LIGHT ADAPTATION OF PHOTOSYNTHETIC APPARATUS IN AJUGA-REPTANS L., A SHADE-TOLERANT PLANT AS AN EXAMPLE

Characteristics of the photosynthetic apparatus of Ajuga reptans L, pl ants grown under a forest canopy and in an open plot were examined. Sh aded plants had leaves with lower weight per unit leaf area (2.5-fold reduction) and 1.3 times higher chlorophyll content. The chlorophyll a : b ratio varied within the limits of 2.2-2.8 and 2.5-3.2, with light -harvesting complexes comprising 57-69 and 53-62% of the total chlorop hyll, respectively. Leaves did not markedly differ in their maximum ph otosynthetic rates (3-5 mg CO2/(dm(2) h)) and photosynthetic rates at the intensity of radiation of adaptation (IRA) (1.8 mg CO2/(dm(2)/h)). The IRA (5-10 W/m(2)) and light compensation point (1-3 W/m(2)) were significantly lower in shaded plants. On the whole, morphological and physiological characteristics of the photosynthetic apparatus varied w ithin a rather narrow range, which characterizes Ajuga reptans as a sh ade-tolerant plant. It is concluded that shade tolerance is a heredita ry trait, and that plant viability under shade conditions slightly cor relates with its ability to achieve high photosynthetic rates in light .