Growth and Development of Horticultural Crops (1+1)

Physiological effects of kinetin (Cytokinins)

1. Cell division

• One of the important biological effects of kinetin on plants is to induce cell division in the presence of sufficient amount of auxin (IAA), especially in tobacco pith callus, carrot root tissue, soybean cotyledon, pea callus etc.,
2. Cell enlargement

• Like auxins and gibberellins, the kinetin may also induce cell enlargement.
  
• Significant Cell enlargement has been observed in kinetin treatment in leaf discs cut from etiolated leaves of Phaseolus vulgaris, pumpkin cotyledons, tobacco pith cultures, cortical cells of tobacco roots excised Jerusalem artichoke tissue etc.,
3.Initiation of inter-fascicular cambium

• Kinetin can induce formation of inter - fascicular cambium. This has in fact been shown by Sorokin et al. (1962) in pea stem sections.
4. Morphogenesis

• Kinetin also has ability to cause morphogenetic changes in an otherwise undifferentiated callus.
  
• For instance the tobacco pith callus can be made to develop either buds or roots by changing the concentration of kinetin and auxin.
5. Counteraction of apical dominance

• Cytokinins play a role in initiating the growth of lateral buds has also been proved by physiological studies made on cytokinin overproducing mutants of tobacco.
6. Dormancy of seeds

• Like gibberellins, the dormancy of certain light sensitive seeds such as lettuce and tobacco can also be broken by kinetin treatment in dark.
  
• The inhibitory effect of far-red light treatment on the germination of the above seeds is also overcome by kinetin treatment.
7. Delay of senescence: The Richmond –Lang Effect

• The ageing process of the leaves usually accompanies with loss of chlorophyll and rapid breakdown of proteins.
  
• This is called senescence. Richmond and Lang showed that this senescence could be postponed to several days in detached Xanthium leaves by kinetin treatment.
• This effect of kinetin in delaying the senescence is called as Richmond-Lang effect.
  
• One of the important factors in delay of senescence in kinetin treated leaves is their physiological age.
  
• Mature leaves of Nicotiana rustica have been found to be more responsive to kinetin treatment in delaying senescence than the younger leaves.
8. Promotion of chloroplast development

• Cytokinins are known to enhance conversion of etioplasts into chloroplast when etiolated seedlings after treatment with cytokinins are exposed to light.
  
• In such cases, the chloroplasts develop extensive grana and chlorophylls and the rate of synthesis of photosynthetic enzymes is much greater in comparison to those etiolated seedlings which are illuminated without cytokinin treatment.