The response of broccoli plants to high temperature and possible role of root aquaporins

The effect of high root temperature on the water-uptake capability of broccoli plants (Brassica oleracea cv. Parthenon), the status of the plasma membrane and the role of aquaporins in water transport through the plant plasma membrane were investigated. For this, different temperatures (25, 35, 40 and 45 °C) were assayed. A decrease of the PIP1 and PIP2 aquaporins abundance with increasing temperature was observed, but the Pf values of protoplasts increased with the temperature. Changes of membrane fluidity were shown only at 40 °C, driving the membrane to a more rigid state. Also, the damaging effects of the stress, determined as electrolyte leakage (EL) in the whole root, and the possible osmotic adjustment, as an adaptive mechanism, were investigated. We propose that the increase in osmotic water permeability at higher temperature was not due to changes in the abundance of PIPs, but was probably due to an increase of permeability through the lipid bilayer. Also, the relation of the reduced gas exchange and aquaporins would provide a possible signal mechanism for acclimation to heat stress.