Carbonic Anhydrase,Photosynthesis, and Seed Yield in Mustard Plants Treated with Phytohormones

The leaves of 30-d-old plants of Brassica juncea Czern & Coss cv. Varuna were sprayed with 10^–6 M aqueous solutions of indole-3-yl-acetic acid (IAA), gibberellic acid (GA₃), kinetin (KIN), and abscisic acid (ABA) or 10^–8 M of 28-homobrassinolide (HBR). All the phytohormones, except ABA, improved the vegetative growth and seed yield at harvest, compared with those sprayed with deionised water (control). HBR was most prominent in its effect, generating 32, 30, 36, 70, 25, and 29 % higher values for dry mass, chlorophyll content, carbonic anhydrase (E.C. 4.2.1.1) activity, and net photosynthetic rate in 60-d-old plants, pods per plant, and seed yield at harvest, over the control, respectively. The order of response to various hormones was HBR > GA₃ > IAA > KIN > control > ABA.     

An in situ study of photosynthetic oxygen exchange and electron transport rate in the marine macroalga Ulva lactuca (Chlorophyta)

Direct comparisons between photosynthetic O₂ evolution rate and electron transport rate (ETR) were made in situ over 24 h using the benthic macroalga Ulva lactuca (Chlorophyta), growing and measured at a depth of 1.8 m, where the midday irradiance rose to 400–600 μmol photons m⁻² s⁻¹. O₂ exchange was measured with a 5-chamber data-logging apparatus and ETR with a submersible pulse amplitude modulated (PAM) fluorometer (Diving-PAM). Steady-state quantum yield ((F_m′−F_t)/F_m′) decreased from 0.7 during the morning to 0.45 at midday, followed by some recovery in the late afternoon. At low to medium irradiances (0–300 μmol photons m⁻² s⁻¹), there was a significant correlation between O₂ evolution and ETR, but at higher irradiances, ETR continued to increase steadily, while O₂ evolution tended towards an asymptote. However at high irradiance levels (600–1200 μmol photons m⁻² s⁻¹) ETR was significantly lowered. Two methods of measuring ETR, based on either diel ambient light levels and fluorescence yields or rapid light curves, gave similar results at low to moderate irradiance levels. Nutrient enrichment (increases in [NO₃ ⁻], [NH₄ ⁺] and [HPO₄ ^2-] of 5- to 15-fold over ambient concentrations) resulted in an increase, within hours, in photosynthetic rates measured by both ETR and O₂ evolution techniques. At low irradiances, approximately 6.5 to 8.2 electrons passed through PS II during the evolution of one molecule of O₂, i.e., up to twice the theoretical minimum number of four. However, in nutrient-enriched treatments this ratio dropped to 5.1. The results indicate that PAM fluorescence can be used as a good indication of the photosynthetic rate only at low to medium irradiances. This revised version was published online in June 2006 with corrections to the Cover Date.     

The content of endogenous hormones and sugars in the process of early somatic embryogenesis in the tree fern <Emphasis Type="Italic">Cyathea delgadii</Emphasis> Sternb.

Somatic embryogenesis (SE) of Cyathea delgadii presents a model system for investigating the mechanisms associated with the acquisition of embryogenic competence by single epidermal cells of stipe explants cultured on plant growth regulator-free medium. The present work reveals relationship between endogenous hormone and sugar content in the process of early SE in C. delgadii. By comparing two types of initial explants, i.e. incapable (non-etiolated) and capable (etiolated) of SE, it was established that in etiolated explants, the glucose, fructose, sucrose, and abscisic acid (ABA) contents diminished, but indole-3-acetic acid (IAA) and cytokinins (CKs; i.e. cis/trans zeatin, cis/trans-zeatin riboside, kinetin, kinetin riboside, isopentenyladenosine) contents increased. The ratios between phytohormones revealed that a high concentration of ABA is the main factor inhibiting SE induction. Because of explant excision, a dramatic reduction in concentration of all phytohormones studied was observed, but hormonal balance and sugar content remained almost unchanged. During the 14-day-long culture, the ABA/CKs and ABA/IAA ratios remained constant, whereas the greatest differences were detected for the IAA/CKs and Z-type/iPA cytokinin ratios. Excluding day 6 of culture, cytokinins were found to be the predominant phytohormones over IAA. An almost 12-fold increase in soluble sucrose concentration at day 6 of culture might be the switch to the SE expression phase. Frequent cell divisions leading to somatic embryo formation are clearly associated with increase in trans-zeatin riboside content.     

