On germination a seed first produces shoots with leaves, flowers appear later,
A. Why do you think this happens?
B. How is this advantageous to the plant?
A. As soon as seed germinates, the plant enters into vegetative growth period. This period takes light stimulus (a critical length of light exposed to different plant, i.e., photoperiod) and synthesise the florigen (a flowering hormone) which induce flowering.
B. The vegetative growth period prepares the plant to bear reproductive structures like flower, fruits and seeds, and allows it to grow, mature and reproduce.
Fill in the blanks
A. Maximum growth is observed in ............. phase.
B. Apical dominance is due to ............
C. ........... initiate rooting .
D. Pigment involved in photoperception in flowering plants in ............ .
A. Exponential
B. Auxin
C. Cytokinin
D. Phytochrome.
Some annual food plants such as wheat do not flower, unless they experience a low temperature. They remain vegetative during spring (warm period) but grow further to bear flowers and fruits after receiving low temperature (in winter).
The low temperature in winter prevents precocious reproductive development in autumn, thus enabling the plant to reach vegetative maturity before reproductive phase.
Thus, when spring varieties are planted in spring, they flower and bear fruits prion to end of growing season. But, if the winter varieties are planted in spring, they fail to flower and produce mature grains before the end of growing season, as they could not perceive low temperature of winters.
It is known that some varieties of wheat are sown in autumn but are harvested around next mid summer.
A. What could be the probable reason for this?
B. What term is used for this promotion of lowering under low temperature?
C. Which plant hormone can replace the cold treatment?
A. Annual winter wheat plants take one year full growing season for the completion of their vegetative growth period and then initiate flowers and fruits. This is because after they form seedlings in autumn, they receive low temperature throughout winter, which enables them to reach vegetative maturity. They resume growth in spring and bear flowers and grains towards mid-summer.
B. The chilling or cold treatment of seeds to reduce flowering is called vernalisation. It is a process of shortening of the juvenile or vegetative phase and hastening flowering by a previous cold treatment. This stimulus of vernalisation is perceived only by the meristematic cells. e.g., shoot tip, embryo tip, root apex, developing leaves, etc.
C. GA or gibberellic acid treatment can replace cold treatment and can induce flowering early by reducing vegetative growth period in many long-day plants.
Name a hormone which
A. is gaseous in nature
B. is responsible for phototropism
C. induces femaleness in flowers of cucumber
D. is used for killing weeds (dicots)
E. induces flowering in long day plants.
A. Ethylene is a hormone which is gaseous in nature.
B. Auxin (synthetic auxin 2-4 D) is responsible for phototropism and geotropism in plants.
C. Ethylene causes feminising effect. External supply of very small quantity of ethylene can increase the number of female flowers and hence fruits as in cucumber.
D. Synthetic auxin (2-4 D) kills broad leaved dicot weeds, hence used as weedicides.
E. Gibberellins, induces flowering in long-day plants.