| Abstract: | Phaseolus seedlings were grown in liquid culture under controlledtemperature and irradiance and measurements were made of dailyvariation in growth of the first trifoliate leaves. Leaf growthrate was significantly enhanced within a few hours of the startof the light period. Over a similar time, a small decrease inleaf turgor and an increase in cell wall plasticity were recorded.Slowly declining growth rates as the light period progressedmay have been caused by decreases in turgor during this time.When water availability to the leaves was restricted by growingthe plants for several days in nutrient solution maintainedat a low temperature (12°C), the daily pattern of growthof the trifoliates was changed quite markedly. Dark-growth rateswere slightly enhanced, while light-growth rates were significantlyreduced when compared to growth rates of plants well-suppliedwith water (roots at 20°C). Relative ‘plateau’growth rates of plants well-supplied (ww) with water or sufferinga restricted supply (ws) in the light (L) and in the dark (D)were as follows: ww L > ws D > ww D > ws L. In thelight, turgors of the two groups of plants were similar, suggestingthat the reduced growth rate of the cooled plants resulted froma change in cell wall structure and/or properties. Immediatelybefore the lights were switched on, plants grown with a restrictedwater supply showed relatively high turgors in the trifoliatesand these were presumably responsible for the enhanced growthrates at this time. Restriction of water availability may haveslightly increased the plasticity of cell walls and decreasedthe yield threshold for growth. The control of leaf growth inplants developing water deficit is discussed. Key words: Leaf growth turgor, Cell wall plasticity, Water deficit, Light |
