Effects of elevated CO2 on growth and photosynthesis with three different cultivars of radish: which is the most limiting for maximal growth, source or sink capacity?

Abstract

Previously we found that radish cultivar of White Cherrish with big storage root did not show down-regulation of photosynthesis and over-accumulation of carbohydrates under elevated CO2 (Plant Cell Physiol 39, 1- '98). The effects of elevated CO2 on growth and photosynthesis were investigated with three different cultivars of radish. Cherry Belle which showed down-regulation of photosynthesis under elevated CO2 (Moore, Bd et al. Plant Cell Environ 21, 905- '98), Kosena with a lower storage root being similar to the wild radish, and White Cherrish were used to evaluate the effect of sink capacity on the acclimation of photosynthesis. Plants were grown for 3 weeks under four different conditions (9hL/15hD or 14.5hL/9.5hD and 35 Pa or 75 Pa CO2). Under elevated CO2 dry weights (DW) increased 1.4 to 2.5 folds. The rate of photosynthesis with the first leaves, under CO2 concentration of 35 Pa, were similar within the cultivars at the exception of Kosena grown under 14.5hL/9.5hD and elevated CO2 which showed lower rate. The DW of Kosena (n=7) under this treatment showed particularly large variations (9.1 to 17.9 g). There was a significant negative correlation between total DW of plant and DW of the first leaf. This result indicates that plants with high sink capacity absorb photosynthate and produce large biomass but plants with lower sink capacity accumulate photosynthate in source leaves and decrease their rate of photosynthesis. Therefore with radish, sink capacity but not source capacity seems to be responsible for maximal growth.