Pollen Thermotolerance of Upland Cotton Related to Anther Structure and HSP Expression

Abstract

High temperature stress influences pollen grains development in upland cotton (Gossypium hirsutum L.) anthers, resulting in anthers with an abnormal structure and pollen grains with a low germination rate. To examine the thermotolerance mechanisms of pollen grains in upland cotton, we observed pollen germination rates, pollen grain ultrastructure, anther structure, and the expression of heat shock protein (HSP) genes in pollen grains after the plants were continuously exposed to high temperatures (36/30°C) in a phytotron for 8 h every day over a period of 10 d. After the high‐temperature treatment, the pollen germination percentage of the heat‐sensitive cultivar was reduced compared with the heat‐tolerant cultivar, and the structure of indehiscent anthers and the ultrastructure of pollen grains in the heat‐sensitive cultivar were more abnormal than that in the heat‐tolerant cultivar. There were more abnormal mitochondria, endoplasmic reticulum, and vacuoles as well as fewer starch granules in the pollen grains of the heat‐sensitive cultivar compared with the heat‐tolerant cultivar. The deformation of the pollen grain architecture may influence the pollen germination rate. The expression of the GhHSP90, GhHSP2, GhHSP7, and GhHSP8 genes was up‐regulated to a greater extent in the heat‐sensitive pollen grains compared with the heat‐tolerant pollen during and after the high temperature period. The up‐regulation of HSP gene expression may protect pollen grains from damage under high temperature stress (36/30°C). The structure of the anthers, ultrastructure of the pollen grains, and expression of HSP genes are related to the thermotolerance of pollen grains. These results provide a new approach for screening upland cotton cultivars for thermotolerance.