Study on photosynthetic characteristics of Orychophragmus violaceus related to shade-tolerance

Abstract

Orychophragmus violaceus is annual or biennial shade-tolerance, wild ornamental plant. Brassica juncea is shade-intolerance plant. The photosynthetic parameters in the attached leaves of O. violaceus and B. juncea related to shade-tolerance were measured. Light compensation point, CO 2 compensation point, and the carboxylation efficiency in O. violaceus are significantly lower than those in B. juncea. The net CO 2 assimilation rate and the CO 2 terminal concentration of sealed photosynthetic reaction flask of detached leaves of the two species of plants under the weak illumination (34 μmol m −2 s −1) were also determined. The results show that the net CO 2 assimilation rate varies in 1 day with the time when the leaves are detached. The net CO 2 assimilation rate of O. violaceus is much higher than that of B. juncea. The extracellular carbonic anhydrase inhibitor-acetazolamide obviously inhibits the net CO 2 assimilation rate of the two species of plants. The net CO 2 assimilation rate of O. violaceus is positive in 1 day, and there is no obvious photosynthetic midday depression under the weak illumination. The CO 2 terminal concentration of sealed photosynthetic reaction flask of detached leaves of O. violaceus is lower than that of B. juncea. It proves that the CO 2 compensation point of O. violaceus is lower than that of B. juncea, and the net CO 2 assimilation rate is much higher than that of B. juncea under the same illumination duration. Modulating water metabolism relationship by the higher activity carbonic anhydrase is an important shade-tolerance mechanism of O. violaceus.