Climate stress causes flower abortion in crops

Climate instability threatens the reproduction of cultivated plants. Heat and drought intensify reproductive abortion—loss of flowers, ovules, embryos, and seeds—and reduce grain yield. This phenomenon, regulated by genetic, hormonal, and environmental factors, affects essential crops such as cereals, legumes, and oilseeds.

In corn, up to 88% of seeds can be aborted by heat stress. In wheat, more than 70% of potential grains per spikelet fail to form. In 26% of ears evaluated in the Corn Belt region (USA), the apical tip aborted under heat and drought, with losses of up to 91%.

The data comes from a study by scientists at Texas Tech University, Oklahoma State University and North Carolina State University.

Stages vulnerable to abortion

Abortion can occur at various stages: from the development of floral primordia to embryo formation. Before fertilization, heat stress alters hormones, sugar metabolism, and assimilation distribution. This imbalance triggers the programmed death of female cells, such as synergids and eggs, leading to reproductive failure.

During fertilization, stress disrupts the interaction between pollen and pistil. The accumulation of reactive oxygen species (ROS) impairs pollen tube integrity and orientation, in addition to inducing premature cell death. After fertilization, embryo development may fail due to hormonal dysregulation and energy restriction.

Hormones out of balance

Floral survival depends on efficient carbohydrate distribution. In wheat, stalk elongation improves light capture and favors grain formation. In corn, drought reduces assimilates before anthesis and during grain filling, explaining 77% of yield variation. Tolerant genotypes maintain invertase activity, transport more sugars, and better discharge sucrose.

Hormones such as auxin, cytokinin (CK), abscisic acid (ABA), and jasmonate (JA) are involved in regulation. In wheat, basal spikelets abort more often because they contain less sucrose and higher levels of ABA and JA. Central spikelets, on the other hand, contain more CK and sugar, and have greater reproductive success.

In legumes, heat reduces the strength of the reproductive drain. In beans and soybeans, water deficit and heat stress cause flower abortion by compromising ovule development.

Arrested development

Egg miscarriage also results from genetic defects. In rice and soybeans, mutations in genes that regulate meiosis and embryo sac formation cause a high rate of miscarriage. Mitochondrial defects, RNA imbalances, or defects in ribosomal biogenesis affect the maturation of the female gametophyte and prevent embryo formation.

Heat distorts the hormonal gradients essential for ovule growth and induces ethylene production, which worsens abortion. In peas, heat stress increases the number of aborted ovules by up to 16%, mainly in the upper nodes of the plant.

Barriers to fertilization

Fertilization success depends on the precise interaction between pollen and pistil. Heat affects pollen viability, its adhesion to the stigma, and pollen tube elongation. In soybeans, temperatures between 35°C and 38°C reduce pollen germination, hinder anther dehiscence, and reduce stigma receptivity.

Drought, in turn, delays the synchronization between stigma emission and pollen release, as occurs in corn. Competition between ovaries for resources and the accumulation of ABA reduce floral receptivity. An external supply of cytokinins can partially reverse this effect.

Under combined heat and drought stress, damage intensifies. Carbohydrate shortages affect both the pollen tube and the ovary. The energy deficit, compounded by mitochondrial collapse and cytoskeletal disruption, impairs male gamete release and increases abortion rates.

After fertilization, new risks

Even after fertilization, the embryo faces risks. Mitochondrial function is essential for cell division and differentiation. Environmental stresses induce ROS accumulation and activate cell death pathways. In corn, mutations affecting mitochondrial ribosomal proteins result in early embryonic abortion.

Auxin guides the embryo's apical-basal axis. Changes in its production or transport affect tissue organization and disrupt development. Elevated levels of ABA and ethylene under stress reinforce cellular suppression pathways and increase the risk of miscarriage.

Transcriptional reprogramming also contributes. Growth genes are repressed, while stress response genes are activated. This metabolic redirection compromises embryogenesis.

Blocked sugars

The transport of sugars from the mother plant to the seed is blocked under stress. Even when sucrose is available, discharge into the reproductive tissues fails. Inhibition of invertases and SWEET transporters reduces carbon flow and causes abortion in up to 80% of soybean embryos.

In corn, drought reduces starch deposition by 42%. Heat decreases the activity of starch-synthesizing enzymes. Transport is further hampered by callose deposition, which narrows the vascular bundles.

Low sugar intake alters hormonal balance and increases the production of ethylene, one of the factors that induce miscarriage. Even so, ethylene alone does not cause miscarriage under normal conditions. The problem stems from the interaction between lack of energy, hormones, and stress signaling.

Further information at doi.org/10.1016/j.tplants.2025.08.015