Changes in plasmodesmata frequency in vascular bundles of maize seedling leaf induced by growth at sub-optimal temperatures in relation to photosynthesis and assimilate export

Abstract

The frequency of plasmodesmata at the cell interfaces important for C4 photosynthesis was studied in two inbred lines of maize, KW 1074 (flint, chilling-tolerant) and CM 109 (dent, chilling-sensitive), grown until the third leaf stage at sub-optimal temperature (14/12 °C) in relation to the photosynthesis and assimilate export. The number of plasmodesmata linking mesophyll and bundle sheath as well as bundle sheath and parenchyma cells in the third leaf increased in both lines compared to control leaves at the same physiological stage grown at the optimal temperature (24/22 °C). The number of plasmodesmata on the mesophyll–bundle sheath interface increased relatively more in the KW 1074 line than in CM 109. At the sub-optimal temperature, there was also an increase in the plasmodesmata frequency between vascular parenchyma cells, but only in KW 1074 the differences were statistically significant. Plants of both lines grown at low temperature exhibited a decrease of Φ PSII. However, the light response curve of Φ PSII as well as the gas exchange rate in leaves of plants grown at sub-optimal temperature showed values higher in the KW 1074 than in the CM 109 line. KW 1074 seedlings also showed shorter the time interval between 14C incorporation into a leaf and 14C-assimilate appearance in the transport path. The genotypic difference in the photosynthetic competence of plants grown at sub-optimal temperatures might thus be related to the ability to increase the number of plasmodesmata at the interfaces between mesophyll, bundle sheath, and parenchyma cells. Such an increase in plasmodesmata density enable more efficient exchange of photosynthetic metabolites as well as export of sucrose at the temperatures which slow down the diffusion from cell to cell.