Tag: plants and animal hormones

Cytokinins are the plant growth hormones that regulate the cell division in root and shoot of the plant both in vivo and in vitro. They do so by regulating the controls that govern the transition of the cell from one stage of the cell cycle to the next one. Thus, option C is correct  

Cytokinins are the growth substances which act primarily on cell division and have little or no effect on extension growth. Cytokinins are derivatives of purine base, adenine, bearing furfuryl substituent. Thus option C is the correct answer. 

Cytokinins have a striking quality to retard senescence (i.e., process of ageing) in plants. External application of cytokinins delay the rate of chlorophyll disappearance and protein degradation which usually accompanies the process of senescence in leaves.

Cytokinins stimulate cell division, even in non-meristematic cells, in presence of auxin. They are most abundant in the growing tissues which are active site of cell division, for example: root, embryos, fruits etc. Cytokinins delay senescence of leaves via their effect on translocation of metabolites and by reducing breakdown of proteins and chlorophyll (the Richmond-Lang effect). Option A is correct. Cytokinins treated leaves withdraw their nutrients from adjacent leaves and maintain their viability. Option C is incorrect as gibberellins (GA) cause cell elongation. Treatment with gibberellins causes bolting (stem elongation) and reverses dwarfism by increasing the intermodal length. Exogenous application of gibberellins prevents senescence in leaves and fruits. Auxin serves as inhibitor of leaf senescence by inhibiting synthesis of abscission layer at the base of petiole or pedicel which in turn causes leaf shedding. Option B is incorrect as auxin is the hormone of cell division and cell expansion both. CoA is a coenzyme which is involved in many metabolic activities like synthesis and oxidation of fatty acid. This makes option D incorrect as CoA is not a plant growth hormone

Cytokinins stimulate cell division, even in non-meristematic cells, in presence of auxin. They are most abundant in the growing tissues which are active site of cell division, for example: root, embryos, fruits etc. This makes option C correct. Option A is incorrect as auxins are the growth hormones that cause cell division as well as cell expansion, thereby causing growth while cytokinins are not involved in cell expansion but only in cell division. Option B is incorrect as gibberellins cause cell elongation. Treatment with gibberellins causes bolting (stem elongation) and reverses dwarfism by increasing the intermodal length. Trypsin is a globular protein with 24kD and one polypeptide chain of 220 residues and serves as proteolytic enzyme (protein digesting enzyme). Option D is incorrect. 

Option D is incorrect as IAA is an auxin that causes apical dominance. It involves withdrawal of root manufactured cytokinins towards apical bud which in turn makes the lateral bud cytokinins deficient. Cytokinins deficiency suppresses growth of lateral buds as cytokinins are the hormones of cell division. Pruning is cutting off the apical portion of branches to induce growth which in turn lowers the amount of auxin synthesized as shoot apex. The lowered auxin synthesis allows translocation of cytokinins to lateral bud stimulating cell division and growth of lateral branches. This makes option C correct. Option A is incorrect as ethylene inhibits lateral buds and causes apical dominance. Option B is incorrect as gibberellins are the hormones of stem elongation of genetic dwarfs and seed germination. 

The cytokinins are plant growth substances which act primarily on cell division and little or no effect on extension growth. The most important function of cytokinins is the promotion of cell division. It is now well established that these are true cell division factors. The varying amount of cytokinins, along with sufficient auxin is required for the growth of callus in the tissue culture experiments. Thus option B is the correct answer.

Cytokinin promotes cell division and cell elongation. Thus they are found in the region where there is rapid cell division like fruits and seeds.

Cytokinins are a class of plant growth substances that promote cell division, or cytokinesis, in plant roots and shoots. They are derivatives of pure adenine. It is a true cell division factor, promotes meristematic tissue regions. It prevents destruction of chlorophyll in leaves.

Cytokinins retard the aging in plants. The effect is called as Richmond-Lang effect. Richmond-Lang effect is retardation of aging due to cytokinins which acts by retarding the rate of destruction of chlorophyll and yellowing of leaves.