Decrease In Photon Flux Density Research Articles

Ex Vitro Phenotype Stability is Affected by In Vitro Cultivation

Plant phenotype stability during ex vitro growth, one of the main requirements of plant micropropagation, was tested on tobacco. Plants cultivated in vitro in the presence of 3 % sucrose under photon flux density (PFD) of 200 μmol m-2 s-1 (3 % HL plants) showed the best growth and photosynthetic parameters in the course of 7-day acclimation. However, significant change in phenotype of these plants appeared under a decrease in PFD to 50 μmol m-2 s-1 during further ex vitro growth (in the period of 7th - 17th day). Much higher internodia elongation was found in 3 % HL plants in comparison with plants grown in vitro on sucrose media under PFD of 50 μmol m-2 s-1 (3 % LL) or without sucrose either under PFD of 50 μmol m-2 s-1 or 200 μmol m-2 s-1 (0 % LL, 0 % HL). It can be presumed that 3 % HL plants show permanent demand for high PFD. Neither ABA or chlorophyll contents nor de novo thylakoid membrane synthesis were related to the morphogenic effect of low PFD. Changeable contents of hexoses in leaves of 3 % HL and 3 % LL plants were in no direct correlation to the elongated growth.

Effects of leaf age, nitrogen nutrition and photon flux density on the organization of the photosynthetic apparatus in leaves of a vine (Ipomoea tricolor Cav.) grown horizontally to avoid mutual shading of leaves

Effects of leaf age, nitrogen nutrition and photon flux density (PFD) on the organization of the photosynthetic apparatus in leaves were investigated in a vine, Ipomoea tricolor Cav., which was grown horizontally so as to avoid mutual shading of leaves. The plants were grown hydroponically at two nitrate levels under two growth light treatments. For one group of the plants, leaves were exposed to full sunlight. For another group, respective leaves were artificially shaded in a manner that simulated changes in the light gradient with the development of an erect herbaceous canopy: old leaves were placed under progressively shadier conditions with growth of the plants (canopy-type shading). In all the treatments, chlorophyll (Chl) content gradually decreased with leaf age. Photosystem I (PSI) per Chl was constant, independent of leaf age, nitrogen nutrition and/or PFD. Photosystem II (PSII) and cytochrome / per Chl, and Chl a/b ratio were independent of leaf age and/or nitrogen nutrition but decreased with the decrease in growth PFD. Ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39, RuBPCase) per Chl steeply decreased with decrease in PFD. When leaves grown at the same PFD were compared, RuBPCase/Chl was lower in the plants grown under lower nitrogen availability and also decreased with leaf age in the plants grown without shading. These decreases were attributed to the curvilinear relationship between RuBPCase and Chl in leaves grown at full sunlight, that was independent of nitrogen availability and leaf age. From these results, it is concluded that the composition of the photosynthetic apparatus is independent of leaf age but changes depending on the light environment and total amount of photosynthetic components of the leaf.

Variation Among Populations of Prunella vulgaris L. in Plastic Responses to Light

Phenotypic responses to photon flux density (PFD) by five populations of the herbace- ous perennial Prunella vulgaris L. were compared. Plants from each population were grown in two light environments, and we measured the effect of PFD on overall performance (size) as well as the responses of several physiological traits to PFD. Both measures of size and physiological traits differed significantly between light environments and among populations. Significant population- by-environment interaction was detected for measures of size but not for any physiological traits. These results indicate significant differ- ences among populations in the extent to which size is reduced by a decrease in PFD. However, these differences are not the result of variation in the responses of the physiological traits we measured. A comparison of the patterns of correlations among traits in the two light environments indi- cated signficant similarity of correlation structure between environments. This result contrasts with those of studies showing strong environmental dependence of phenotypic relationships between traits. Key-words: Phenotypic plasticity, physiological responses to light, population-by-environment interac- tions, population variation, Prunella vulgaris, trait correlations

Analysis of the control of photosynthesis in C 4 plants by changes in light and carbon dioxide

Parallel measurements of contents of photosynthetic intermediates, activities of enzymes of photosynthetic carbon assimilation, gas-exchange rates and components of chlorophyll-fluorescence quenching in leaves of C 4 plants are considered in relation to changes in photon flux density (PFD) and CO 2 . The influence of varying light and CO 2 concentration upon changes in the amounts of phosphoenolpyruvate (PEP) in leaves of C 4 plants during steady-state photosynthesis are interpreted in terms of the regulatory properties of PEP carboxylase and in terms of feedback interactions between the Calvin cycle and the C 4 cycle. Relations between electron transport and carbon assimilation are discussed in terms of the regulation of the supply of ATP and NADPH and the demands of carbon assimilation. In low light these relations differ in C 3 and C 4 plants. The lag in photosynthetic carbon assimilation in maize that follows a decrease in PFD has been analysed. The changes that occur in enzyme activities, metabolites and components of chlorophyll-fluorescence quenching following the transition from high to low light indicate that diminished production of ATP and NADPH is responsible for the lag in photosynthetic carbon assimilation and may reflect a stimulation of cyclic electron flow to make up a deficit in ATP.

