Friday, January 20, 2012

Hormones are flowing!

The first willow catkin of spring! – a wild "pussy willow" –What can cause such a willow flower to spring from a twig appearing dead with winter?

Stream willow - "pussy"... Seen this last week...

Plants like animals can produce hormones – and each plant hormone has dramatic effects on the growth, flowering and fruiting, ripening, and preparation for cold weather in the fall… every step in the growth and development is the plant is influenced by hormones.

Hormones at work

Each plant cell has within it a full copy of the genetic information of the plant, one half from the male parent and one half from the female parent. Most of this genetic information lies dormant most of the time.

Growth bud - source of Auxins! ( fig tree - last season)

When the right stimulus is present a sequence of events is started that results in the activation of the segment of DNA required for the production of a specific hormone. When the hormone has been produced specific changes in the growth of the plant are inevitable as long as the hormone remains present. Then when no longer needed there are natural chemical feedback systems that shut down the gene and its hormone production.

The hormone that stimulates flowering is not currently well understood

The plant does not “decide” “plan” or “think”… these are purely natural sequences of events initiated by certain stimuli:

Hormones control "fruit" formation, seed formation, and ripening ( milk weed "fruit")

So this is the process...Stimulus– activation of genes – production of hormone – hormone effect on plant cells – the emergence of a specific growth pattern. – Mechanism to shut down the gene when no longer needed. – The hormones can control bending toward the light, responding to gravity, sudden rapid growth, bud or root growth, leaf senescence in the autumn… flower and fruit formation and ripening, and much more!

Kiwi fruit: Vine elongation, flowering, seed and fruit formation, senescence in the fall - all controlled by different genes that produce the correct hormone at the right time...

A significant spring time hormone is "Gibberelins", a hormone that brings about the end to winter dormancy. The stimulus in the spring that activates Gibberellines is the length of the night ( period of darkness ). Under its influence many small growing plants ( Like lettuce cabbage, radishes ) suddenly shoot us many inches tall in a few days time - this is called "bolting".

This rapid upward growth is the work of Gibberellins!: Tower of Jewels in our garden last year

Auxin is another powerful hormone. It is produced in the buds of growing plants. Just the right amount will stimulate cell elongation, too much will inhibit growth. When the bud produces auxin, and bright sunlight shines on one side of the bud it will inhibit the auxin on that side- so cells on the darker side will elongate more – causing the stem to bend toward the light. It also is involved in root formation.

The buds, source of auxin is stimulating growth - and even controls the twisting of the tendrils that attach the vine to trees ... Wild cucumber

Have you ever added one ripe banana to a closed sack with several green bananas? The ripe banana is releasing a gas “ethylene” which acts as a hormone to stimulate the other bananas to begin the ripening process. Try it – it works!

Research has generally begun by studying the effects of plant hormones – then working back to learn about the cell changes, the tissue source, and finally to discover the type of hormone. There are still many questions waiting to be solved to fully understand plant hormones. Plant scientists do not fully understand the full process for how some stimulus can activate or turn off a certain gene coding for a hormone.

Hormone patterns appear to be nearly universal - "newly discovered" plants don't usually hold any surprises...

There are chemical pathways that have not been explored. There are even certain plant effects that are probabily caused by a yet unknown hormone… But the basic mechanism of several hormones is understood and this gives hope that additional plant hormones can be found and understood.

Test question: What hormone caused this growth pattern?