Differences between C3 (Hordeum vulgare L.) and C4 (Panicum miliaceum L.) plants with respect to their resistance to water deficit

Abstract

C4 photosynthetic pathway has an advantage over the C3 photosynthesis in arid environments due to a CO2 concentrating mechanism, enabling prolonged stomatal closure. However, the question arises if the metabolic limitations do not outweigh the stomatal limitations in the case of a severe water deficit. The aim of this research is to investigate the differences of drought resistance between C3 plant spring barley (Hordeum vulgare L.) and C4 plant common millet (Panicum miliaceum L.) according to the impact of relatively slight and severe drought on growth, photosynthetic apparatus and membrane oxidative damage. The growth of the millet plants was impaired more seriously than that of the barley plants. The height of slight or severe drought-treated barley decreased by 5.0% and 15.4% of control level, compared to the height decreased by 18.7% and 28.9% respectively for the millet plants. No statistically significant decrease in shoot dry weigh was detected after slight drought, whereas the strong drought reduced accumulation of shoot dry biomass of barley and millet by 12.7% and 17.7%, respectively. The photosynthetic rate of the millet plants was less affected in comparison to barley. Considerably lower stomatal conductance, transpiration rate, intercellular CO2 concentration, lipid peroxidation and higher water use efficiency (WUE) were detected for the millet plants. However, the growth and the photosynthetic rate of barley plants were more able to recover during the period of re-watering. Our results suggest that the advantages of the C4 photosynthetic pathway could lead to higher drought resistance due to lower oxidative stress (determined by an absence of photorespiration) and higher WUE. On the other hand, the contribution of non-stomatal and redox-independent limitations of growth remains to be elucidated.