Evidence for differential photo-regulation of in vitro nitrate assimilation in barley (C3) and corn (C4) seedlings
2002
Goyal, S.S. | Sehtiya, H.L. (University of California, California (USA). Department of Agronomy and Science)
Effect of exposing barley and corn seedlings to light during the in vivo Nitrate (NO3) assimilation assay and / or during the period preceding the assay , was studied in 9-day old intact seedlings. The effect of exogenously supplied sucrose was also studied in order to separate the specific (direct) effects of light from those of carbohydrates. The seedlings used had not been exposed to any exogenous nitrogen during germination and growth and hence, were uninduced for nitrate reduction. Interestingly, light conditions during the assay period (current) determined the NO3- assimilation in corn whereas in barely light conditions preceding as well as during the assay, influenced NO3 - assimilation. In other words, light did not has any residual effect on NO3- assimilation in corn whereas in barley a residual effect of light appeared to exist. Under continuous light (light present prior to, ad during assay), 1% surcose in the ambient medium increased N)3 - assimilation similarly in both barely and corn (89% and 77%, respectively), but the corresponding increase due to sucrose in continuous darkness was much greater in barley (967%) than in corn (51%). The results strongly suggest that in barley the total carbohydrate pool, rather than light per se, plays a dominant role in NO3 assimilation, whereas specific/direct light effects and /or current photosynthates may be more important in corn. Since both species were able to assimilate some NO3 in darkness, light did not appear to be an absolute requirement for the assimilation of NO3 either in barley or in corn.
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