Kolbe Allison R, Studer Anthony J, Cousins Asaph B
School of Biological Sciences, PO Box 644236, Washington State University, Pullman, WA 99164, USA.
Department of Crop Sciences, 1201 West Gregory Drive, Edward R. Madigan Laboratory 289, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA.
Funct Plant Biol. 2018 Apr;45(5):489-500. doi: 10.1071/FP17265.
Carbon isotope discrimination is used to study CO2 diffusion, substrate availability for photosynthesis, and leaf biochemistry, but the intraspecific drivers of leaf carbon isotope composition (δ13C) in C4 species are not well understood. In this study, the role of photosynthetic enzymes and post-photosynthetic fractionation on δ13C (‰) was explored across diverse maize inbred lines. A significant 1.3‰ difference in δ13C was observed between lines but δ13C did not correlate with in vitro leaf carbonic anhydrase (CA), phosphoenolpyruvate carboxylase (PEPC), or ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity. RNA-sequencing was used to identify potential differences in post-photosynthetic metabolism that would influence δ13C; however, no correlations were identified that would indicate significant differences in post-photosynthetic fractionation between lines. Variation in δ13C has been observed between C4 subtypes, but differential expression of NADP-ME and PEP-CK pathways within these lines did not correlate with δ13C. However, co-expression network analysis provided novel evidence for isoforms of C4 enzymes and putative transporters. Together, these data indicate that diversity in maize δ13C cannot be fully explained by variation in CA, PEPC, or Rubisco activity or gene expression. The findings further emphasise the need for future work exploring the influence of stomatal sensitivity and mesophyll conductance on δ13C in maize.
碳同位素分馏被用于研究二氧化碳扩散、光合作用的底物可利用性以及叶片生物化学，但C4植物叶片碳同位素组成（δ13C）的种内驱动因素尚未得到很好的理解。在本研究中，我们在不同的玉米自交系中探讨了光合酶和光合后分馏对δ13C（‰）的作用。品系间δ13C存在1.3‰的显著差异，但δ13C与体外叶片碳酸酐酶（CA）、磷酸烯醇式丙酮酸羧化酶（PEPC）或核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）活性无关。RNA测序被用于识别可能影响δ13C的光合后代谢差异；然而，未发现表明品系间光合后分馏存在显著差异的相关性。在C4亚型之间已观察到δ13C的变化，但这些品系中NADP-ME和PEP-CK途径的差异表达与δ13C无关。然而，共表达网络分析为C4酶和假定转运蛋白的同工型提供了新证据。总之，这些数据表明，玉米δ13C的多样性不能完全由CA、PEPC或Rubisco活性或基因表达的变化来解释。这些发现进一步强调了未来有必要开展工作，探索气孔敏感性和叶肉导度对玉米δ13C的影响。
