Physiological Aspects of Sugar Exchange between the Gametophyte and the Sporophyte of Polytrichum formosum

Abstract

The sporophyte of bryophytes is dependent on the gametophyte for its carbon nutrition. This is especially true of the sporophytes of Polytrichum species, and it was generally thought that sucrose was the main form of sugar for long distance transport in the leptom. In Polytrichum formosum, sucrose was the main soluble sugar of the sporophyte and gametophyte tissues, and the highest concentration (about 230 mM) was found in the haustorium. In contrast, sugars collected from the vaginula apoplast were mainly hexoses, with traces of sucrose and trehalose. p-Chloromercuribenzene sulfonate, a nonpermeant inhibitor of the cell wall invertase, strongly reduced the hexose to sucrose ratio. The highest cell wall invertase activity (pH 4.5) was located in the vaginula, whereas the highest activity of a soluble invertase (pH 7.0) was found in both the vaginula and the haustorium. Glucose uptake was carriermediated but only weakly dependent on the external pH and the transmembrane electrical gradient, in contrast to amino acid uptake (S. Renault, C. Despeghel-Caussin, J.L. Bonnemain, S. Delrot [1989] Plant Physiol 90: 913-920). Furthermore, addition of 5 or 50 mm glucose to the incubation medium induced a marginal depolarization of the transmembrane potential difference of the transfer cells and had no effect on the pH of this medium. Glucose was converted to sucrose after its absorption into the haustorium. These results demonstrate the noncontinuity of sucrose at the gametophyte/sporophyte interface. They suggest that its conversion to glucose and fructose at this interface, and the subsequent reconversion to sucrose after hexose absorption by haustorium cells, mainly governs sugar accumulation in this latter organ.

Sugar uptake by the dermal transfer cells of developing cotyledons of Vicia faba L.

“…These values contrast with a Km of 47 mM for glucose uptake by the haustorial transfer cells of Polytrichum sporophytes (Renault et al 1992). However, in the latter case, the linear concentration dependence of 3-O-methyl glucose (Renault et al 1992) suggests the high Km may reflect the kinetics of glucose metabolism rather than membrane transport.…”

“…Significantly, the Km derived for the Vicia transfer cells is comparable to that estimated for the putative sucrose porter of minor-vein transfer cells of pea leaves (Wimmers and Turgeon 1991). These values contrast with a Km of 47 mM for glucose uptake by the haustorial transfer cells of Polytrichum sporophytes (Renault et al 1992). However, in the latter case, the linear concentration dependence of 3-O-methyl glucose (Renault et al 1992) suggests the high Km may reflect the kinetics of glucose metabolism rather than membrane transport.…”

“…Renault et al 1989Renault et al , 1992. The results of these investigations provide evidence for energy-dependent mediated solute uptake.…”

The MADS-domain protein PPM2 preferentially occurs in gametangia and sporophytes of the moss Physcomitrella patens

“…The function of the sporophyte foot in energy supply is even more obvious. In mosses, the diploid generation completely depends on nutrition by the dominant gametophyte (Browning and Gunning, 1979a,b;Renault et al, 1992). A high expression of PPM2 in the aforementioned tissues of P. patens may therefore be involved in the definition of sink tissues to ensure proper development of those organs that are required for the transition into the next generation of the life cycle.…”

Ultimate Costs of Sporophyte Production in the Clonal Moss Hylocomium splendens

“…Notably most bryophytes lack belowground structures that allow a more flexible use of energy and nutrients. Furthermore, costs of bryophyte sexual reproduction are not likely to be offset by photosynthesis of reproductive structures (Proctor 1977, Renault et al 1992. Nevertheless, while costs of sexual reproduction have been demonstrated for many vascular plants, problems with nondestructive identification of the tiny ''individuals'' (Rydgren and Økland 2002a) have hampered studies of bryophytes .…”