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Table 2 Comparisons of microsporogenesis, pollen development and pollen dispersal among four spray cut chrysanthemum cultivars

From: Factors affecting quantity of pollen dispersal of spray cut chrysanthemum (Chrysanthemum morifolium)

Stage

Major events in pollen development and pollen dispersal of ‘Qx-097’

The differences of ‘Noa’, ‘Qx-115’ and ‘Kingfisher’ compared with ‘Qx-097’

Microsporocyte formation stage

Tissue differentiation, microspore mother cells in irregular shape, tightly abutting, relatively large nuclei, formation of 4 complete anther walls.

None.

Microsporocyte meiosis stage

Oval-shaped microspore mother cells, meiosis, microspores in tetrahedral tetrads, microspore mother cells and tetrads surrounded by callose and abundant cytoplasm contains mitochondria, plastids, endoplasmic reticulum, small vacuoles, vacuolation of cytoplasm of endothecium layer and epidermal layer cells, condensed cytoplasm of tapetal layer cells.

‘Kingfisher: asymmetrical dyad and tetrad formed by inequality meiosis, degradation and vacuolization of microspore cytoplasm in tetrad, abnormal degradation and microspores not released from tetrads.

Early microspore stage

Free microspores released from tetrads, no vacuoles, no germ pores, thin cell wall, uniform and dense cytoplasm, nuclei in center of cells. vacuolation of cytoplasm of tapetal layer with discohesive cells increase, middle layer in further degradation;

‘Kingfisher’: nothing in pollen sacs, pollen abortion completely;

‘Noa’: individual microspore abortion.

Middle microspore stage

Microspore enlargement, germ pores formation, cells wall thickenings formed, spiked protuberances formed and inner wall formed, vacuoles increase and enlargement, degradation of microspore cytoplasm, off-centre of nuclei, tapetal layer cells radial thinning.

‘Qx-115’: large number of microspore abortion, cells broken, degradation of cytoplasm;

‘Noa’: individual microspore abortion;

‘Kingfisher’: nothing in pollen sacs.

Late microspore stage

Cell walls thickened and cells enlargement continues, large central vacuole formation, nuclei and cytoplasm at opposite side of germ pores against outer walls, tapetal layer cells in hill-shaped and further degradation, middle layer almost disappeared.

‘Qx-115’: microspore abortion continues, few complete pollen grains in the late microspore stage;

‘Noa’: individual microspore abortion;

‘Kingfisher’: nothing in pollen sacs.

Early bicellular pollen stage

Inequality mitosis of microspore, vegetative cell and generative cell formation, remains of tapetal layer, endothecium layer cells enlargement.

Anthers start shriveling of ‘Qx-115’ and ‘Kingfisher’.

Late bicellular pollen stage

Bicellular pollen stage enlargement, move of generative cell to vegetative cell, starch accumulation, ‘U’ shaped thickened of endothecium layer cell walls.

Anthers shriveled of ‘Qx-115’ and ‘Kingfisher’.

Mature pollen stage

The contents like starch fill the whole cytoplasm, generative cell dividing, sperm cells and mature pollen formation, non observation of 3-nuclei structure.

Anthers shriveled of ‘Qx-115’ and ‘Kingfisher’.

Anther cracking and pollen dispersing stage

Anther cracking, pollen dispersing, very high degree of anther cracking, pollen dispersing completely.

‘Noa’: the degree of anther cracking inferior to ‘Qx-097’, pollen residue remains after pollen dispersing;

  

‘Qx-115’: anther non-cracking, non-dispersal of pollen.