Download factors affecting growth of plant tissue

FACTORS AFFECTING GROWTH OF PLANT TISSUE
The process of initiation and development of an organ is called organogenesis. In plant tissue culture,
inducing organogenesis is an important way to regenerate plants from the culture.
The following points highlight the thirteen factors influencing organogenesis in plant tissue culture.
The thirteen factors are:
(1) Size of Explant
(2) Source of Explant
(3) Age of the Explant
(4) Seasonal Variation
(5) Oxygen Gradient
(6) Quality and Intensity of Light
(7) Temperature
(8) Plant Hormones
(9) Culture Medium
(10) Agar-Agar
(11) pH of the Medium
(12) Ploidy Level and
(13) Age of Culture.
Factor # 1. Size of Explant:
Organogenesis is generally dependent upon the size of the explant. The large explant consisting of
parenchyma, vascular tissue and cambium have greater regenerative ability than the smaller explant.
Factor # 2. Source of Explant:
The source of explant cultured is important in determining the potential of organogenesis. The most
suitable part of the plant for starting culture will depend on the species.
Factor # 3. Age of the Explant:
Leaf explants that are collected from young leaves produce only root, whereas older leaf initiates only
shoot buds and leaves of medium age produce both shoots and roots.
Factor # 4. Seasonal Variation:
The effect of seasonal variation on plant is another factor which exercises an influence on organ
formation. Whether the explant will regenerate invitro depends on the season when it is taken.
Factor # 5. Oxygen Gradient:
In some cultures, shoot bud formation takes place when the gradient of available oxygen inside the
culture vessel is reduced. But rooting requires a high oxygen gradient.
Factor # 6. Quality and Intensity of Light:
Studies on spectral light on organogenesis reveals that the blue region of the spectrum promotes shoot
formation and red light induces rooting.
Factor # 7. Temperature:
Most tissue cultures are grown successfully at temperatures around 25° C, but the usual environmental
temperatures of the species concerned should be taken into account.
Factor # 8. Plant Hormones:
Of the many factors that influence Organogenesis in vitro, the most important single factor seems to be
the phytohormones.
Factor # 9. Culture Medium:
The essential components of plant cell culture medium are the major salts or minor salts. Besides these,
vitamins, amino-acids, carbohydrates etc. are also required for in vitro growth and development of plant
cells.
Factor # 10. Agar-Agar
With high concentration of agar, the nutrient medium become hard and does not allow the diffusion of
nutrient to the growing tissue. So the concentration of agar also plays a role in organogenesis.
Factor # 11. pH of the Medium:
The pH of the culture medium is generally adjusted between 5.6 to 5.8 before sterilization. The pH is
another factor that may have a determining role in organogenesis.
Factor # 12. Ploidy Level:
It is generally observed that with the increase of chromosome instability there is a gradual decline in
morphogenetic potentiality of the callus tissue. So the most important factor in maintaining organogenic potential of the callus tissue is the maintenance of chromosome stability.
Factor # 13. Age of Culture:
A young culture frequently produces organs. But the organogenic potential may decrease and ultimately
disappear in old culture.
MORPHOGENESIS
Morphogenesis is the biological process that causes an organism to develop its shape.
The process controls the organized spatial distribution of cells during the embryonic development of an
organism. Morphogenesis can take place also in a mature organism, in cell culture or inside tumor cell
masses.
Morphogenetic responses may be induced in organisms by hormones, by environmental chemicals
ranging from substances produced by other organisms to toxic chemicals or radionuclides released as
pollutants, and other plants, or by mechanical stresses induced by spatial patterning of the cells.
Molecular basis
Several types of molecules are important in morphogenesis. Morphogens are soluble molecules that can
diffuse and carry signals that control cell differentiation via concentration gradients. Morphogens
typically act through binding to specific protein receptors. An important class of molecules involved in
morphogenesis are transcription factor proteins that determine the fate of cells by interacting with
DNA.
Cellular basis
Morphogenesis arises because of changes in the cellular structure or how cells interact in tissues. These
changes can result in tissue elongation, thinning, folding or separation of one tissue into distinct layers.