Photoacclimation characteristics of Sargassum thunbergii germlings under different light intensities

The photosynthesis and growth responses of Sargassum thunbergii germlings to different light intensities (10, 60, and 300 μmol photons m^?2 s^?1) were investigated. Maximum photochemical efficiency (F _v/F _m), rapid light curves (RLCs), and photochemical and non-photochemical quenching (qP and NPQ) were estimated by a pulse amplitude-modulated fluorometer. The photosynthesis of S. thunbergii germlings exhibited different properties to optimize light capture and utilization. The excitation pressure (1???qP) was rapidly increased to approximately 0.27 showing that germlings responded to high light by chronic photoinhibition with an accumulation of closed reaction centers, which ultimately resulted in a slow growth. This was accompanied by a reduced F _v/F _m with time and a development of high capacity for NPQ. Although F _v/F _m in moderate-light germlings did not fully recover overnight, germlings demonstrated a less severe chronic photoinhibition considering the reduced degree of excitation pressure accumulation of approximately 0.15. The relative stability of photosynthetic capacity (rETR_max, E _k, and α) could endow germlings with the highest relative growth rate (RGR) of approximately 9.3 % day^?1 in moderate light. By contrast, low-light germlings demonstrated high F _v/F _m and F _o, corresponding high α collectively suggested greater efficiency of light absorption and energy transformation. Sustained increases in electron transport capacity (rETR_max and E _k) occurred in low-light germlings, which resulted in a stable RGR of over 8.2 % day^?1. Consequently, S. thunbergii germlings are considered to prefer low light regimes and have a relative capacity of moderate and high light tolerance. However, the light acclimation to oversaturating conditions is at the cost of slow growth to maintain survival.     

An inter-basin comparison of nutrient limitation and the irradiance response of pulse-amplitude modulated (PAM) fluorescence in Lake Erie phytoplankton

This research examined the application of the maximum quantum efficiency (F _v/F _m) and relative electron transport rate versus irradiance curves (rETR) as a rapid, sensitive assessment of Lake Erie phytoplankton nutrient status. I evaluated the potential benefits of the variable fluorescence parameters by comparing these parameters with chemical and physiological nutrient status assays. I tested the hypothesis that F _v/F _m and rETR curves could diagnose nutrient status in natural lake phytoplankton and be capable of discriminating which inorganic nutrient is limited temporally and spatially. F _v/F _m was on average highest in the more eutrophic west basin (WB) and lowest in the more oligotrophic central basin (CB). According to the chemical and physiological indicators, P deficiency was most severe in the CB during summer stratification and N deficiency was strongest in the WB during isothermal conditions. Like F _v/F _m, rETR at light saturation (rETR_max) and the initial slope of the rETR versus irradiance curve (α) decreased as the severity of N and P deficiency increased. Amendment with N or P stimulated increased F _v/F _m, rETR_max, and α in N- and P-limited samples, respectively, and abolished the photoinhibition apparent in rETR curves of nutrient-limited samples. These results supported the view that the N and P deficiency assays, and corresponding variations of variable fluorescence parameters, were valid indicators of widely variable N and P deficiency in the phytoplankton, and could be used to provide a promising tool in determining phytoplankton nutrient status. Contrary to my hopes, it did not appear that rETR–irradiance curves could discriminate between N and P deficiency. Identification of the most limiting nutrient still demanded additional information beyond the variable fluorescence measurements.     

Endogenous phytohormone profile during oat (Avena sativa L.) haploid embryo development

