Interaction of cytokinins with UV-B (280 -315nm) on the expansion growth of cucumber cotyledons

Abstract

The negative effect on plant responses are expected due to increased amounts of ultraviolet B UV B radiation reaching on the Earth rsquo s surface by stratospheric ozone depletion Cytokinins CKs are essential phytohormones in plant growth and development Perusal of relevant literature reveals that CKs mitigate the oxidative damage caused by abiotic stresses like salt drought high temperature and heavy metal due to their antioxidant effects However very few reports are available on the interaction of CKs with UV B stress on the expansion growth of the cucumber cotyledons CKs induced the expansion growth of the excised cucumber cotyledons in the darkness CKs induced expansion growth of cucumber cotyledons in darkness was inhibited by supplemental UV B UV B radiation enhanced the level of oxyradicals like superoxide and hydroxide radicals in the excised cucumber cotyledons which was evident by EPR spectroscopy CKs like Zeatin TDZ BAP and FAP reduced the level of oxyradicals produced in the dark grown cucumber cotyledons while promoting the expansion growth of the cotyledons Production of oxyradical in UV B exposed cotyledons showed that these oxyradicals might partially account for inhibition of expansion growth Since considerable amount of oxyradicals were quenched by CKs at higher concentrations and micro g ml it partially restores the inhibition of expansion growth caused by UV B stress It indicates that overproduction of oxyradicals by UV B could not be entirely responsible for the inhibition of CKs induced expansion growth of cotyledons which might be caused by some other physiological changes caused by UV B irradiation in addition to the production of oxyradicals UV B is also known to inactivate protein inhibitor of peroxidase in cucumber cotyledons This may reduce the antioxidants defence and enhance the damaging effects of oxyradicals for the growth of cotyledons