• Auxins are produced at the apex of the shoot (apical meristem). The main auxin is indoloaceteic acid (IAA) produced from the amino acid
tryptophan. It is transported back down the shoot to the zones of elongation in roots and shoots where it regulates cell extension and
elongation and the differentiation of vascular tissues. The auxin IAA inhibits lateral buds from growing into side shoots and this is called apical
dominance. Leaf expansion and the growth of fruits and seeds are also controlled by the IAA auxin. The discovery of auxins resulted from
investigations into why plants tended to grow towards a source of light. Light on a shoot causes more auxin to be released on the shaded side. The
result is the shaded side elongates more and the shoot bends towards the light. It has been suggested that auxins enable the cell walls to be
stretched more easily by the osmotic forces in the vacuoles.
• Cytokinins are frequently found in xylem sap. They are thought to be synthesised in the roots and are carried to other parts of the plant in the
transpiration stream. Their production is highest when a plant is growing rapidly as they promote cell division and then production falls off as
ageing begins.
• Gibberellins take their name from a fungal parasite Gibberella fujikuroi which causes disease in rice plants. Seedlings which are attacked by the
fungus develop very long internodes so the shoots are much taller than healthy plants. The growth promoting substance was gibberellic acid.
Many similar substances to gibberellic acid have been isolated from higher plants. They are made at the tips of roots and shoots. While
the best known effect of gibberellic acid is internode elongation it also stimulates enzyme production during seed germination and plays a role in cell
division and tissue differentiation. In spite of the many different specific gibberellins found in plants, most are inactive forms that serve as
biosynthesis precursors or breakdown products of the active gibberellic acids.
·
Daylight contains move red than far red light, P660 is converted to P730 during
the day. As day length gets longe the P730 increases. In LDP's as day length
increases, the amount of P730 reaches a critical level that initiates flowering.
The intensity of light is important as conversion is quicker in high light
intensities. The P730 form is the physiologically active form, whether it is
Plants contain growth promoters and inhibitors
Coordination and Control that sufficient P730 has accumulated to promote flowering in LDP's or that
which control plant growth and development. in plants there is too much P730 to allow flowering to occur in SDP's . The inhibitory
effect of high levels of P730 must be removed before flowering can take place.
Phytochrome is a pigment system in leaves of Phytochrome pigments act as a photoreceptor it is sensitive
flowering plants. Some species have flowering to light and exists in 2 forms: Red light (660nm) Stimulatory
initiated by temperatures reaching a certain
temperature, but most are triggered by duration
• P660 absorbs red light with an absorption peak of
660nm P660 P730 or
inhibitory
• P 730 absorbs far red light with an absorption peak at Far red light (730nm)
is
of light or day length (photoperiod). effect.
730nm
If subjected to red light the P660 is rapidly converted to the
P730 and if the P730 is subjected to far red light it is rapidly
converted to P660. In darkness, P730 will slowly convert to the
LDP's - long day plants which SDP's - short day plants which P660 form, as it is much less stable. Slow conversion in
flower only if the day length only flower if days are charter darkness
exceeds a minimum length than a critical value.
Short day - P660 is converted to P730 during the day. The Short day - P660 converts to P730 during the day, the long In short day plants - the critical period of darkness must be continuous
long night dark period is long enough of a sufficient Iong night night is enough for sufficient P730 to be slowly as a short flash of light will rapidly convert to P660 to P730, whereas the
Flowering level of P730 to be converted to P660 to converted back to P660 to prevent the P730 conversion of P730 to P660 is slow.
remove the inhibitory effect of P730. No flowering
reaching the critical level needed for flowering.
Long day - P660 is converted to P730 during the day Long day - Long day length allows P660 to be converted to
short night but the dark period is not long enough for short night P730 in high concentrations, the darkness is too
No flowering a sufficient level of P730 to be converted to short for enough P730 to be converted to P660.
