Biochemistry and Cell Biology, Rice University, Houston, TX 77005-1892, USA.
Plant J. 2011 Oct;68(2):225-33. doi: 10.1111/j.1365-313X.2011.04680.x. Epub 2011 Jul 26.
Nitric oxide signals diverse responses in animals and plants. Whereas nitric oxide synthesis mechanisms in animals are well understood, how nitric oxide is synthesized and regulated in plants remains controversial. NOA1 is a circularly permuted GTPase that is important for chloroplast function and is implicated in nitric oxide synthesis. However, the reported consequences of a null mutation in NOA1 are inconsistent. Whereas some studies indicate that the noa1 mutant has severe reductions in nitric oxide accumulation, others report that nitric oxide levels are indistinguishable between noa1 and the wild type. Here, we identify a correlation between the reported ability of noa1 to accumulate nitric oxide with growth on sucrose-supplemented media. We report that noa1 accumulates both basal and salicylic acid-induced nitric oxide only when grown on media containing sucrose. In contrast, nitric oxide accumulation in wild type is largely insensitive to sucrose supplementation. When grown in the absence of sucrose, noa1 has low fumarate, pale green leaves, slow growth and reduced chlorophyll content. These phenotypes are consistent with a defect in chloroplast-derived photosynthate production and are largely rescued by sucrose supplementation. We conclude that NOA1 has a primary role in chloroplast function and that its effects on the accumulation of nitric oxide are likely to be indirect.
一氧化氮在动物和植物中传递着不同的信号。虽然动物中一氧化氮的合成机制已被充分了解，但植物中一氧化氮的合成和调控方式仍存在争议。NOA1 是一种环状排列的 GTPase，对叶绿体功能很重要，并且与一氧化氮的合成有关。然而，NOA1 缺失突变的报道后果并不一致。一些研究表明，noa1 突变体的一氧化氮积累严重减少，而另一些研究则报告说 noa1 和野生型之间的一氧化氮水平没有区别。在这里，我们发现了 noa1 积累一氧化氮的能力与在添加蔗糖的培养基上生长之间的相关性。我们报告说，只有在含有蔗糖的培养基上生长时，noa1 才能积累基础和水杨酸诱导的一氧化氮。相比之下，野生型中一氧化氮的积累对蔗糖的补充几乎不敏感。当在没有蔗糖的情况下生长时，noa1 会积累较少的延胡索酸，叶片呈浅绿色，生长缓慢，叶绿素含量降低。这些表型与叶绿体衍生的光合作用产物产生缺陷一致，并且在很大程度上可以通过蔗糖补充来挽救。我们得出结论，NOA1 在叶绿体功能中具有主要作用，并且其对一氧化氮积累的影响可能是间接的。
