Carbon/nitrogen interactions during ear and kernel development of maize

The interdependence of C and N metabolism in achieving maximum reproductive development of maize is well known, but poorly understood. Our experimental approach has been to use stem infusion and in vitro kernel culture to control and/or abruptly change the supply of C and N assimilates available for ear and kernel development. A major goal of this research has been to ascertain whether kernel growth and composition is determined by the assimilate supply from the vegetation, or by factors operating within the kernel. For in vitro grown kernels, endosperm sugar status was closely related to C supply, and a supply of N allowed the kernel to use this assimilate for growth. Nitrogen-induced utilization of C was associated with concomitant increases in invertase activity, while high endosperm sugar (induced by either high media sucrose or low media N) resulted in low invertase activity. Stem-infused N, but not sucrose, caused subtle but distinct effects on the initial levels of endosperm assimilates, and on some enzymes of C and N metabolism, in a mariner consistent with the idea that N facilitates the kernel's utilization of sugars. These differences were also reflected in the final grain weight as infusion with N partially reversed the negative effects of N deficiency, while sucrose did not. Collectively, the data suggest that N plays a direct role in reproductive development in maize, in part by controlling the ability of the kernel to use C.