Water ascent in trees and lianas: the cohesion-tension theory revisited in the wake of Otto Renner

The cohesion-tension theory of water ascent (C-T) has been challenged over the past decades by a large body of experimental evidence obtained by means of several minimum or non-invasive techniques. The evidence strongly suggests that land plants acquire water through interplay of several mechanisms covered by the multi-force theory of (U. Zimmermann et al. New Phytologist 162: 575615, 2004). The diversity of mechanisms includes, for instance, water acquisition by inverse transpiration and thermodynamically uphill transmembrane water secretion by cation-chloride cotransporters (L.H. Wegner, Progress in Botany 76:109141, 2014). This whole plant perspective was opened by Otto Renner at the beginning of the last century who supported experimentally the strictly xylem-bound C-T mechanism, yet anticipated that the water ascent involves both the xylem conduit and parenchyma tissues. The survey also illustrates the known paradigm that new techniques generate new insights, as well as a paradigm experienced by Max Planck that a new scientific idea is not welcomed by the community instantly

Amine Transport in Riccia fluitans: Cytoplasmic and Vacuolar pH Recorded by a pH-Sensitive Microelectrode

The cytoplasmic and vacuolar pH and changes thereof in the presence of ammonia (NH(4)Cl) and methylamine (CH(3)NH(3)Cl) have been measured in rhizoid cells of Riccia fluitans by means of a pH-sensitive microelectrode. On addition of 1 micromolar NH(4)Cl, the cytoplasmic pH of 7.2 to 7.4 drops by 0.1 to 0.2 pH units, but shifts to pH 7.8 in the presence of 50 micromolar NH(4)Cl or 500 micromolar CH(3)NH(3)Cl. The pH of the vacuole increases drastically from 4.5 to 5.7 with these latter concentrations. Since a NH(4)(+)/CH(3)NH(3)(+) uniporter has been demonstrated in the plasmalemma of R. fluitans previously (Felle 1983 Biochim Biophys Acta 602:181-195), the concentration-dependent shifts of cytoplasmic pH are interpreted as results of two processes: first, acidification through deprotonation of the actively transported NH(4)(+); and second, alkalinization through protonation of NH(3) which is taken up to a significant extent from high external concentrations. Furthermore, it is concluded that the determination of intracellular pH by means of methylamine distribution is not a reliable method for eucaryotic systems