High temperatures disturb ovule development in field pea (Pisum sativum)

Abstract

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 temperatures on field pea ovules. We investigated the impact of heat on ovules of flowers at various reproductive nodes of field pea using growth chambers. We exposed 6 cultivars exhibiting diverse heat tolerance to 4 days of heat (35 °C day/18 °C night) during early flowering. Post-treatment ovules and embryo sacs were assessed using clearing by light microscopy 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. Whereas 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.