Carbonic anhydrase in leaves during radish plant ontogeny and glucose effect

Abstract

Radish (Raphanus sativus L.) plants were grown in a greenhouse in soil at natural illumination, temperature, and CO2 concentration. A relationship between the activity of soluble carbonic anhydrase (sCA) and the content of soluble carbohydrates (sCH) was investigated depending on leaf position on the stem during plant development. Indices characterizing leaf ageing during the phase of vegetative growth (PVG) (in lower leaves as compared to upper ones) were a decrease in the rate of photosynthetic release of O2, photosynthetic efficiency, quantum efficiency of photosystem II, and the content of chlorophylls a and b. During PVG and the phase of flower bud formation, the activity of sCA and the contents of sCH, soluble protein, and Glu were the greatest in young (topmost) leaves and declined in the leaves of middle and lower storeys. From the top to the middle leaves, a dependence of sCA activity on the content of Glu or other sCH (without Glu) was direct, whereas, from the middle and the lower leaves, it became inversed. During leaf ageing in vegetatively growing plants and in the phase of budding, the relation between sCA and a relative content of Glu (percent of the rest sCH) was similar to that described above and yielded broken lines, and, during flowering, an inverse relation was observed in the leaves of all three storeys with a low content content of Glu and a low sCA activity. In order to study a dependence of sCA activity on the levels of sCH and Glu during PVG, one half of the leaf was incubated in a thin layer of water at a light schedule: by 12 h of night/day/night + 3-h-long illumination (control material). Within the period of active growth of the hypocotyl up to the storage root formation, the sCA activity and the content of sCH in the leaves incubated in water (control) increased. During a later PVG, both characteristics declined with sCA activity reduced stronger. The rate of the photosynthetic O2 release changed in accordance with the changes in sCA activity. Incubation of the other half of the same leaf in 20 mM Glu during early PVG brought about a considerable increase in sCA activity as compared with control material. During a later PVG and at a much greater Glu concentration (330 mM), its content in the leaves increased manifold; however, there were no significant changes in the activity of sCA, the content of protein or chlorophyll. It was concluded that the activity of sCA in the radish leaves during PVG was not regulated by the absolute content of sCH or Glu in the leaves but depended on endogenous factors associated with plant development.