Cytokinins are phytohormones that promote plant growth and development. They stimulate cell division and upregulate expression of photosynthetic-associated genes. However, the main reason for cytokinin research is their anti-senescing action used to delay the onset of plant senescence, improve productivity and postharvest storage. Exogenously applied cytokinins, like 6-benzylaminopurine, are commonly use to slow down or even inhibit the leaf yellowing and prolong lifespan of economically important plants. Similar effects, the regreening of mature fully-developed basal leaves, can be obtained by removal the top of the plant redirecting cytokinins flow from roots back to the ageing structures. Nevertheless, the real breakthrough was the engineering of transgenic tobacco plants with an inserted gene of cytokinins biosynthetic pathway (ipt) fused with a senescence-specific promoter (PSAG12). Enhanced hormones synthesis results in a leaf ageing retardation and its negative auto-regulated activity prevents developmental abnormalities. We studied the capacity of elevated hormone level in the transgenic tobacco to reduce chlorophyll, soluble proteins and Rubisco degradation in plants exposed to nine days of light deprivation. We also investigated possible correlation between the enhanced cytokinin synthesis and antioxidant properties of PSAG12–IPT plants analyzing three isoforms of superoxide dismutase. This paper is an attempt to determine molecular and physiological basis of cytokinin role in an inhibition of leaf ageing.
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