EFFECTS OF FLOODING ON CARBOHYDRATE AND ABA LEVELS IN ROOTS AND SHOOTS OF ALFALFA

Alfalfa is sensitive to waterlogging, and its yields are significantly reduced under this condition. We investigated the effects of soil flo oding on free abscisic acid (ABA) accumulation in shoots and roots of alfalfa in relation to plant growth and stomatal conductance responses . The production of dry matter in alfalfa was significantly affected b y flooding mainly as a result of a rapid reduction in root growth. Sho ot dry matter accumulation was maintained during the first 10 d of tre atment and started to decline thereafter. Foliar concentration of the major mineral elements (N, P, K) was reduced by flooding, whereas only K concentration decreased in roots of flooded plants. Regrowth declin ed with duration of flooding and was less than 50% of controls after 2 weeks. While no changes in ABA concentration could be detected in flo oded roots, an increase was noted within a few days in leaves when com pared to unflooded controls. This increase in free ABA coincided with the accumulation of large quantities of starch in leaves and a rapid d ecline in leaf stomatal conductance. Our results support the suggestio n that leaf ABA originates from the leaf itself and may be accumulatin g along with starch as a result of reduced translocation to the roots. Our observation of large accumulations of sucrose in flooded roots ag rees with previous reports that supply of carbohydrates is not a limit ing factor to root anaerobic metabolism in flooded alfalfa.