Coordination and Control in Plants Flashcards
what is the pigment called that is found in the leaves of flowering plants? and what is its job?
-phytochrome is the pigment system
-it is involved in the timing of flowering in plants
how is the flowering process initiated? what triggers it?
-when average temps reach a certain level
-most common trigger is the duration of light or day length
what is another term to describe the duration of day light?
-photoperiod
what are the two species/ types of plants that are controlled by light?
-long day plants
-short day plants
when do long day plants flower?
-when day length exceeds a certain minimum length
when do short day plants flower?
-when day lengths are shorter/ dark period is longer
what is the term used to describe how the photochrome pigment responds to light?
-acts as a photoreceptor
what is the two forms that phytochrome can be found?
-P660
-P730
what type of light does P660 absorb and what is its absorption peak?
-red light with a peak of 660nm
what type of light does P730 absorb and what is its absorption peak?
-far red light with a peak of 730nm
what happens if the plant is subjected to red light in-terms of the pigment conversions? what about far red light?
-the P660 is rapidly converted to the P730 form
-if there is far red light P730 is rapidly converted to the P660 form
in darkness which pigment is more stable and what does this result in?
-P730 is much less stable in darkness than P660
-P730 will therefore convert to the P660 form slowly
what type of light does daylight contain more of and what is the effect of this in-terms of the pigments?
-more red than far red light
-meaning P660 is converted to P730 so as day length/ light gets longer the amount of photochrome in the form P730 increases
what is the effect of a longer day length in flowering in LDPs?
-as day length increases the amount of P730 increases too until it reaches a critical level which then initiates flowering
what happens are day length increases in short day plants and why is this?
-the inhibitory effect of high levels of P730 must be removed before flowering can take place
-this is due to P730 being physiologically active
what is the phytochrome response in LDP when there is a short day and a long night?
-P660 converted to P730 rapidly in the day
-the night/ dark is long enough for sufficient P730 to be converted back into P660
-this prevents P730 reaching critical level and so prevents flowering
what is the phytochrome response in LDP when there is a long day and a short night?
-long day means P660 can rapidly convert to P730
-dark period is not long enough for P730 to convert back to P660
-P730 stays at critical level and so the plant flowers
what is the phytochrome response in SDP when there is a short day and a long night?
-P660 converted to P730 in the day
-dark period is long enough for a sufficient level of P730 to be converted back to P660
-this removes inhibitory effect of high amounts of P730
-the plant flowers
what is the phytochrome response in SDP when there is a long day and a short night?
-P660 converted to P730 during the day
-dark period is not long enough for a sufficient level of P730 to be converted back into P660
-high amounts of P730 results in flowering being inhibited
what is done by flower suppliers to ensure that flowers are available during the whole year?
-the photoperiod is manipulated
what are the two ways that the photoperiod can be manipulated?
-using artificial light
-using screens to reduce the light period
what is the effect of the light and the dark period in LDPs being the same length?
-the length of day is not long enough to build up a supply of P730 to initiate flowering
what is the effect of having a longer light period and a shorter dark period in LDPs?
-flowering is initiated as the light period is long enough for sufficient amount of P730 to reach the critical level
-the dark period is not long enough to break down a sufficient amount of the P730
what is the effect of light period being longer than dark period but the light period is interrupted by a short period of darkness?
-the short amount of darkness does not reduce the amount of P730 level enough so that it falls below the critical level and inhibits flowering
-this is because the conversion of P730 to P660 in darkness is a slow process
what is the effect of having light and dark period the same in a SDP?
-darkness is long enough to allow enough P730 to be converted back into P660
-removes the inhibitory effects of P730
what is the effect of having light and dark period the same in a SDP but the dark period is interrupted by a short flash of light?
-the short flash of light is enough to inhibit flowering as the P660 will be rapidly converted to P730
-therefore there is not a sufficiently long continuous period of darkness to allow for flowering
in SDP what must the period of darkness be to ensure flowering?
-continuous
why do some scientists believe that a hormone is involved in flowering?
-there must be some form of communication between where the light stimulates the phytochrome and where flowering actually occurs
there have been no plant hormones identified but what has been found in plants?
-plant growth substances
what is different about growth in plants compared to animals?
-growth in plants is localised in specific zones at the tips of roots and shoots called apical meristems
what occurs in the meristems of plants/ regions of localised growth?
-mitosis takes place to produce more cells
how else can plant growth occur besides mitosis of cells in the roots? what does this mean that the two zones are in roots and shoots?
-cell elongation
-zones of division and zones of elongation
where else might growth occur in certain plants beside the roots, shoots and tips?
-the internodal regions
-these are parts of the stem between points that leaves develop
what are the three main plant growth substances?
-auxins
-cytokines
-gibberellins
where is the site of production and the main function of auxins?
-produced in the tip and moves down the stem (decreases concentration)
-promotes cell elongation
where is the site of production and the main function of cytokinins?
-produced in the meristem tissues (zones of division)
-promote cell division in internodes
where is the site of production and the main function of gibberellins?
-produced in leaves
-promotes cell elongation
