Stomatal and photosynthetic responses ofCichorium intybus leaves to sulfur dioxide treatment at different stages of plant development

Abstract

Fifty-day-oldCichorium intybus Linn, plants were exposed to 1 ppm sulfur dioxide gas, 2 h per day for 7 consecutive days. Their leaves as well as those from the control plants were sampled at pre-flowering, flowering, and post-flowering stages to study their morphological, physiological, and biochemical responses to SO₂ stress. The number, dimensions, area, and biomass of leaves were less in the treated plants. Length and width of stomatal apertures on both epidermises were greater for leaves exposed to SO₂. The Stomata were longer on the adaxial epidermis, but shorter on the abaxial epidermis, except at the pre-flowering stage. Stomatal widths varied widely. Compared with the controls, the abaxial epidermis on treated leaves showed consistently lower stomatal densities as well as stomatal indices. This was also true for the adaxial epidermis during the post-flowering stage. The photosynthetic rate and stomatal conductance were reduced in the SO₂-exposed plants, but intercellular CO₂ concentrations increased at the pre-flowering stage and, subsequently, declined. Chlorophyll a, carotenoid, and total chlorophyll contents increased at the pre-flowering stage, and then decreased. The level of chlorophyllb was reduced throughout plant development compared with the untreated controls.