Anther dehiscence in Lycopersicon esculentum Mill. I. Structural aspects

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SUMMARY

The structure and chemistry of anther dehiscence in Lycopersicon esculentum (Solanaceae) has been examined using a range of microscopic techniques. No Single event or process has been identified as being solely responsible for the release of the pollen grains, instead, an integrated programme of development across a number of tissues appears to be involved. The earliest events in this process are changes in the intersporangial septa and growth of specific epidermal cells. Large numbers of calcium oxalate (druse) crystals accumulate in the septa and may play a part in the weakening and eventual enzymic dissolution of this cell layer. The differential growth of epidermal cells fulfils two roles; firstly it serves to define the point of rupture or stomium and, secondly the enlarged cells generate and transmit the force required to disrupt the unenlarged stomial cells. Adjacent loculi are unified within the anther first by the enzymic degradation of the crystal-filled septal cells, which is followed by similar degradation of the remaining connective tissue cells and the eventual rupture of the remnants of the tapetal walls.

Once the epidermal cell system has been established, and adjacent loculi unified, the endothecium develops in the anther wall, but only in the region adjacent to the stomium in the distal third of the anther. Opening of the anther is achieved by a combination of the mechanical forces generated by tile enlarged epidermal, and possibly the endothecial, cells operating on the previously weakened stomial cells, which at the time of rupture have started to desiccate. Following rupture of the anther wall, the stomium is transformed from a slit to a wide-mouthed pore via the ordered desiccation and contraction of the endothecial and surrounding tissue. Although these final stages of dehiscence show some sensitivity to ambient vapour pressure differences, there is little doubt that the process of dehiscence is not purely a desiccatory one, indeed only specific localised areas of the anther degenerate and dehydrate, whilst the bulk of the anther tissue remains turgid and metabolically active.

This multicomponential type of anther dehiscence is discussed in the perspective of other models proposed to explain anther opening in members of the Solanaceae, as well as systems suggested for other plants which clearly possess very different methods of dehiscence.

Ancillary