The role of the integuments in pollen tube guidance in flowering plants

Abstract

In angiosperms, pollen tube entry into the ovule generally takes place through the micropyle, but the exact role of the micropyle in pollen tube guidance remains unclear. A limited number of studies have examined eudicots with bitegmic micropyles, but information is lacking in ovules of basal/early-divergent angiosperms with unitegmic micropyles. We have evaluated the role of the micropyle in pollen tube guidance in an early-divergent angiosperm (Annona cherimola) and the evolutionarily derived Arabidopsis thaliana by studying γ-aminobutyric acid (GABA) and arabinogalactan proteins (AGPs) in wild-type plants and integument-defective mutants. A conserved inhibitory role of GABA in pollen tube growth was shown in A. cherimola, in which AGPs surround the egg apparatus. In Arabidopsis, the micropyle formed only by the outer integument in wuschel-7 mutants caused a partial defect in pollen tube guidance. Moreover, pollen tubes were not observed in the micropyle of an inner no outer (ino) mutant in Arabidopsis, but were observed in homologous ino mutants in Annona. The similar distribution of GABA and AGPs observed in the micropyle of Arabidopsis and Annona, together with the anomalies from specific integument mutants, support the role of the inner integument in preventing multiple tube entrance (polytubey) in these two phylogenetically distant genera.

Functional conservation of the grapevine candidate gene INNER NO OUTER for ovule development and seed formation

“…However, despite findings in Annona crop, in Arabidopsis ino-1 , as previously mentioned, “fruit” development appears as compromised 18 , 19 . The different effect of ino defects in ovule development and on seeds and fruit production in Annona and Arabidopsis species has been the subject of further characterizations 12 , 40 . In these studies, the Arabidopsis ino-1 pollen tubes grow through the transmitting tract but were never observed inside the micropyle, and the majority of ovules fail to form embryo sacs.…”

Acid invertase confers heat tolerance in rice plants by maintaining energy homoeostasis of spikelets

“…Pollen germination and pollen tube elongation are complex processes, which are always determined by the energy status and by guiding signalling (Lamport, Tan, Held, & Kieliszewski, ; Lora, Laux, & Hormaza, ). This process is disturbed by heat stress, which results in pollination failure (Muhlemann, Younts, & Muday, ; Zhang et al, ).…”

Natural Variation in Ovule Morphology Is Influenced by Multiple Tissues and Impacts Downstream Grain Development in Barley (Hordeum vulgare L.)

“…“Extra” germline cells in rice typically enter meiosis, but this is not the case in Arabidopsis . This may reflect a specific feature of the larger nucellus in rice and its ability to provide more stimulatory signals for germline development (Nonomura et al, 2003;Lora et al, 2019).…”