Low temperature treatments of rice (Oryza sativa L.) anthers changes polysaccharide and protein composition of the anther walls and increases pollen fertility and callus induction

To understand the relationship between pollen fertility and callus induction from anthers of rice (Oryza sativa L.) during low-temperature treatment (LTT), F1 progeny of the cross ‘Nanjing 46’ × ‘Zaxima’ was used as materials. The pollen fertility, callus induction from anther and the histochemical and ultrastructural study of developing anthers from the rice plants with LTT was investigated. With LTT for 1–6 days before anther inoculation with callus induction medium, pollen fertility was maintained at 4 %. A moderate duration of LTT for 1–5 days and addition of exogenous plant growth regulators, 2,4-D from 1–2 mg L⁻¹, or 0.3 mg L⁻¹KT, enhanced callus induction from anthers. A moderate duration of LTT altered the insoluble polysaccharide content in the anther wall. Compared with the untreated control at 25 °C, the insoluble polysaccharide content dramatically decreased in the anther wall within the first 2 days of LTT, and thereafter increased and peaked on the fifth day of LTT. On the fifth day of LTT, the protein content in the anther wall declined. No change in lipid content was observed during LTT. Electron microscopy showed that for the first 5 days of LTT, the integrity of the four-layer anther wall structure was maintained, and large numbers of cell organelles such as Golgi apparatus, endoplasmic reticulum and mitochondria were observed in the developing pollen grains. Plentiful amount of amyloplasts were also observed on the fourth day of LTT. At 7 days of LTT, the anther wall had been degraded to a single epidermal layer and the internal layers had disappeared. Thus, LTT for up to 5 days before anther inoculation in the IM medium may delay degradation of the innermost layer of the anther wall, the tapetum by altering the insoluble polysaccharide and protein contents in the anther wall.