College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, PR China.
Plant Cell Physiol. 2012 May;53(5):892-900. doi: 10.1093/pcp/pcs032. Epub 2012 Mar 19.
The phenomenon whereby ammonium enhances the tolerance of rice seedlings (Oryza sativa L., cv. 'Shanyou 63' hybrid indica China) to water stress has been reported in previous studies. To study the intrinsic mechanism of biomass synthesis related to photosynthesis, hydroponic experiments supplying different nitrogen (N) forms were conducted; water stress was simulated by the addition of polyethylene glycol. Water stress decreased leaf water potential (Ψ(leaf)) under nitrate nutrition, while it had no negative effect under ammonium nutrition. The decreased Ψ(leaf) under nitrate nutrition resulted in chloroplast downsizing and subsequently decreased mesophyll conductance to CO(2) (g(m)). The decreased g(m) and stomatal conductance (g(s)) under nitrate nutrition with water stress restrained the CO(2) supply to the chloroplast and Rubisco. The relatively higher distribution of leaf N to Rubisco under ammonium nutrition might also be of benefit for photosynthesis under water stress. In conclusion, chloroplast downsizing induced a decline in g(m), a relatively higher decrease in g(s) under nitrate nutrition with water stress, restrained the CO(2) supply to Rubisco and finally decreased the photosynthetic rate.
先前的研究报道了铵态氮增强水稻幼苗（籼稻杂交品种汕优 63）对水分胁迫耐受性的现象。为了研究与光合作用相关的生物量合成的内在机制，进行了供应不同氮（N）形式的水培实验；通过添加聚乙二醇模拟水分胁迫。在硝态氮营养下，水分胁迫降低了叶片水势（Ψ（leaf）），而在铵态氮营养下则没有负面影响。硝态氮营养下Ψ（leaf）的降低导致叶绿体缩小，随后降低了 CO2 通过质膜的导度（g(m)）。在水分胁迫下，由于硝态氮营养导致 g(m)和气孔导度（g(s））降低，从而限制了 CO2 向叶绿体和 RuBP 羧化酶的供应。在水分胁迫下，铵态氮营养下叶片 N 向 RuBP 羧化酶的相对较高分配可能也有利于光合作用。总之，叶绿体缩小导致 g(m)下降，在水分胁迫下硝态氮营养中 g(s)的相对下降更大，限制了 CO2 向 RuBP 羧化酶的供应，最终降低了光合速率。
