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.
Highlights
Temperatures exceeding the threshold of crop tolerance disturbs plant growth and leads to severe yield loss in many crops, including field pea (Prasad et al 2015; Bueckert et al 2015; Bhandari et al 2016)
Four days of high temperature (35°C day/18°C night) significantly affected the stage of flower development across cultivars, but the magnitude depended on the reproductive node at which flowers were located (P=0.0305; Table 2)
Our study revealed that high temperature can disturb ovule and embryo sac development in plants
Summary
Temperatures exceeding the threshold of crop tolerance disturbs plant growth and leads to severe yield loss in many crops, including field pea (Prasad et al 2015; Bueckert et al 2015; Bhandari et al 2016). Experiments exploring plant nodal hierarchy have indicated that growth of both young (flower buds) and old reproductive structures (young fruits and seeds) can be halted under high temperature (Guilioni et al 1997, 2003). To explain this phenomenon, Guilioni et al (1997) pointed out that flower abortion in pea under high temperature (31°C, equivalent to natural conditions in the field) was associated with a mechanism of accelerated termination of the plant reproductive phase. Pollen function (within flower buds) was impaired if plants were exposed to heat (36°C)
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