The effect of light intensity on the growth rate of wild-type and <i>tla3</i> mutant <i>Chlamydomonas reinhardtii</i>

Abstract

The TLA3 gene in Chlamydomonas reinhardtii encodes the chloroplast signal recognition particle protein CpSRP43, which has a role in coordinating signal recognition events in the chloroplast during photosynthesis (Kirst et al. 2012, Gao et al. 2015). This study examined the effect of light intensity and the effect of a deletion in the TLA3 gene, which resulted in the truncated light-harvesting antenna3, on the growth rate of the organism. We incubated both the wild type and the tla3 mutant under three light intensities of 1200 lux, 3000 lux, and 10000 lux at a constant temperature of 17˚C for a total of 14 days. We counted the cells 8.92, 11.96, and 13.96 days of incubation, plotted the counts using exponential equations, and obtained the growth rates from the slopes. We then used the two-way ANOVA to test our results for statistical significance. We observed a significant increase in the average growth rate of both the wild type and the tla3 mutant with increasing light intensity (p-value = 2.05 x 10^-8). We also found that the reduction (in the photosynthetic apparatus) of photosynthetic pigments in the light-harvesting complexes from the deletion in the TLA3 gene caused the tla3 mutant to have a significantly lower average growth rate than the wild type at all the light intensities tested (p-value = 4.99 x 10^-7). There was a statistically significant difference in the effect of light intensity on the growth rate between the wild-type and the tla3 mutant C. reinhardtii (p-value = 1.84 x 10^-4). The average growth rate of the wild type increased sharply, whereas the tla3 mutant had a constant steady increase as light intensity increased.