四种作物光下暗呼吸速率降低的原因

Causes of decreasing mitochondrial respiration under light in four crops

以C3作物(小麦,Triticum aestivum和大豆,Glycine max)和C4作物(玉米,Zea mays和千穗谷,Amaranthus hypochondriacus)为例,探讨了其光下暗呼吸速率降低的原因。结果表明,2%O2条件下,CO2浓度为0时,叶室CO2浓度维持在0左右,而胞间CO2浓度(Ci)显著高于叶室CO2浓度。分析认为这是由于此时植物的暗呼吸仍在正常进行。因此,该测量条件下的表观光合速率应为CO2浓度为0时的光下暗呼吸速率(Rd)。CO2浓度为0时,不同光强下的Rd均随光强的升高而降低,且在低光强(50μmol·m–2·s–1)和高光强(2 000μmol·m–2·s–1)之间存在显著差异,说明光强对Rd具有较大影响。在2%O2条件下,经饱和光强充分活化而断光后,以上4种作物叶片的暗呼吸速率(Rn)均随着时间的推移而下降,说明光强并未抑制暗呼吸速率。试验结果表明,Rd的降低是由于CO2被重新回收利用所导致,CO2回收利用率随光强的升高而增大,从低光强(50μmol·m–2·s–1)到高光强(2000μmol·m–2·s–1),小麦、大豆、玉米和千穗谷的回收利用率范围变动分别为22.65%–52.91%、22.40%–55.31%、54.24%–87.59%和72.43%–90.07%。

Aims Despite the increasing attention given to the rate of mitochondrial respiration under light（Rd）, considerable confusion persists over whether mitochondrial respiration in the dark（Rn） is inhibited by light and whether Rd is affected by light intensity. The objective of this study is to test the hypotheses： 1） Rn is not inhibited by light; 2） the rate of Rd changes with light intensity; and 3） the photosynthetic refixation of CO2 produced by Rn accounts for the apparent disparity between Rd and Rn. Methods In the present study, 0.02 mol·mol–1 O2（i.e. 2% O2） was used to saturate Rn and to inhibit photorespiration（Rp）. By using combined gas exchange measurements and a low O2（2% O2） method, the post-illumination CO2 release rate of Rn, photosynthetic rate（Pn） in response to photosynthetically active radiation（PAR） in 2% O2 at either 380 or 0 μmol·mol–1 CO2, of C3（Triticum aestivum and Glycine max） and C4（Zea mays and Amaranthus hypochondriacus） plants, were measured. Important finding Rn was not inhibited by light. At 2% O2 and 0 μmol·mol–1 CO2, the measured parameters could be used to accurately estimate Rd when CO2 concentration was set for 0 μmol·mol–1. Rd decreased with increasing light intensity. Although Rd was lower in the dark, this could be accounted for by photosynthetic re-fixing of respiratory CO2. For all plants tested, CO2 recovery rates increased with increasing light intensity（from 50 and 2 000 μmol·m–2·s–1）.