Cytological Studies on Microsporogenesis and Male Gametophyte Development in a Cucumis Allotriploid Derived from Cucumis hytivus×C. sativus

Abstract

Microsporogenesis and male gametophyte development of a Cucumis allotriploid from meiosis of PMCs to mature pollen grains were studied using light microscopy. Variable chromosome configurations, e.g. univalents, bivalents, trivalents, quadrivalents, etc. were observed in most PMCs of the allotriploid at MI. Chromosome lagging and bridges at anaphase resulted from irregular chromosome separation and asynchronization between C and H genomes were frequently observed as well, which led to formation of polyads and inviable gametes. However, there were still some PMCs in which the normal meiotic process could be accomplished to form the microspore tetrads via simultaneous cytokinesis. The arrangement of microspores in the tetrads was tetrahedral. Among those microspores, part of them (10%) could develop into fertile gametophytes with 2 cells and 3 germ pores through the following stages: single-nucleus early stage, single-nucleus late stage, 2-celled stage after pollen mitosis. A few 3-celled pollens were also observed. But most other microspores (90%) were sterile stopped at single-nucleus stage. The low fertility of male gametophytes was confirmed by the weak stainability and low germination rate.