The role of bundle sheath conductance (g_bs) in sustaining sugarcane photosynthesis under nitrogen deficiency was investigated. Sugarcane was grown under different levels of nitrogen supply and g_bs was estimated using simultaneous measurements of leaf gas exchange and chlorophyll fluorescence at 21% or 2% [O₂] and varying air [CO₂] and light intensity. Maximum rates of PEPC carboxylation, Rubisco carboxylation, and ATP production increased with an increase in leaf nitrogen concentration (LNC) from 1 to 3 g m⁻². Low nitrogen supply reduced Rubisco and PEPC abundancies, the quantum efficiency of CO₂ assimilation and g_bs. Because of reduced g_bs, low photosynthetic rates were not associated with increased leakiness under nitrogen deficiency. In fact, low nitrogen supply increased bundle sheath cell wall thickness, probably accounting for low g_bs and increased estimates of [CO₂] at Rubisco sites. Effects of nitrogen on expression of ShPIP2;1 and ShPIP1;2 aquaporins did not explain changes in g_bs. Our data revealed that reduced Rubisco carboxylation was the main factor causing low sugarcane photosynthesis at low nitrogen supply, in contrast to the previous report on the importance of an impaired CO₂ concentration mechanism under N deficiency. Our findings suggest higher investment of nitrogen into Rubisco protein would favour photosynthesis and plant performance under low nitrogen availability.

研究了束鞘电导 ( g _bs ) 在缺氮条件下维持甘蔗光合作用的作用。甘蔗在不同的氮供应水平下生长，g _bs是通过同时测量叶片气体交换和叶绿素荧光在 21% 或 2% [O ₂ ] 以及不同的空气 [CO ₂ ] 和光强度下进行估算的。PEPC 羧化、Rubisco 羧化和 ATP 产生的最大速率随着叶氮浓度 (LNC) 从 1 到 3 g m ^{-2 的}增加而增加。低氮供应降低了 Rubisco 和 PEPC 的丰度、CO ₂同化和g _bs的量子效率. 由于g _bs降低，低光合速率与缺氮情况下的渗漏增加无关。事实上，低氮供应增加了束鞘细胞壁厚度，这可能解释了低g _bs和Rubisco 站点[CO ₂ ]估计值的增加。氮对Sh PIP2;1和Sh PIP1;2水通道蛋白表达的影响不能解释g _{bs 的}变化。我们的数据显示，减少的 Rubisco 羧化是导致低氮供应下甘蔗光合作用低的主要因素，这与之前关于受损 CO ₂N缺乏下的浓缩机制。我们的研究结果表明，在低氮可用性下，对 Rubisco 蛋白的更多氮投资将有利于光合作用和植物性能。