To reach the female gametophyte, growing pollen tubes must penetrate different tissues within the pistil, the female reproductive organ of a flower. Past research has identified various chemotropic cues that guide pollen tubes through the transmitting tract of the pistil, which represents the longest segment of its growth path. In addition, physical mechanisms also play a role in pollen tube guidance; however, these processes remain poorly understood. Here we show that pollen tubes from plants with solid transmitting tracts actively respond to the stiffness of the environment. We found that pollen tubes from Nicotiana tabacum and other plant species with a solid or semisolid transmitting tract increase their growth rate in response to an increasing matrix stiffness. By contrast, pollen tubes from Lilium longiflorum and other plant species with a hollow transmitting tract decrease their growth rate with increasing matrix stiffness, even though the forces needed to maintain a constant growth rate remain far below the maximum penetration force these pollen tubes are able to generate. Moreover, when confronted with a transition from a softer to a stiffer matrix, pollen tubes from N. tabacum display a greater ability to penetrate into a stiffer matrix compared with pollen tubes from L. longiflorum, even though the maximum force generated by pollen tubes from N. tabacum (11 µN) is smaller than the maximum force generated by pollen tubes from L. longiflorum (36 µN). These findings demonstrate a mechano-sensitive growth behavior, termed here durotropic growth, that is only expressed in pollen tubes from plants with a solid or semisolid transmitting tract and thus may contribute to an effective pollen tube guidance within the pistil.

为了到达雌配子体，生长的花粉管必须穿透雌蕊（花的雌性生殖器官）内的不同组织。过去的研究已经确定了引导花粉管通过雌蕊传播道的各种趋化性线索，雌蕊代表了其生长路径的最长部分。此外，物理机制也在花粉管引导中发挥作用；然而，人们对这些过程仍然知之甚少。在这里，我们展示了来自具有固体传播束的植物的花粉管对环境的硬度做出积极的反应。我们发现，来自烟草和其他具有固体或半固体传输道的植物物种的花粉管随着基质刚度的增加而增加其生长速率。相比之下，来自长花百合和其他具有中空传输道的植物物种的花粉管随着基质刚度的增加而降低其生长速率，即使维持恒定生长速率所需的力仍然远低于这些花粉管能够的最大穿透力产生。此外，当面临从较软基质到较硬基质的转变时，与长花草花粉管相比，烟草花粉管表现出更强的穿透到较硬基质的能力，即使由长花草花粉管产生的最大力N. tabacum (11 µN) 小于L. longiflorum花粉管产生的最大力 (36 µN)。 这些发现证明了机械敏感的生长行为，此处称为硬质生长，仅在具有固体或半固体传输道的植物的花粉管中表达，因此可能有助于雌蕊内有效的花粉管引导。