A Transient Stimulation of Net Photosynthesis of Rye Leaves by α-Hydroxy-2-pyridinemethanesulphonic Acid (α-HPMS) due to Inhibition of Photorespiratory CO2Release

Abstract

Loboda, T., Kleczkowski, L. A., Tarlowski, J. and Nalborczyk, E. 1988. A transient stimulation of net photosynthesis of rye leaves by a-hydroxy-2-pyridinemethanesulphonic acid (a-HPMS) due to inhibition of photorespiratory C02 release.—J. exp. Bot. 39: 1765-1770. The effects of a-hydroxy-2-pyridinemethanesulphonic acid (a-HPMS) upon net photosynthesis (Pn), the CO2 compensation point (/'), post-lower illumination burst of C02 (PLIB) and post-lower temperature burst of C02 (PLTB) in detached rye (Secale cereale L.) leaves were investigated. At low concentrations (< 05 mol m~3), a-HPMS initially stimulated P„ and decreased the magnitude of both PLIB and PLTB. The T decreased at all concentrations of a-HPMS (005-5 0 mol m~3). The effects of a-HPMS on P„ and F were time-dependent and, after a few minutes, the P„ was inhibited while r values increased considerably. At a higher concentration (5 0 mol m 3), the transient effects of a-HPMS were shorter \F) or not observed at all (P„). Both PLIB and PLTB, when expressed in relation to P„, increased at higher levels of this compound. Similar data with respect to the effects of a-HPMS on PLIB and PLTB were found for leaves of dandelion (Taraxacum officinale L.). The results suggest that a-HPMS may stimulate P„ by inhibiting photorespiration, as originally suggested by Zelitch ( 1966), but only at low concentrations and over a short time span. The decrease of PLIB and PLTB values at low a-HPMS levels is consistent with these processes being a residual activity of the glycolate pathway.