Ingrid Tichá

Photosynthesis of plant régénérants. Specificity ofin vitro conditions and plantlet response

Regenerants from tobacco(Nicotiana tabacum L. cv. White Burley) leaf segments cultivatedin vitro in vessels with solid agar medium under usual conditions (plantlets) grew under very low irradiance (I = 40 μxmol m−2 s−1), very high relative humidity (more than 90%) and decreased CO2 concentration (ca) during light period. In comparison with seedlings of a similar number of leaves and similar total leaf area grown in sand and nutrient solution, the plantlets had lower dry mass of shoots and roots per plant and thinner leaves almost without trichomes and epicuticular waxes. Due to a low transpiration rate under high relative humidity the water potential of plantlet leaves was higher than that of seedling leaves and the difference in water potential between leaves and medium was lowei. The rate of water loss from leaves detached from plantlets was considerably faster than that from seedlings under the same conditions (I = 110 μrnol m−2; s−1, temperature 30 °C, relative humidity 50 %). Net photosynthetie rates (Pn) of leaves of plantlets and seedlings measured under saturating I, natural ca and the leaf temperature 20 °C were similar, nevertheless the shape of curves relating Pn to c» indicated some differences in photosynthetie parameters(e.g. saturation of Pn under lower ca> higher CO2 compensation concentration in plantlets than in seedlings). Similarly compensation and saturating I were lower in plantlets than in seedlings. The shape of transpiration curves as well as the expressive linear phases of PN(ca) and PN(I) curves of plantlet leaves indicated ineffective stomatal control of gas exchance. These results were confirmed by microscopic observations of stomatal movementsin situ

A closed system for measurement of photosynthesis, photorespiration and transpiration rates

An installation is described enabling measurements of photosynthesis, transpiration and dark respiration, and estimation of photorespiration rates at different carbon dioxide and oxygen concentrations, at different irradiances and leaf temperatures.AbstractV práci je podrobně popsáno zařízení, které umožňuje měření rychlosti fotosynthesy, transpirace a temnotního dýchání a výpočet rychlosti fotorespirace při různých koncentracích kysličníku uhličitého a kyslíku, při různém ozáření listu a různé jeho teplotě.

Integration of Fhotosynthetic Characteristics during Leaf Development

The formation of leaf structure, the development of the chloroplast as a basic unit of photosynthesis, the synthesis of pigment complexes and the components of the electron transport chain in the thylakoid as the place of the photochemical reactions of photosynthesis have been touched on or thoroughly analysed by many authors. Unfortunately, the major part of the existing literature contains the determination of usually only one or two characteristics which belong to the complex mosaic called “the photosynthetie apparatus”. These findings have already been described in the previous Chapters. The papers with a more synthetic aspect are as rare as those that thoroughly analyse the whole leaf life span or the complete leaf insertion gradient.

An installation for measuring carbon dioxide and water vapour exchange rates with a precise environmental control

An open system has been designed which enables a simple and rapid manual regulation of the CO2 concentration and absolute humidity in the assimilation chamber according to the actual CO2 and water vapour exchange rates, respectively. This ensures a constant effective CO2 concentration and humidity irrespective of the gas exchange of the leaves. The installation is supplemented with an irradiation system providing irradiance at the leaf level up to 3 200 μeinstein m−2s−1 (400–700 nm),i. e. ca. 675 W m−2.

Conductances for Carbon Dioxide Transfer in the Leaf

Carbon dioxide passes on the pathway from the atmosphere to the carboxylation sites in chloroplasts through a series of structures differing in physical, chemical and biological properties which more or less control its flow rate.

Carbon dioxide exchange in primary bean leaves as affected by water stress

Net photosynthetic rate decreased sharply to zero in the range of water potential- 8.0 to -10.4 x 105 Pa. The observed decrease in photosynthetic rate was due not only to the decrease in epidermal conductance, but also to the decrease in intraoellular conductance. Both conductances decreased in the same range of water potential. With decreasing water potential photorespiration rate decreased whereas dark respiration rate remained rather unchanged. Simultaneously CO2 compensation concentration increased. These facts constitute an indirect evidence that water stress inhibited not only transport of CO2 from atmosphere to carboxylation sites in chloroplasts, but also its conversion into photosynthates.

