Crop Ecophys Auxins

First plant hormone to be discovered

Auxin

Most common ysnthetic auxin

2,4-D

Where is auxin present in all palnts

All parts of the plant although in very different concentrations

Where will there be high auxin production in plants

Where there is active growth

Auxin distribution is achieved through plant by at least 2 physiologically distinct and spatially separated transport pathways:

1) A fast non-polar pathway through the phloem. 2) A slower cell-to-cell polar auxin transport (PAT) pathway mediated through auxin-influx and auxin-efflux carrier proteins.

5 major functions of auxins

1.       Stimulate cell enlargement and elongation

2.       Maintains apical dominance (apical shoot growth dominates that of lateral shoot growth)

3.       Involved in Phototropism (light) and Geotropism (Gravity) responses

4.       Stimulates Root initiation and development

5.       Coordinates fruit growth

Why is growth of lateral buds enhanced in pruning methods?

The basipetal flow of auxin from the apical bud down the stem inhibits the out-growth of the axillary buds on the stem. When the apex of the plant is removed, the inhibitory effect is removed, and the growth of lateral buds is enhanced.

Why are auxins used in some herbicides

At high concentrations, some synthetic auxins are used as herbicides which cause growth disruption and lethal damage to plants by altering auxin-balance. Cause epinasty bending in leaves, a cessation of growth in length, and increased radial expansion. After several days tumors may form, followed by a softening and collapse of the tissue.

— at high concentrations is highly toxic to broad-leaf plants (dicotyledon class of plants). It is commonly used to control broadleaf weeds in monocot grains and grasses. Can use to control weeds in broadleaf crops at lower concentrations but have to be careful with residual effects.

2,4-D

—- another synthetic auxin analog is used for vegetation control on non-crop land because of its high activity and soil persistence

Picloram

Which hormone is used as a fruit thinner, and how?

Auxin, use synthetic auxin to stimulate abscission zone formation during early fruit development to remove excessive numbers of young fruit from apple and pear trees

Using auxins as chemical fruit thinners is a common orchard management practice. WHY?

1)       To increase the total marketable yield by increasing the size of the remaining fruit

2)       Reduce biennial bearing in order to maintain consistent production levels from year to year

Auxins including —- and — applied during the mid-stages of fruit growth can delay or prevent abscission. (Prevent fruit drop)

NAA, 2,4-D

Which hormone used to prevent fruit drop

auxins

How do auxins stimulate root development

by inducing root initials from cells in the stem