M.B. Jackson - Böcker

Proceedings of the 14th Long Ashton International Symposium: Plant Roots - From Cells to Systems held in Bristol, UK, 13-15 September 1995

The formation of roots is in some respects one of the least fundamentally understood of all plant functions. Propagation by cuttings is the aspect that will occur first to most gardeners and horticulturists, and it is certainly the most useful application. But any observant traveller in the tropics can notice that some trees have the habit of forming roots in the air. Climbers like Cissus bear long fine strings of roots hanging down. Pandanus trees tend to have stout aerial roots issuing from the bases of the long branches, while the tangle of roots around the trunk of many of the Ficus species is characteristic. In Ficus bengalensis, in particular, stout cylindrical roots firmly embedded in the ground from a height of 3 to 5 meters give support to the long horizontal branches, enabling them to spread still further. In the big old specimen at Adyar near Madras, the spread of these branches all around the tree, each with a strong root growing out every few meters, makes a shaded area under which meetings of almost 5000 people are sometimes held. The history of how the formation of roots on stem cuttings was found to be under hormonal control is worth repeating here.

tests the suitability of using mannitol as an osmoticum during experiments. Pressure probe and SiCSA techniques The expanding maize root tip Use of the cell pressure probe (Htisken et aI. , 1978) and single-cell sampling and analysis (SiCSA; Tomos Individual cells expand to many times their ongl- et aI. , 1994) provide an approach to study plant water nal length as they progress from the meristem to the and solute relations at the resolution of the individual mature zone of root tips. The expansion first accel- cell. In the case of water relations, the pressure probe erates and then decelerates, stopping at the proximal provides the only technique that measures cell tur- end of the expansion zone (Pritchard, 1994). This is gor pressure, and hence turgor adjustment processes, accomplished at constant ceJl turgor (P) and with a loss directly. In some cases, such as the motor cells of pul- of osmotic (7l'j) pressure in the order of 15% (wheat: vini or in the stomatal complex, turgor varies between Tomos et aI. , 1989; maize: Pritchard et aI. , 1993; adjacent cells - making analysis at single cell resolu- Pritchard and Tomos, 1993).The constant turgor indi- tion essential for understanding mechanisms (Irving et cates that changes in cell-wall mechanical properties, aI. , 1994). Correlating turgor pressure measurements rather than driving force, are responsible for the imme- with cell expansion rate permits unique measurement diate control of expansion-rate in roots (Pritchard et aI.