Abstract
In temperate climates, most plants flower during the warmer season of the year to avoid negative effects of low temperatures on reproduction. Nevertheless, few species bloom in midwinter and early spring despite severe and frequent frosts at that time. This raises the question of adaption of sensible progamic processes such as pollen germination and pollen tube growth to low temperatures. The performance of the male gametophyte of 12 herbaceous lowland species flowering in different seasons was examined in vitro at different test temperatures using an easy to handle testing system. Additionally, the capacity to recover after the exposure to cold was checked. We found a clear relationship between cold tolerance of the activated male gametophyte and the flowering time. In most summer-flowering species, pollen germination stopped between 1 and 5 °C, whereas pollen of winter and early spring flowering species germinated even at temperatures below zero. Furthermore, germinating pollen was exceptionally frost tolerant in cold adapted plants, but suffered irreversible damage already from mild sub-zero temperatures in summer-flowering species. In conclusion, male gametophytes show a high adaptation potential to cold which might exceed that of female tissues. For an overall assessment of temperature limits for sexual reproduction it is therefore important to consider female functions as well.
Highlights
Among various environmental factors, temperature is one of the main factors shaping the geographical and elevational distribution of plants [1,2] and the temporal patterning of phenology [3].To colonize a habitat over the long term all developmental phases must be adapted to the prevailing temperature conditions
We found a clear relationship between cold tolerance of the activated male gametophyte and the flowering time
We focused on the performance of the male gametophyte which offers the advantage to examine a greater number of species using an in vitro test system
Summary
Temperature is one of the main factors shaping the geographical and elevational distribution of plants [1,2] and the temporal patterning of phenology [3].To colonize a habitat over the long term all developmental phases must be adapted to the prevailing temperature conditions. Among the reproductive phases male gametogenesis (reviewed in [4]) and anthesis is susceptible to unfavorable temperatures. The temperature range in which sexual processes normally operate varies among species and genotypes according to the climatic conditions in their habitat [5,11,12,13]. The cold limit for pollen germination and pollen tube growth was found above 10 ◦ C in plants from warmer climates [14,15], and between 5 and 10 ◦ C in most lowland plants in the temperate zone [13,16,17]. In high-mountain plants, which may experience sub-zero temperatures during the growing period, reproductive processes such as pollen germination, pollen tube growth, and fertilization still operate around
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