CO2 compensation concentration in bean Leaves: Effect of photon flux density and leaf age

Carbon dioxide compensation concentration,Г, net photosynthetic rate,Pn, and photorespiration rate,Rl, were measured in young, adult and old primary leaves ofPhaseolus vulgaris L. over a range of photon flux densities using a closed system with IRGA. Irrespective of leaf age,Г decreased rapidly with rising photon flux density up toca. 260 (μmol m−2 s−1. From this valueГ did not change with photon flux density under constant temperature, reaching on the average 178, 118 and 239 mg m−3 in young, adult and old leaves, respectively. Changes with age in curves relatingPn andRl to photon flux density were found.

Relationship between intracellular resistance for net CO2 uptake rate and phosphoenolpyruvate carboxylase activity in leaves of Zea mays L.

Summary In leaves of Zea mays L. the intracellular resistance r i was calculated as the reciprocal value of the initial slope of the curve for the relationship between net CO 2 uptake rate and intercellular CO 2 concentration. In extracts from the same leaves the maximum rate of phosphoenolpyruvate (PEP) carboxylation V P was determined in vitro . A significant linear correlation between r i and the reciprocal value of V P was obtained. From this correlation a value of the Michaelis constant of PEP carboxylase for CO 2 in vivo of 250 mg m −3 (in the gas phase) and a constant resistance component of about 90 sm −1 were derived. This result is interpreted as an indication that processes of CO 2 transfer within the mesophyll cells may be an important limiting factor for overall CO 2 fixation in C 4 plants.

Contribution of leaves of different ages to plant carbon balance as affected by potassium supply and water stress

The carbon balances of whole, 21-d old French bean plants (Phaseolus vulgaris L.) grown in standard nutrient solution (1K) and its modifications without (OK) or surplus (2K) potassium were calculated from the daily photosynthetic carbon inputs of individual leaves, and the daily respiratory carbon losses by individual leaves, stalks and petioles, and roots. Under the three K concentrations, maximum net photosynthetic rates (Pn) were found in the 2nd or in the 3rd trifoliate leaves, maximum respiratory rates (Rd) in the youngest, 4th trifoliate leaves; the Pn/Rd ratio decreased with leaf age. In all leaves of 2K plants, leaf dry masses and thicknesses, Pn, Pn/Pd ratios, and stomatal and intracellular conductances were lower than in OK and IK plants. Daily whole-plant net carbon gain was highest in IK plants, whereas in OK and 2K plants it was 98.0 and 81.3 % of IK, respectively. Similar values were found in the parameters of growth analysis, namely in net assimilation rates and relative growth rates.No differences were found in water potential (Ψw) or water saturation deficit (Wsat) in the OK, 1K and 2K plants sufficiently supplied with water or during wilting and resaturation. The decrease in Ψw to −0.97 MPa was associated with a 19.9 %, 31.4 % and 23.4 % decrease in Pn of OK, 1K and 2K plants, respectively, but no effect on Rd was found. In the three variants, the short-time effect of mild water stress was fully reversible.

Carbon Dioxide Transfer and Photochemical Activities as Factors of Photosynthesis during Ontogenesis of Primary Bean Leaves

The maximum photosynthetic rate which can be attained by plants under optimum conditions is limited in principle by two genetically controlled factors, i.e. by the maximum activity of the photochemical systems and by the maximum conductance of leaf tissues for carbon dioxide transfer from ambient air to carboxylation sites. Both the physical, CO2 transfer part and the biochemical, energy conversion part of photosynthesis (see schemes on Figs. 1 and 2) are composed of several catenary segments. The activity of each individual segment changes in varying degree during the development of a leaf and a plant, resulting finally in ontogenetic changes of net CO2 influx or dry matter increment. The changes in these generally used measures of photosynthetic rate are often reported in the literature (for review see SESTAk & CATSKÝ 1967).