The development of embryos requires interaction of many endogenous hormones. The aim of the study was to determine which endogenous phytohormones are involved in the process of oat (Avena sativa L.) haploidization. Oat haploids were obtained by wide crossing with Zea mays L. The hormonal profiles of the ovaries with (OE) and without developed embryo (OWE) were compared. Phytohormone contents were measured by UHPLC coupled with mass spectrometer. The total content of indole-3-acetic acid (IAA), trans-zeatin (tZ), and kinetin (KN) in OE was significantly higher than in OWE. 4-Chloroindole-3-acetic acid was detected only in OWE. There were no differences between OE and OWE in the content of gibberellins (GA₁, GA₃, GA₄, GA₆, GA₇) and stress hormones (abscisic, salicylic, jasmonic acids). Content of endogenous KN was highly negatively correlated with the percentage of haploid embryos, germinated haploid embryos, haploid plants on MS (in vitro), haploid plants in soil (ex vitro), and doubled haploid lines. The tZ content negatively correlated with the frequency of haploid embryo formation, germination, and haploid plants obtained in vitro, as opposed to GA₁, which correlated positively. A positive correlation was found between IAA and tZ in OE, whereas in OWE it was a negative correlation. The profiles of phytohormones in OE and OWE were determined; however, their mode of action needs to be clarified.

     

Susceptibility of green leaves and green flower petals of CAM orchid <Emphasis Type="Italic">Dendrobium</Emphasis> cv. Burana Jade to high irradiance under natural tropical conditions

Photosynthetic rates of green leaves (GL) and green flower petals (GFP) of the CAM plant Dendrobium cv. Burana Jade and their sensitivities to different growth irradiances were studied in shade-grown plants over a period of 4 weeks. Maximal photosynthetic O₂ evolution rates and CAM acidities [dawn/dusk fluctuations in titratable acidity] were higher in leaves exposed to intermediate sunlight [a maximal photosynthetic photon flux density (PPFD) of 500–600 μmol m⁻² s⁻¹] than in leaves grown under full sunlight (a maximal PPFD of 1 000–1 200 μmol m⁻² s⁻¹) and shade (a maximal PPFD of 200–250 μmol m⁻² s⁻¹). However, these two parameters of GFP were highest in plants grown under the shade and lowest in full sun-grown plants. Both GL and GFP of plants exposed to full sunlight had lower predawn F_v/F_m [dark adapted ratio of variable to maximal fluorescence (the maximal photosystem 2 yield without actinic irradiation)] than those of shade-grown plants. When exposed to intermediate sunlight, however, there were no significant changes in predawn F_v/F_m in GL whereas a significant decrease in predawn F_v/F_m was found in GFP of the same plant. GFP exposed to full sunlight exhibited a greater decrease in predawn F_v/F_m compared to those exposed to intermediate sunlight. The patterns of changes in total chlorophyll (Chl) content of GL and GFP were similar to those of F_v/F_m. Although midday F_v/F_m fluctuated with prevailing irradiance, changes of midday F_v/F_m after exposure to different growth irradiances were similar to those of predawn F_v/F_m in both GL and GFP. The decreases in predawn and midday F_v/F_m were much more pronounced in GFP than in GL under full sunlight, indicating greater sensitivity in GFP to high irradiance (HI). In the laboratory, electron transport rate and photochemical and non-photochemical quenching of Chl fluorescence were also determined under different irradiances. All results indicated that GFP are more susceptible to HI than GL. Although the GFP of Dendrobium cv. Burana Jade require a lower amount of radiant energy for photosynthesis and this plant is usually grown in the shade, is not necessarily a shade plant.     

不同剂量~(137)Cs-γ辐射对毛竹幼苗叶片叶绿素荧光参数的影响

利用不同剂量的137Cs-γ射线对毛竹(Phyllostachys heterocycla ‘Pubescens’)种子进行辐射,测定实生苗叶片中的光合色素含量和叶绿素荧光参数等指标,探讨辐射对毛竹幼苗生长的影响,为筛选有利的突变单株奠定良好基础。结果表明:30或60Gy的137Cs-γ射线辐射后,毛竹幼苗的光合色素含量以及最大荧光强度(Fm)、可变荧光强度(Fv)、PSII最大光化学效率(Fv/Fm)、PSII的潜在活性(Fv/Fo)、PSII实际光化学效率(Yield)和表观光合电子传递速率(ETR)等荧光参数值均高于90Gy辐射处理,说明较低剂量辐射后PSII反应中心的能量捕获效率高,且具有较强的光合能力;而90Gy的137Cs-γ射线辐射对毛竹的影响则与之相反。不同处理剂量之间叶片光能耗散程度以及表观光合电子传递速率-光合有效辐射(ETR-PAR)响应曲线的分析结果也进一步证实了以上结论。     

Growth and pigment content of wheat as influenced by the combined effects of salinity and growth regulators

