Assessment of Photosynthesis and Transpiration in Hordeum Vulgare L. Seedlings of Different Ages Under Heat Stress Using Infrared Spectroscopy

Abstract

The rate of photosynthesis and transpiration in 4-, 7- and 11-day-old Hordeum vulgare L. seedlings exposed to high temperature was studied using infrared spectroscopy. To analyse the mechanisms underlying their regulation the state of the stomata and the real temperature of the primary leaf of these seedlings were assessed. It was found that heat treatment (40^oC, 3 h, illumination 120 µmol quanta · m^–2 · s^–1) did not affect net photosynthesis and stomatal conductivity in young 4-day-old Hordeum vulgare L. seedlings at the effective cools of the leaf due to activation of transpiration. In the primary leaf fully formed by the age of 7 days, after heat treatment, neither the stomatal conductance nor the transpiration rate changed, and the leaf cooled to a lesser than in 4-day-old seedlings, and net photosynthesis was suppressed. In the aging 11-day-old leaf under heat stress, the conductivity of the stomata for both water vapour and CO₂ decreased, which caused the suppression of transpiration and photosynthetic activity and significant heating of the leaf. We concluded about the different response of the stomata and transpiration to heat in Hordeum vulgare L. seedlings of different ages, aimed at maintaining the most effective balance between cooling the leaf and maintaining the water potential of plants.