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

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, CO2 compensation point, and the carboxylation efficiency in O. violaceus are significantly lower than those in B. juncea. The net CO2 assimilation rate and the CO2 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 CO2 assimilation rate varies in 1 day with the time when the leaves are detached. The net CO2 assimilation rate of O. violaceus is much higher than that of B. juncea. The extracellular carbonic anhydrase inhibitor-acetazolamide obviously inhibits the net CO2 assimilation rate of the two species of plants. The net CO2 assimilation rate of O. violaceus is positive in 1 day, and there is no obvious photosynthetic midday depression under the weak illumination. The CO2 terminal concentration of sealed photosynthetic reaction flask of detached leaves of O. violaceus is lower than that of B. juncea. It proves that the CO2 compensation point of O. violaceus is lower than that of B. juncea, and the net CO2 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.