Poikilohydry and homoihydry: antithesis or spectrum of possibilities?

Abstract

SummaryPlants have followed two principal (and contrasting) strategies of adaptation to the irregular supply of water on land, which are closely bound up with scale. Vascular plants evolved internal transport from the soil to the leafy canopy (but their 'homoihydry' is far from absolute, and some are desiccation tolerant (DT)). Bryophytes depended on desiccation tolerance, suspending metabolism when water was not available; their cells are generally either fully turgid or desiccated. Desiccation tolerance requires preservation intact through drying-re-wetting cycles of essential cell components and their functional relationships, and controlled cessation and restarting of metabolism. In many bryophytes and some vascular plants tolerance is essentially constitutive. In other vascular plants (particularly poikilochlorophyllous species) and some bryophytes tolerance is induced by water stress. Desiccation tolerance is adaptively optimal on hard substrates impenetrable to roots, and on poor dry soils in seasonally dry climates. DT vascular plants are commonest in warm semiarid climates; DT mosses and lichens occur from tropical to polar regions. DT plants vary widely in their inertia to changing water content. Some mosses and lichens dry out and recover within an hour or less; vascular species typically respond on a time scale of one to a few days.© New Phytologist (2002) 156 :

To concentrate or ventilate? Carbon acquisition, isotope discrimination and physiological ecology of early land plant life forms

“…Additionally, the highest overall WUE found for M. polymorpha was also consistent with such a narrow range of TWC to support maximal assimilation and ETR (figure 2; see discussion below; Proctor & Tuba 2002).…”

Exploring the Mechanism of Physcomitrella patens Desiccation Tolerance through a Proteomic Strategy

“…In the dried state, plants of the former type retain their chloroplast structure whereas plants of the latter break them down (Proctor and Tuba, 2002). P. patens belongs to the homoiochlorophyllous group: chlorophyll levels remained high and chloroplast structure was largely preserved, although it was changed to a spherical form with less well-stacked thylakoids.…”

Water Transport by Aquaporins in the Extant Plant Physcomitrella patens

“…According to Proctor and Tuba (2002), poikilohydry is not the primitive starting point leading to homoio- Opening AQPs adds a pathway to water across the membrane, but does not modify the magnitude of the transpiration flow (right drawing). mb, Membrane; cw, cell wall; bl, boundary layer; dotted arrow, flow through the lipid bilayer; white arrow, flow through AQPs.…”

“…Gametophore leaves gain or loose water depending on the relative humidity (RH) in the air measured far from the leaves (Nobel, 1999). Water is mainly drawn in by the leaves from external reservoirs through capillary action (Proctor and Tuba, 2002). It is lost through the aerial parts of the plant when RH decreases in the air near the cell wall.…”