Oakley Jason C, Sultmanis Stefanie, Stinson Corey R, Sage Tammy L, Sage Rowan F
Department of Ecology and Evolutionary Biology, The University of Toronto, 25 Willcocks Street, Toronto, ON M5S3B2 Canada.
Department of Ecology and Evolutionary Biology, The University of Toronto, 25 Willcocks Street, Toronto, ON M5S3B2 Canada
J Exp Bot. 2014 Jul;65(13):3637-47. doi: 10.1093/jxb/eru106. Epub 2014 Mar 27.
We crossed the C3 species Atriplex prostrata with the C4 species Atriplex rosea to produce F1 and F2 hybrids. All hybrids exhibited C3-like δ(13)C values, and had reduced rates of net CO2 assimilation compared with A. prostrata. The activities of the major C4 cycle enzymes PEP carboxylase, NAD-malic enzyme, and pyruvate-Pi dikinase in the hybrids were at most 36% of the C4 values. These results demonstrate the C4 metabolic cycle was disrupted in the hybrids. Photosynthetic CO2 compensation points (Г) of the hybrids were generally midway between the C3 and C4 values, and in most hybrids were accompanied by low, C3-like activities in one or more of the major C4 cycle enzymes. This supports the possibility that most hybrids use a photorespiratory glycine shuttle to concentrate CO2 into the bundle sheath cells. One hybrid exhibited a C4-like Г of 4 µmol mol(-1), indicating engagement of a C4 metabolic cycle. Consistently, this hybrid had elevated activities of all measured C4 cycle enzymes relative to the C3 parent; however, C3-like carbon isotope ratios indicate the low Г is mainly due to a photorespiratory glycine shuttle. The anatomy of the hybrids resembled that of C3-C4 intermediate species using a glycine shuttle to concentrate CO2 in the bundle sheath, and is further evidence that this physiology is the predominant, default condition of the F2 hybrids. Progeny of these hybrids should further segregate C3 and C4 traits and in doing so assist in the discovery of C4 genes using high-throughput methods of the genomics era.
我们将C3物种平卧滨藜与C4物种玫瑰滨藜杂交，产生了F1和F2杂种。所有杂种均表现出类似C3的δ(13)C值，与平卧滨藜相比，其净CO2同化率降低。杂种中主要C4循环酶磷酸烯醇式丙酮酸羧化酶、NAD-苹果酸酶和丙酮酸磷酸双激酶的活性最高仅为C4值的36%。这些结果表明杂种中的C4代谢循环被破坏。杂种的光合CO2补偿点(Г)一般介于C3和C4值之间，并且在大多数杂种中，一种或多种主要C4循环酶具有低的、类似C3的活性。这支持了大多数杂种利用光呼吸甘氨酸穿梭将CO2浓缩到维管束鞘细胞中的可能性。一个杂种表现出4 µmol mol(-1)的类似C4的Г，表明参与了C4代谢循环。与此一致的是，相对于C3亲本，该杂种所有测定的C4循环酶活性均升高；然而，类似C3的碳同位素比率表明低Г主要是由于光呼吸甘氨酸穿梭。杂种的解剖结构类似于使用甘氨酸穿梭将CO2浓缩在维管束鞘中的C3-C4中间物种，这进一步证明这种生理状态是F2杂种的主要默认状态。这些杂种的后代应进一步分离C3和C4性状，从而有助于利用基因组学时代的高通量方法发现C4基因。
