Hubbart S, Peng S, Horton P, Chen Y, Murchie E H
Division of Agricultural and Environmental Science, School of Biosciences, University of Nottingham, Sutton Bonington, Loughborough, Leicestershire LE12 5RD, UK.
J Exp Bot. 2007;58(12):3429-38. doi: 10.1093/jxb/erm192. Epub 2007 Sep 17.
Crop improvement in terms of yield is rarely linked to leaf photosynthesis. However, in certain crop plants such as rice, it is predicted that an increase in photosynthetic rate will be required to support future grain yield potential. In order to understand the relationships between yield improvement and leaf photosynthesis, controlled environment conditions were used to grow 10 varieties which were released from the International Rice Research Institute (IRRI) between 1966 and 1995 and one newly developed line. Two growth light intensities were used: high light (1500 micromol m(-2) s(-1)) and low light (300 micromol m(-2) s(-1)). Gas exchange, leaf protein, chlorophyll, and leaf morphology were measured in the ninth leaf on the main stem. A high level of variation was observed among high light-grown plants for light-saturated photosynthetic rate per unit leaf area (P(max)), stomatal conductance (g), content of ribulose bisphosphate carboxylase-oxygenase (Rubisco), and total leaf protein content. Notably, between 1966 and 1980 there was a decline in P(max), g, leaf protein, chlorophyll, and Rubisco content. Values recovered in those varieties released after 1980. This striking trend coincides with a previous published observation that grain yield in IRRI varieties released prior to 1980 correlated with harvest index whereas that for those released after 1980 correlated with biomass. P(max) showed significant correlations with both g and Rubisco content. Large differences were observed between high light- and low light-grown plants (photoacclimation). The photoacclimation 'range' for P(max) correlated with P(max) in high light-grown plants. It is concluded that (i) leaf photosynthesis may be systematically affected by breeding strategy; (ii) P(max) is a useful target for yield improvements where yield is limited by biomass production rather than partitioning; and (iii) the capacity for photoacclimation is related to high P(max) values.
从产量方面来看，作物改良很少与叶片光合作用相关联。然而，在某些作物如水稻中，预计未来需要提高光合速率以支持粮食产量潜力。为了了解产量提高与叶片光合作用之间的关系，利用可控环境条件种植了10个于1966年至1995年间从国际水稻研究所（IRRI）发布的品种以及一个新培育的品系。使用了两种生长光照强度：高光（1500微摩尔·米⁻²·秒⁻¹）和低光（300微摩尔·米⁻²·秒⁻¹）。对主茎上的第九片叶子进行了气体交换、叶片蛋白质、叶绿素和叶片形态的测量。在高光生长的植株中，观察到单位叶面积的光饱和光合速率（P(max)）、气孔导度（g）、核酮糖二磷酸羧化酶加氧酶（Rubisco）含量和总叶片蛋白质含量存在高度变异。值得注意的是，在1966年至1980年间，P(max)、g、叶片蛋白质、叶绿素和Rubisco含量有所下降。1980年之后发布的那些品种的这些值有所恢复。这一显著趋势与之前发表的一项观察结果一致，即1980年之前发布的IRRI品种的粮食产量与收获指数相关，而1980年之后发布的品种的粮食产量与生物量相关。P(max)与g和Rubisco含量均呈显著相关。在高光和低光生长的植株之间观察到了很大差异（光驯化）。P(max)的光驯化“范围”与高光生长植株中的P(max)相关。得出的结论是：（i）叶片光合作用可能会受到育种策略的系统性影响；（ii）在产量受生物量生产而非分配限制的情况下，P(max)是提高产量的一个有用目标；（iii）光驯化能力与高P(max)值相关。
