Involvement of phytochrome in regulation of transpiration: red-/far red-induced responses in the chlorophyll-deficient mutant of pea

Transpiration rhythmicity and intensity were investigated in the chlorophyll-deficient mutant XL18 of Pisum sativum L. and in the phytochrome-deficient mutant aurea of Lycopersicon esculentum Mill. A custom-built psychrometer was used. In the XL18 mutant an acute transpiration response to monochromatic irradiation was observed such that red (R) light increased and far-red (FR) decreased transpiration rate, with equal rates of change. This result indicates that phytochrome is involved in regulation of transpiration. In wild type pea the chlorophyll-dependent component of transpiration was also shown to involve phytochrome. Monochromatic irradiation by red or far-red light induced an increase in transpiration with acceleration dependent on time of day. The response was irreversible by light of either wavelength. We conclude that both photoreceptors are involved in the acute response. Investigation of the daily course of transpiration revealed rhythmic changes in wild type pea and tomato under natural light conditions and in constant darkness. The rhythm was not apparent in the XL18 mutant in constant darkness, or in the aurea mutant under natural illumination. The latter results show that phytochrome, as a photoreceptor, is essential for maintaining the rhythm upon irradiation, while the photosynthetic component is crucial in darkness.

Consequences of High CO2-Concentrations in Air on Growth and Gas-Exchange Rates in Tobacco Mutants

Wild type tobacco N. tabacum var. John William’s Broadleaf and the tobacco aurea mutant Su/su were permanently grown under 700 ppm CO2 in air. In comparison to plants grown under 350 ppm CO2 in air but under otherwise identical conditions growth was substantially enhanced. Gas exchange measurements carried out by mass spectrometry show that the rate of photosynthesis in the wild type and in the mutant is increased by more than 100%. The photorespiratory rate in the wild type measured as 18O2-uptake in the light in the “700 ppm CO2-plants” is not reduced to the extent expected or deduced from experiments in which the 350 ppm system responds under in vitro conditions to 700 ppm CO2. An analysis of the induction kinetics of room temperature fluorescence kinetics of the adapted (700 ppm CO2) system and the control system (350 ppm CO2) under various CO2-partial pressures shows that permanent growth under the elevated CO2-partial pressure leads to a structural modification of the photosynthetic apparatus.