Sorghum (Sorghum bicolor) and its relatives in the grass tribe Andropogoneae bear their flowers in pairs of spikelets in which one spikelet (seed-bearing or sessile spikelet [SS]) of the pair produces a seed and the other is sterile or male (staminate). This division of function does not occur in other major cereals such as wheat (Triticum aestivum) or rice (Oryza sativa). Additionally, one bract of the SS spikelet often produces a long extension, the awn, that is in the same position as, but independently derived from, that of wheat and rice. The function of the sterile spikelet is unknown and that of the awn has not been tested in Andropogoneae. We used radioactive and stable isotopes of carbon, RNA sequencing of metabolically important enzymes, and immunolocalization of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) to show that the sterile spikelet assimilates carbon, which is translocated to the largely heterotrophic SS. The awn shows no evidence of photosynthesis. These results apply to distantly related species of Andropogoneae. Removal of sterile spikelets in sorghum significantly decreases seed weight (yield) by ~9%. Thus, the sterile spikelet, but not the awn, affects yield in the cultivated species and fitness in the wild species.

高粱 ( Sorghum bicolor ) 及其草族 Andropogoneae 中的近缘植物以成对的小穗形式开花，其中一个小穗（结籽或无梗小穗 [SS]）产生种子，另一个不育或雄性（雄花） ）。这种功能划分不会发生在其他主要谷物中，例如小麦（ Triticum aestivum ）或水稻（ Oryza sativa ）。此外，SS 小穗的一个苞片通常会产生一个长的延伸部分，即芒，其位置与小麦和水稻的位置相同，但独立地源自小麦和水稻。不育小穗的功能尚不清楚，芒的功能尚未在穿心草亚科中进行过测试。我们使用碳的放射性和稳定同位素、代谢重要酶的RNA测序以及核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）的免疫定位来表明不育小穗同化碳，碳易位到很大程度上异养的SS。芒没有显示出光合作用的证据。这些结果适用于Andropogonae 的远亲物种。去除高粱中的不育小穗会导致种子重量（产量）显着降低约 9%。因此，不育的小穗，而不是芒，影响栽培物种的产量和野生物种的适应性。