Arabidopsis thaliana hybrids have similar properties to hybrid crops, with greater biomass relative to the parents. We asked whether the greater biomass was due to increased photosynthetic efficiency per unit leaf area or to overall increased leaf area and increased total photosynthate per plant. We found that photosynthetic parameters (electron transport rate, CO2 assimilation rate, chlorophyll content, and chloroplast number) were unchanged on a leaf unit area and unit fresh weight basis between parents and hybrids, indicating that heterosis is not a result of increased photosynthetic efficiency. To investigate the possibility of increased leaf area producing more photosynthate per plant, we studied C24×Landsberg erecta (Ler) hybrids in detail. These hybrids have earlier germination and leaf growth than the parents, leading to a larger leaf area at any point in development of the plant. The developing leaves of the hybrids are significantly larger than those of the parents, with consequent greater production of photosynthate and an increased contribution to heterosis. The set of leaves contributing to heterosis changes as the plant develops; the four most recently emerged leaves make the greatest contribution. As a leaf matures, its contribution to heterosis attenuates. While photosynthesis per unit leaf area is unchanged at any stage of development in the hybrid, leaf area is greater and the amount of photosynthate per plant is increased.

中文翻译：

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早期发育中的叶片生长是拟南芥生物量杂种优势的关键。

拟南芥杂交种具有与杂交作物相似的特性，相对于亲本具有更高的生物量。我们询问更大的生物量是由于每单位叶面积的光合作用效率提高还是整体叶面积增加和单株总光合产物增加所致。我们发现，亲本和杂种之间的叶单位面积和单位新鲜重量基础上的光合作用参数（电子传输速率，CO2同化率，叶绿素含量和叶绿体数量）没有变化，这表明杂种优势并不是提高光合效率的结果。为了研究增加叶面积每株植物产生更多光合产物的可能性，我们详细研究了C24×Landsberg erecta（Ler）杂种。这些杂种比亲本具有更早的发芽和叶片生长，在植物发育的任何时候导致更大的叶面积。杂种的发育叶明显大于亲本，因此光合产物的产量更高，对杂种优势的贡献增加。导致杂种优势的叶子随植物的生长而变化；最近出现的四片叶子贡献最大。随着叶片的成熟，其对杂种优势的贡献减弱。尽管杂种在发育的任何阶段每单位叶面积的光合作用没有变化，但叶面积却更大，每株植物的光合产物数量也增加了。从而增加了光合产物的产量，并增加了对杂种优势的贡献。导致杂种优势的叶子随植物的生长而变化；最近出现的四片叶子贡献最大。随着叶片的成熟，其对杂种优势的贡献减弱。尽管杂种在发育的任何阶段每单位叶面积的光合作用没有变化，但叶面积却更大，每株植物的光合产物数量也增加了。从而增加了光合产物的产量，并增加了对杂种优势的贡献。导致杂种优势的叶子随植物的生长而变化；最近出现的四片叶子贡献最大。随着叶片的成熟，其对杂种优势的贡献减弱。尽管杂种在发育的任何阶段每单位叶面积的光合作用没有变化，但叶面积却更大，每株植物的光合产物数量也增加了。