Regulation of photosynthesis in leaves of C 4 plants following a transition from high to low light

The aim of this work was to investigate the factors whichregulate photosynthetic carbon assimilation in leaves of maize ( Zea mays ) and Amaranthus edulis following a decrease in photon flux density. The principal observations in maize were that, after a decrease in photon flux density; (i) there was a transient inhibition of the rate of carbon assimilation; (ii) the pool of phosphor enol pyruvate rose while the flux decreased, indicating rapid regulation of the activity of phosphor enol pymvate carboxylase; (iii)the triose- P /glycerate-3- P ratio declined drastically; at the same time the pool of pyruvate increased several-fold; (iv) the activation state of NADP + -malate dehydrogenase declined rapidly, whilethe activation states of pyruvate, P i dikinase, fructose-1,6-bisphosphatase and sucrose phosphate synthase changed relatively slowly; (v) therewas a rapid decrease in non-photochemical quenching of chlorophyll fluorescence and a rapid oxidation and re-reduction of Q A followed by a slow oxidation of Q A ; (vi) in A. edulis the content of aspartate and of the total pool of C 4 -cycleintermediates increased. The observations are discussed in terms of the regulation of C 4 photosynthesis and in terms of the supply of, and demand for, the products of electron transport by carbon metabolism. It is suggested that the transient inhibition of photosynthetic carbon assimilation in maizeleaves is accompanied by a high demand for ATP which is met by cyclic electron transport

Regulation of Ribulose-1,5-Bisphosphate Carboxylase Activity in Alocasia macrorrhiza in Response to Step Changes in Irradiance

The regulation of ribulose-1,5-bisphosphate (RuBP) carboxylase (Rubisco) activity and pool sizes of RuBP and P-glycerate were examined in the tropical understory species Alocasia macrorrhiza following step changes in photon flux density (PFD). Previous gas exchange analysis of this species following a step increase in PFD from 10 to 500 micromoles quanta per square meter per second suggested that the increase in photosynthetic rate was limited by the rate of increase of Rubisco activity for the first 5 to 10 minutes. We demonstrate here that the increase in photosynthetic rate was correlated with an increase in both the activation state of Rubisco and the total k(cat) (fully activated specific activity) of the enzyme. Evidence presented here suggests that a change in the pool size of the naturally occurring tight binding inhibitor of Rubisco activity, 2-carboxyarabinitol 1-phosphate, was responsible for the PFD-dependent change in the total k(cat) of the enzyme. RuBP pool size transiently increased after the increase in PFD, indicating that photosynthesis was limited by the capacity for carboxylation. After 5 to 10 minutes, RuBP pool size was again similar to the pool size at low PFD, presumably because of the increased activity of Rubisco. Following a step decrease in PFD from 500 to 10 micromoles quanta per square meter per second, Rubisco activity declined but at a much slower rate than it had increased in response to a step increase in PFD. This slower rate of activity decline than increase was apparently due to the slower rate of 2-carboxyarabinitol 1-phosphate synthesis than degradation and, to a lesser degree, to slower deactivation than activation. RuBP pool size initially declined following the decrease in PFD, indicating that RuBP regeneration was limiting photosynthesis. As Rubisco activity decreased, RuBP slowly increased to its original level at high PFD. The slow rate of activity loss by Rubisco in this species suggests a biochemical basis for the increased efficiency for CO(2) assimilation of successive lightfleck use by species such as A. macrorrhiza.

Relation of light and nitrogen source to growth, nitrate reductase and glutamine synthetase activity of jack pine seedlings

Two‐month‐old jack pine (Pinus banksiana Lamb.) seedlings were placed in a greenhouse where both nitrogen source and light level were varied. After 4 months, whole seedling biomass, leaf biomass and relative growth rate were greatest in seedlings grown with NH+4/NO/NO−3‐N and full light (FL) and least in seedlings grown with NO −3‐N and low light (LL). NO −3‐seedlings grown under full light and NH+4/NO−3‐seedlings grown under low light were approximately equal. This indicates that the extra carbon costs of assimilating only NO−3‐N were similar to the reduction of carbon fixation resulting from a 50% decrease in photon flux density. Percentage and total nitrogen content of needles were greater in seedlings grown under low light independent of nitrogen fertilization. Percentage and total nitrogen content of roots were higher under low light and lower when fertilized with NO−3.Nitrate reductase (NR) activity was higher in roots than in needles, while glutamine synthetase (GS) activity was higher in needles than in roots. Low light resulted in decreased NR activity (mg N)−1 in needles, but not in roots. However, no nitrate was detected in the needles in any treatment. GS activity, on the other hand, was greater under low light in both needles and roots. GS activity in needles is most likely involved with the reassimilation rather than the initial assimilation of ammonium. Some implications of these shifts in enzymatic activity for ecological phenomena in forests are discussed.