • A long night means that there is a long time for the conversion.
  • Under short day conditions (long night) at the end of the night period the concentration of Pfr is low.
  • In SDP, low Pfr concentration is the trigger for flowering.

  Flowering in LDP: 

  •  Long day plants flower when the night period is short.
  • In day light (white or red) the Pr is converted to Pfr.
  • During periods when the day light period is long but critically the dark period is short, Pfr does not have long to breakdown in the dark.
  • Consequently there remains a higher concentration of Pfr.
  • In LDP, high Pfr concentration is the trigger to flowering.