Sucrose synthesis and translocation in Zea mays L. during early growth, when subjected to N and K deficiency

Abstract

By omitting N and K either separately or in combination from the rooting medium, a nutrient stress condition was created with the aim of ascertaining whether sucrose synthesis or its translocation was linked to nutrient availability (N, K) in young maize plants. Sucrose and glucose levels as well as SPS activity measured over a six-week growth period showed no significant differences in leaves between the control and both the N- and K- stressed plants. Subsequently, the two top leaves of four-week old control and stressed plants were pulselabelled with [U-14C]-glucose for 24 hours and the translocation of radioactivity to stems and roots measured. K-stressed plants translocated less than 40 of the absorbed radioactivity from the leaves to the stems and roots and also tended to translocate more sucrose to the roots while much less was off-loaded in the storage tissue of the stems. Translocation of sucrose as well as radioactivity from leaves to stems and roots in N-stressed plants paralleled that of control plants. It is concluded that the total sucrose pools in leaves and roots, during the early growth of maize, is not necessarily a reflection of the crop's stress status caused by the depletion of different nutrients. However, in stems of K-stressed plants both the sucrose content and translocated radioactivity was almost 50% less compared to both the control and N-stressed plants supporting the assumption that K-depletion greatly inhibited sucrose translocation.