A field experiment was conducted to investigate the effects of presoaking the wheat grains (Triticum aestivum L.) in different levels of salinity (33 or 66 mM) and in growth regulators (indolyl-3-acetic acid, IAA at SO g m^-3, gibberellic acid, GA₃ at 100 g m^-3, or kinetin at 100 g m_-3) on the shoot growth and pigment content of the developing wheat flag leaf. Salinity at 33 or 66 mM led to an insignificant increase in the fresh and dry masses as well as in the shoot diameter and shoot length, but it attenuated the flag leaf area. In the majority of cases, salinity increased the chlorophyll (Chla, Chlb) and carotenoid contents as well as the number of chloroplasts per a mesophyll cell. The growth in the wheat shoot of the saline-treated plants was, in general, stimulated in response to presoaking the grains in kinetin or GA₃. On the other hand, IAA + salinity led to a negligible effect on the growth in the wheat plants particularly at the early stages of growth. The presoaking of grains in NaCl at 33 mM + IAA or 66 mM + kinetin induced a marked increase in the pigment content of the wheat flag leaf particularly at the early stages of growth. The interaction between salinity and phytohormones increased the number of chloroplasts; kinetin was the most effective.     

Somatic embryogenesis in Encephalartos cycadifolius

Callus cultures of Encephalartos cycadifolius were established from zygotic embryo explants on a modified B5 medium containing 1 mg l^–1 2,4-D and 1 mg l^–1 kinetin. Callus was transferred to media containing various combinations of 2,4-D and kinetin for improvement of somatic embryogenesis. Somatic embryos were produced on media with several growth regulator combinations. The somatic embryos developed from proembryos, which developed long suspensors. A dicotyledonary embryo formed at the distal end of the suspensor. The embryos turned green in light. When transferred to a medium containing 1 mg l^–1 ABA the somatic embryos matured. The suspensors desiccated and these embryos rooted when transferred to a medium without phytohormones.Abbreviations ABA abscisic acid - 2,4-D 2,4-dichlorophenoxyacetic acid     

Fluorescence parameters of White Sea phytoplankton under different nitrogen sources

We investigated dependence of fluorescence parameters and phytoplankton biomass on the nitrogen source and irradiance in enriched flask studies with White Sea plankton from August-September 2007. Phytoplankton was exposed in situ for 18 d with addition of 180 μM/L of nitrogen in the forms of nitrate, urea, ammonia, and glycine under two levels of irradiance. Maximum quantum efficiency of PS2 (F_v/F_m) was determined in the samples adapted to darkness. Rapid light curves were obtained for each sample with the sequential increase of light intensity (8 levels). The maximal relative electron transport rate (rETR_max), the maximum light utilization coefficient (α), and the nonphotochemical quenching (NPQ) were calculated. The phytoplankton abundance increased on nitrogen addition, and the photosynthetic parameters changed. The values F_v/F_m reached 0.64–0.71, which indicated a good physiological state of algae and lack of nitrogen limitation. The dynamics of rETR_max and NPQ depended of the nitrogen source and irradiance, while α did not depend on nitrogen addition.     

The photosynthetic performance of the tropical seagrass Halophila ovalis in the upper intertidal

Some ecophysiological adaptation strategies of the tropical seagrass Halophila ovalis were investigated with respect to this plant's ability to grow in the upper intertidal in either monospecific pools (but not together with other intertidal species) or emergent and exposed to high temperatures and irradiances during several hours every day. It was found that Halophila ovalis could raise the pH in simulated pools to 8.6, while the two other major (biomass wise) intertidal seagrasses raised the pH to 8.8 (Cymodocea rotundata) and 9.2 (Thalassia hemprichii). In situ, midday pH values of 8.5, 8.7 and 9.0 were recorded in pools inhabiting the three species, respectively. It was further found that photosynthetic electron transport rates (ETR) measured continuously in situ for one leaf during a diurnal cycle followed the irradiance up to a daily maximal value of 2200 μmol photons m⁻² s⁻¹, but dropped by ca. 50% when the leaf became air exposed just before noon. This drop in ETR upon emergence was verified by “point measurements”, while ETRs of leaves that grew in small pools formed as the tide receded followed the irradiance more closely. Similarly, F_v/F_m measured after 15 min of dark adaptation decreased by ca. 50% in emergent leaves during midday, but maintained higher daily values in the submerged leaves.     

