Sunday, 3 March 2013

9.3.6 Phytochrome and the control of Flowering

Flowering Cues: 
Plants have to coordinate the production of flowers to coincide with the best reproductive opportunity . There are many environmental cues that affect flowering however the photoperiod isthe most reliable indicator on time of the year.

The photoperiod is the period of day light in relation to dark. In northernly and southern regions, this photoperiod is a reliable indication of the time of year and therefore one of the most reliable indicators of the seasonal changes.

Short and Long day Plants:
Short day plants (SDP) typically flower in the spring or autumn when the length of day is short.
Long day plants (LDP) typically flower during the summer months of longer photoperiod.

Critical Night Length:
Experiments have shown that the important factor determining flowering is the length of night rather than the length of day.
Therefore, SDP have a critical long night and LDP will have a critical short night.

Phytochrome System:
The receptor of photoperiod is located within the lead but the cellular location of the receptor remains unclear. The chemical nature of the receptor is the molecule Phytochrome and phytochrome can be converted from one form to another by different types of light

9.3.3 Dicotyledonous Seed Structure and Function

Testa protects the plant embryo and the cotyledon food stores

Radicle is the embryonic root

Plumule is the embryonic stem

Cotyledonous is the food store for the seed.

Micropyle is a hole in the testa through which the water can enter  the seed prior to germination

Scar is where the ovule was attached to the carpel wall


9.3.2 Pollination and Fertilisation

Pollination refers to the transfer of pollen grains from the anther to the stigma

Fertilisation refers to the fusion of the male gamete nuclei with the female gamete to form a zygote. Pollen grains often contain an additional nuclei used in the fertilisation of the food store cells.

The Seed are the fertilised ovules. The seeds are moved away from the parental plant before germination to reduce competition for limited resources with parental plant. There are a variety of seed dispersal mechanisms including fruits, winds, water and animals.


9.3.1 Structure of an animal-pollinated dicotyledonous Plant

  • Sepals cover the flower structure while the flower is developing and in some species these are modified to petals
  • Petals surround the male and female flower parts and its function is to attract animal pollinators.
  • Stigma is the surface on which pollen lands and the pollen tube grows down to the ovary.
  • Style connects the stigma to the ovary.
  • Ovary contains the ovules of the plant.
  • Filament supports the anther that contain the pollen and together they are called the stamen.