TPR domain coding gene ST2 may be involved in regulating tillering and fertility in rice

A decrease in the tiller number and male sterility will lead to a decline in the rice yield. Therefore, it is significant to study the molecular mechanism of controlling the tiller number and regulating the male reproductive development. The mutant st2 (single tiller 2) was induced by ethyl methane sulfonate (EMS) in the indica maintainer line Xinong 1B and showed single tillering and male sterility. I₂-KI staining showed that the st2 pollen was aborted. The scanning electron microscope (SEM) observation underlined that the anther of st2 became smaller, the wax of the epidermis reduced, the inner wall shrank and the Ubisch body decreased, the pollen collapsed, and the germination pore developed abnormally. The genetic analysis discovered that the trait was controlled by a single recessive nuclear gene located on chromosome 3. LOC_Os03g05540 encoding a tetratricopeptide repeat (TPR) domain was identified as the candidate gene by sequencing. The quantitative real-time polymerase chain reaction (qRT-PCR) analysis indicated that ST2 was highly expressed in the stem apical meristem (SAM) and the initial stage of meiosis during the anther development. The subcellular localisation indicated that ST2 is a nuclear and plasmic localisation protein. The homology analysis demonstrated that ST2 was evolutionarily conserved. These results laid a foundation for further study of the ST2 function.

Origin and structure of Ubisch bodies in Pinus sylvestris

In <em>Pinus sylvestris</em> Ubisch bodies are produced repeatedly, and each crop is formed at a distinct phase in the secretory cycles of tapetal cells. While each production has a Ubisch body wall similar to the then current state of the exine with regard to thickening and ornamentation, the survivers of previous productions do not change. Examples of all the structurally different Ubisch body wall forms can be seen when terminally, at the time of pollen shedding, the relict Ubisch bodies become spatially concentrated on the minimal surface area of the senescent cells of the tapetum. In angiosperms after one or a few periods of initiation Ubisch bodies may remain in association with the surface of tapetal cells where the Ubisch body wall undergoes changes like those of the maturing pollen exine. We conclude that as a consequence of Ubisch body detachment from the plasma membrane of tapetal cells there is in <em>Pinus sylvestris</em> no updated information for modification of the wall and the Ubisch body wall remains static.

The Ultrastructure and Ontogeny of Pollen in Helleborus Foetidus L

The ontogeny of the tapetum and Ubisch bodies in Helleborus foetidus L. has been examined at the ultrastructural level, and their development has been closely linked with that of the sporogenous cell and pollen grains. During development the tapetum passes through successive phases of synthesis, maturity and senescence, ending in complete dissolution. During the anabolic phase of growth, precursors of the Ubisch bodies are formed as spheroidal vesicles of medium electron density within the tapetal cytoplasm; they are associated with a zone of radiating ribosomes, which, as development proceeds, can clearly be seen to be situated on strands of endoplasmic reticulum. The callose special wall round the microspores and the tapetal cell wall now disintegrate and the pro-Ubisch bodies are extruded through the cell membrance of the tapetal cells, where they remain on the surface of the anther cavity and soon become irregularly coated with sporopollenin. Deposition of sporopollenin continues on the Ubisch bodies at the same time as upon the exines of the developing pollen grains. In both cases, the later stages of sporopollenin deposition are associated with electron-transparent layers of unit-membrane dimensions appearing in section as white lines of uniform thickness. Continuing deposition of sporopollenin leads to the formation of compound or aggregate Ubisch bodies. It is conjectured that the sporopollenin is synthesized from the compounds of low molecular weight released into the anther loculus by the breakdown of the callose special wall and the tapetal cell wall. The final stages of tapetal autolysis involve the disappearance of all the cell organelles. An attempt is made to relate the findings to those described in other recent studies on Ubisch body formation and to combine them in a common ontogenetic pattern.