Cytological studies on the incompatibility of protoplast fusion in crops

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1. Mesophyll protoplasts of mung bean and cell suspension-derived protoplasts of azuki bean were electrofused and examined by electron microscopy. Chloroplasts from mung bean and proplastids from azuki bean were grouped respectively and located on their original sides in fusion products. Elimination of chloroplasts was observed in some daughter cells.2. Effects of iodoacetamide (IOA) on azuki bean protoplasts were examined. IOA induced an overformation of rough endoplasmic reticulum which was followed by the collapse of cytoplasm. However, ultrastructural damages were mitigated if the IOA-treated protoplasts were fused with untreated mung bean protoplasts.3. Tobacco mesophyll protoplasts and soybean cell suspension-derived protoplasts were fused and cultured in various media in which division activity of parental protoplasts was differently affected. Elimination of tobacco chloroplasts from daughter cells was the highest in the medium profitable to division of soybean protoplasts but was not observed in the medium profitable to tobacco protoplasts.4. Intergeneric somatic hybrid calli were obtained through protoplast fusion between Celosia cristata (C_3 species) and Amaranthus tricolor (C_4 species). Isozyme analysis of acid phosphatase confirmed the hybridity of calli.In conclusion, incompatibility reaction was not observed in early processes of protoplast fusion even between remote species. Elimination of organelles seems to occur gradually due to unequal segregation of organelles during cell divisions.