High temperature disturbs ovule development in field pea (Pisum sativum L.)
High temperatures affect reproductive growth and lead to yield loss in many crops. Field pea is heat sensitive, but little is known about the effect of high temperature on ovules. We investigated heat impact on ovules of flowers at various reproductive nodes of field pea using growth chambers. Six cultivars exhibiting diverse heat tolerance were exposed to four days of heat (35°C day/18°C night) during early flowering. Post-treatment ovules and embryo sacs were assessed employing clearing by light, and fluorescence, microscopy. Results indicated that greater ovule and embryo sac development occurred on some nodes, but poor ovule and embryo sac expansion resulted on other nodes of the same heat-treated plants. While advanced ovule and embryo sac development were identified on heat-tolerant cultivars, a combination of advanced and less advanced ovule and embryo sac development occurred in intermediate and heat-sensitive cultivars. More than 90% of the affected ovules displayed embryos at various stages of development, which indicated disruption around fertilization or shortly thereafter. Callose accumulation around the vascular bundle within ovules suggested disruption of assimilate transport to the embryo sac. The contrasting pattern of ovule development at different nodes implied a conflict between early aging and maternal supply of heat-treated plants.