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Plant Growth and Movements Summary

Growth is one of the most fundamental characteristics of living organisms. It is accompanied by differentiation. The growth cycle of an annual monocarpic angiosperm begins with the zygote which undergoes a period of dormancy. Later, the dormant embryo develops into a seedling which grows into a vegetative phase and ultimately matures into the reproductive phase. The plant finally enters into the senescence stage which leads to death.

Natural plant growth regulators or phytohormones regulate growth and differentiation. These include auxins, gibberellins, cytokinins, ethylene and ABA. Phytohormones act synergistically or antagonistically. Dormancy is overcome by various kinds of influences.

Most viable seeds require the availability of sufficient quantities of water and oxygen and a suitable temperature for their germination. What is crucial for seed germination is the quality of light to which the seeds are exposed last. The light sensitivity is due to the presence of phytochrome, which exists in 2 interconvertible forms Pr and Pfr. Mangrove plants exhibit vivipary.

Flowering is under the control of daily length of light (photo period) and temperature. Depending upon the photoperiodic responses, 3 categories of plants exist namely SDP, LDP, and day neutral plants.

Flowering is a phytochrome-mediated process. The site of perception of light is the green leaf. Plant physiologists have proposed the existence of a flower inducing growth hormone, the florigen, which has not been isolated. The low temperature requirement for flowering is called vernalisation.

Senescence involves a gradual cessation of functional activity and increased cellular breakdown and metabolic failures. Senescence helps maintain plants efficiency and helps in recycling of materials.

Anchored plants show slow movements of their parts. Growth movements are caused due to differentiation or unequal growth of an organ. Some growth movements are autonomic i.e., self controlled e.g., nutations. Others are paratonic such as light, gravity, water or contact. Paratonic movements are further classified into 2 types:

Tropic movements and nastic movements

Turgor movements occur due to the differences in the turgidity or water potential of the groups of cells in different parts of the plant.

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