POLLEN-TUBE GROWTH AND EARLY EMBRYOGENESIS IN WHEAT X MAIZE CROSSES INFLUENCED BY 2,4-D

Pollen tube growth and embryogenesis were investigated in the intergen eric Triticum aestivum x Zea mays cross. Emasculated wheat florets wer e pollinated with maize pollen, and at one day after pollination, the wheat plants were injected with 2,4-dichlorophenoxyacetic acid (2,4-D) . Thr influence of 2,4-D on pollen tube behaviour was determined apply ing callose staining in whole mount preparations of pistils. Changes i n the embryo sac and early embryogenesis were analysed on sections aft er various histochemical stainings. Maize pollen tubes germinated with in 30 min and grew much slower through the pollen tube pathway compare d with selfings of both maize and wheat. Deviations in pollen tube gro wth occurred such as coiling, widening and forking, irrespective of tr eatment with 2,4-D. Pollen tubes reached the micropyle between 5 and 2 4 h after pollination. 2,4-D treatment increased the number of the pol len tubes that reached the micropyle, and additionally, multiplication of sperm cells was found in the maize pollen tubes. Embryo formation was analysed at 2 d after pollination. Only when pollen tubes were in the micropyle, zygotes and embryos were observed. This points to their hybrid origin. Moreover, the embryos are likely of zygotic origin sin ce multicellular embryos exhibited micronuclei, a sign of chromosome e limination not occurring in parthenogenic embryos and leading to haplo idy of the embryos. Treatment with 2,4-D increased successful intergen eric fertilization from 18.7 to 69.3%. Immature embryos were rescued b y in vitro culture from 14% of pollinated florets when excised at 14 d after pollination. (C) 1996 Annals of Botany Company.