The influence of ABA on water relation, photosynthesis parameters, and chlorophyll fluorescence under drought conditions in two maize hybrids with contrasting drought resistance

Drought is a major limitation of maize cultivation in Brazil. Agronomic and physiological practices have been considered to overcome this stress and consequently, increase grain production. The present study investigated the role of abscisic acid (ABA) application in some physiological parameters, in two hybrids with contrasting drought resistance (DKB 390 and BRS 1030 resistant and sensitive, respectively). Contrasting resistance to drought in these genotypes was determined in previous studies. Water deficit was imposed for 10 days at flowering stage, in association with the application of 100 μM abscisic acid on plant canopy. Evaluations of gas exchange, chlorophyll fluorescence, relative water content (RWC), and endogenous ABA content were performed during stress period and also at water recovery (recovery irrigation). A significant functional relationship was observed between RWC and the parameters of gas exchange and fluorescence. During water recovery, no differences were observed among the treatments. DKB 390 presented higher photosynthesis rate (P _n) and electron transport rate (ETR) under water stress, while BRS 1030 presented higher intercellular CO₂ concentration (C _i) and lower photochemical quenching (qP), non-photochemical quenching (NPQ), and lower F _v/F _m ratio. DBK 390 was more responsive to ABA application than BRS 1030, presenting higher endogenous ABA content in the first day of stress. DBK 390 with ABA application reduced the effect of water stress through maintenance of water status, an increase of photosynthetic parameters, and a decrease of decline in the functions of photosystem II during stress.     

THE SHORT‐TERM EFFECT OF IRRADIANCE ON THE PHOTOSYNTHETIC PROPERTIES OF ANTARCTIC FAST‐ICE MICROALGAL COMMUNITIES1

Although sea‐ice represents a harsh physicochemical environment with steep gradients in temperature, light, and salinity, diverse microbial communities are present within the ice matrix. We describe here the photosynthetic responses of sea‐ice microalgae to varying irradiances. Rapid light curves (RLCs) were generated using pulse amplitude fluorometry and used to derive photosynthetic yield (Φ_PSII), photosynthetic efficiency (α), and the irradiance (E_k) at which relative electron transport rate (rETR) saturates. Surface brine algae from near the surface and bottom‐ice algae were exposed to a range of irradiances from 7 to 262 μmol photons · m^?2 · s^?1. In surface brine algae, Φ_PSII and α remained constant at all irradiances, and rETR_max peaked at 151 μmol photons · m^?2 · s^?1, indicating these algae are well acclimated to the irradiances to which they are normally exposed. In contrast, Φ_PSII, α, and rETR_max in bottom‐ice algae reduced when exposed to irradiances >26 μmol photons · m^?2 · s^?1, indicating a high degree of shade acclimation. In addition, the previous light history had no significant effect on the photosynthetic capacity of bottom‐ice algae whether cells were gradually exposed to target irradiances over a 12 h period or were exposed immediately (light shocked). These findings indicate that bottom‐ice algae are photoinhibited in a dose‐dependent manner, while surface brine algae tolerate higher irradiances. Our study shows that sea‐ice algae are able to adjust to changes in irradiance rapidly, and this ability to acclimate may facilitate survival and subsequent long‐term acclimation to the postmelt light regime of the Southern Ocean.     

Salicylic acid may be involved in the regulation of drought-induced leaf senescence in perennials: A case study in field-grown Salvia officinalis L. plants

Leaf senescence is a highly regulated physiological process that contributes to nutrient remobilization during stress, thus allowing the rest of the plant to benefit from the nutrients accumulated during the life span of the leaf. Here we studied drought-induced leaf senescence in a perennial plant, common sage (Salvia officinalis L.) grown under Mediterranean field conditions, with an emphasis on the possible involvement of the phytohormones, salicylic acid and jasmonic acid in the process. The initial stages of leaf senescence (0–27 days of water deficit) were characterized by salicylic acid accumulation (by 80%) and decrease of jasmonic acid levels (by 40%), which occurred in parallel with a severe loss of photosynthetic pigments (up to 65%) and increases in the de-epoxidation state (DPS) of the xanthophyll cycle (by 55%), while the maximum efficiency of photosystem II (F_v/F_m ratio) was maintained above 0.80, thus indicating the absence of damage to the photosynthetic apparatus. The latest stages of leaf senescence (until 42 days of water deficit) were instead characterized by maintenance of the levels of jasmonic acid and salicylic acid, while β-carotene and the F_v/F_m ratio decreased significantly, which was followed by cell death. Exogenous applications of methyl salicylic acid in leaves of water-stressed plants led to reductions in chlorophyll levels, thus confirming the promoting effects of salicylic acid on leaf senescence. It is therefore concluded that salicylic acid may be involved, together with other phytohormones, in the regulation of drought-induced leaf senescence in perennials.     