Flowering
P660 to remove the inhibitory effect of P730 builds up to critical level.
P730.
tryptophan. It is transported back down the shoot to the zones of elongation in roots and shoots where it regulates cell extension and
elongation and the differentiation of vascular tissues. The auxin IAA inhibits lateral buds from growing into side shoots and this is called apical
dominance. Leaf expansion and the growth of fruits and seeds are also controlled by the IAA auxin. The discovery of auxins resulted from
investigations into why plants tended to grow towards a source of light. Light on a shoot causes more auxin to be released on the shaded side. The
result is the shaded side elongates more and the shoot bends towards the light. It has been suggested that auxins enable the cell walls to be
stretched more easily by the osmotic forces in the vacuoles.
• Cytokinins are frequently found in xylem sap. They are thought to be synthesised in the roots and are carried to other parts of the plant in the
transpiration stream. Their production is highest when a plant is growing rapidly as they promote cell division and then production falls off as
ageing begins.
• Gibberellins take their name from a fungal parasite Gibberella fujikuroi which causes disease in rice plants. Seedlings which are attacked by the
fungus develop very long internodes so the shoots are much taller than healthy plants. The growth promoting substance was gibberellic acid.
Many similar substances to gibberellic acid have been isolated from higher plants. They are made at the tips of roots and shoots. While
the best known effect of gibberellic acid is internode elongation it also stimulates enzyme production during seed germination and plays a role in cell
division and tissue differentiation. In spite of the many different specific gibberellins found in plants, most are inactive forms that serve as
biosynthesis precursors or breakdown products of the active gibberellic acids.
·
Daylight contains move red than far red light, P660 is converted to P730 during
the day. As day length gets longe the P730 increases. In LDP's as day length
increases, the amount of P730 reaches a critical level that initiates flowering.
The intensity of light is important as conversion is quicker in high light
intensities. The P730 form is the physiologically active form, whether it is
Plants contain growth promoters and inhibitors
Coordination and Control that sufficient P730 has accumulated to promote flowering in LDP's or that
which control plant growth and development. in plants there is too much P730 to allow flowering to occur in SDP's . The inhibitory
effect of high levels of P730 must be removed before flowering can take place.
Phytochrome is a pigment system in leaves of Phytochrome pigments act as a photoreceptor it is sensitive
flowering plants. Some species have flowering to light and exists in 2 forms: Red light (660nm) Stimulatory
initiated by temperatures reaching a certain
temperature, but most are triggered by duration
• P660 absorbs red light with an absorption peak of
660nm P660 P730 or
inhibitory
• P 730 absorbs far red light with an absorption peak at Far red light (730nm)
is
of light or day length (photoperiod). effect.
730nm
If subjected to red light the P660 is rapidly converted to the
P730 and if the P730 is subjected to far red light it is rapidly
converted to P660. In darkness, P730 will slowly convert to the
LDP's - long day plants which SDP's - short day plants which P660 form, as it is much less stable. Slow conversion in
flower only if the day length only flower if days are charter darkness
exceeds a minimum length than a critical value.
Short day - P660 is converted to P730 during the day. The Short day - P660 converts to P730 during the day, the long In short day plants - the critical period of darkness must be continuous
long night dark period is long enough of a sufficient Iong night night is enough for sufficient P730 to be slowly as a short flash of light will rapidly convert to P660 to P730, whereas the
Flowering level of P730 to be converted to P660 to converted back to P660 to prevent the P730 conversion of P730 to P660 is slow.
remove the inhibitory effect of P730. No flowering
reaching the critical level needed for flowering.
Long day - P660 is converted to P730 during the day Long day - Long day length allows P660 to be converted to
short night but the dark period is not long enough for short night P730 in high concentrations, the darkness is too
No flowering a sufficient level of P730 to be converted to short for enough P730 to be converted to P660.
Flowering
P660 to remove the inhibitory effect of P730 builds up to critical level.
P730.
