Jarmila Solárová

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

Changes in minimal diffusive resistances of leaf epidermes during ageing of primary leaves of phaseolus vulgaris L.

Minimal diffusive resistances of both leaf epidermes increased during normal and retarded ageing (moving secondary leaves aside, plant decapitation). The retarded ageing of primary leaves slowed down increase in epidermal resistance (rep), and was also reflected in the prolongation of their growth, increase of leaf area, size of epidermal and guard cells and stomatal pores. Decrease of stomata density was to some extent balanced by an increase in the pore size; the later rapid rise in diffusion resistance was induced by the loss of stomata ability to open fully.

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.

Stomata Reactivity in Leaves at Different Insertion Level During Wilting

The influence of the external environment as a primary factor on the movement of stomata has been the subject of many papers by different authors. Much less attention has been paid to the effect of internal factors, i.e. the genotypes of plants, their development and growth. The conditions of the environment have an indirect effect in this case through the plant organism, certain qualities of which are determined by them.

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.

Leaf conductance and gas exchange through adaxial and abaxial surfaces in water stressed primary bean leaves

Epidermal conductances for water vapour transfer(gep), water vapour efflux(E), and net photosynthetic CO2 uptake (PN) through adaxial and abaxial leaf surfaces were estimated, simultaneously during the development of water stress in primary leaves ofPhaseolus vulgaris L. Hydration level was characterized by water saturation deficit (ΔWsat), water potential (Τw), osmotic potential (Τ8) and pressure potential (Τp). The conductance of the abaxial epidermis was consistently greater than that of the adaxial epidermis, but the response of both surfaces to the increase in water stress corresponded: with increasing water stress epidermal conductances slightly increased, reached a plateau and then sharply decreased (at a rate of about 1.10x10-6 cm s-1 Pa-1 and 1.55x10-6 cm s-1 Pa-1 of Τw for adaxial and abaxial epidemics, respectively) to very low value. The curves expressing relationship between epidermal conductances and Δ Wsat, Τw, Τs, as well as Τp were of a similar character. E and PN through adaxial and abaxial surfaces were practically not affected until water stress reached the “critical” value (Τw from — 8.2 to — 9.2 x 105 Pa). With further increase in water deficit, however, they sharply decreased. The “critical” value of Τw was the same for both leaf surfaces.

Hydroreactivity of stomata in kale leaves of different insertion level as determined by analysis of transpiration curves

Values of the water saturation deficit (WSD) for hydroactive stomatal movements of kale leaves were estimated using the method of transpiration curve analysis.Stomata of young leaves started closing at WSD values of 5 to 6 per cent and were completely closed at 18 to 20 per cent WSD. During maturation and ageing of leaves these WSD values increased to 12.5 and 18 to 23 per cent respectively. Thus the stomatal reaction is more sensitive to changes in WSD in adult leaves than in young ones. After maturation is attained both values decrease. In apparently withering leaves the individual phases of transpiration curves can barely be distinguished, probably for the reason that even under optimal conditions their stomata remain half-closed and at high WSD values an incomplete closing of the aperture occurs. The injured cuticle of withering leaves affects the shape of the transpiration curve as well.AbstractHodnoty vodního sytostního deficitu (VSD) kritické pro hydroaktivní pohyby průduchů krmné kapusty byly zjišťovány analýzou transpiračních křivek.Průduchy mladých listů se začínaly uzavírat při hodnotách VSD 5–6 % a zcela se uzavíraly při 18–20% VSD. Během dospívání a stárnutí listů se tyto hodnoty VSD zvyšovaly až na 12,5, případně 18–23% VSD. U dospělých listů je stomatární reakce citlivější na změny VSD než u listů mladých. Po dosažení dospělosti se obě hodnoty VSD snižují. U listů zřetelně odumírajících lze jen velmi obtížně rozlišit jednotlivé fáze transpiračních křivek pravděpodobně proto, že jejich průduchy zůstávají i za optimálních podmínek přivřeny a naopak při vysokých hodnotách VSD nedochází k úplnému utěsnění štěrbiny. Také porušená kutikula u starých listů má vliv na tvar grafického vyjádření transpirační křivky.

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.

Ontogenetic changes in response of adaxial and abaxial epidermal conductances to water stress

The sensitivity of stomata to water stress increased during ontogeny of primary bean leaves growing under constant environmental conditions: the decrease in both adaxial and abaxial epidermal conductances was induced by slightly more negative values of leaf water potential in young than in mature and especially old leaves. However, these differences were less expressive than the differences mentioned in the literature for leaves of different insertion level, where adaptations to microclimatic conditions in different canopy layers in addition to ontogeny may occur.