Acclimation improves salt stress tolerance in Zea mays plants

Plants exposure to low level salinity activates an array of processes leading to an improvement of plant stress tolerance. Although the beneficial effect of acclimation was demonstrated in many herbaceous species, underlying mechanisms behind this phenomenon remain poorly understood. In the present study we have addressed this issue by investigating ionic mechanisms underlying the process of plant acclimation to salinity stress in Zea mays. Effect of acclimation were examined in two parallel sets of experiments: a growth experiment for agronomic assessments, sap analysis, stomatal conductance, chlorophyll content, and confocal laser scanning imaging; and a lab experiment for in vivo ion flux measurements from root tissues. Being exposed to salinity, acclimated plants (1) retain more K⁺ but accumulate less Na⁺ in roots; (2) have better vacuolar Na⁺ sequestration ability in leaves and thus are capable of accumulating larger amounts of Na⁺ in the shoot without having any detrimental effect on leaf photochemistry; and (3) rely more on Na⁺ for osmotic adjustment in the shoot. At the same time, acclimation affect was not related in increased root Na⁺ exclusion ability. It appears that even in a such salt-sensitive species as maize, Na⁺ exclusion from uptake is of a much less importance compared with the efficient vacuolar Na⁺ sequestration in the shoot.