Changes in Chlorophyll Fluorescence in Maize Plants with Imposed Rapid Dehydration at Different Leaf Ages

A comparison of the effects of a rapidly imposed water deficit with different leaf ages on chlorophyll a fluorescence and gas exchange was performed in maize (Zea mays L.) plants. The relationships between photosynthesis and leaf relative turgidity (RT) and ion leakage were further investigated. Leaf dehydration substantially decreased net photosynthetic rate (A) and stomatal conductance (G _s), particularly for older leaves. With dehydration time, F _v /F _m maintained a relatively stable level for youngest leaves but significantly decreased for the older leaves. The electron transport rate (ETR) sharply decreased with intensifying dehydration and remained at lower levels during continuous dehydration. The photochemical quenching of variable chlorophyll fluorescence (q _P) gradually decreased with dehydration intensity for the older leaves but increased for the youngest leaves, whereas dehydration did not affect the nonphotochemical chlorophyll fluorescence quenching (NPQ) for the youngest leaves but remarkably decreased it for the older leaves. The leaf RT was significantly and positively correlated with its F _v /F _m, ETR, and q _P, and the leaf ion leakage was significantly and negatively correlated with F _v /F _m and NPQ. Our results suggest that the photosynthetic systems of young and old leaves decline at different rates when exposed to rapid dehydration.     

Small scale vertical gradients of Arctic ice algal photophysiological properties

Photosynthetic parameters of phytoplankton and sea ice algae from landfast sea ice of the Chukchi Sea off Point Barrow, Alaska, were assessed in spring 2005 and winter through spring 2006 using Pulse Amplitude Modulated (PAM) fluorometry including estimates of maximum quantum efficiency (F _v/F _m), maximum relative electron transport rate (rETR_max), photosynthetic efficiency (α), and the photoadaptive index (E _k). The use of centrifuged brine samples allowed to document vertical gradients in ice algal acclimation with 5 cm vertical resolution for the first time. Bottom ice algae (0–5 cm from ice–water interface) expressed low F _v/F _m (0.331–0.426) and low α (0.098–0.130 (μmol photons m⁻²s⁻¹)⁻¹) in December. F _v/F _m and α increased in March and May (0.468–0.588 and 0.141–0.438 (μmol photons m⁻²s⁻¹)⁻¹, respectively) indicating increased photosynthetic activity. In addition, increases in rETR_max (3.3–16.4 a.u.) and E _k (20–88 μmol photons m⁻² s⁻¹) from December to May illustrates a higher potential for primary productivity as communities become better acclimated to under-ice light conditions. In conclusion, photosynthetic performance by ice algae (as assessed by PAM fluorometry) was tightly linked to sea ice salinity, temperature, and inorganic nutrient concentrations (mainly nitrogen).     

Protective Action of Abscisic Acid Against the Inhibition of Photosynthesis of Barley Leaves by Bisulphite

The inhibition of photosynthetic activity by bisulphite was studied in intact leaves of abscisic acid (ABA)-treated and non-treated (control) barley plants. ABA inhibited the photosynthetic process as evidenced by lower values of chlorophyll fluorescence kinetic parameters F_v/F_m (photosystem 2 activity) and R_fd (vitality index, related to the whole photosynthetic activity) compared with ABA-non-treated plants. After bisulphite treatment, the extent of inhibition was smaller in ABA-treated plants than in the control ones indicating a protective effect of ABA. The protective action sites of ABA were the Q_A reduction and the Calvin cycle. This revised version was published online in September 2006 with corrections to the Cover Date.     

A COMPARISON OF PHOTOSYNTHETIC ELECTRON TRANSPORT RATES IN MACROALGAE MEASURED BY PULSE AMPLITUDE MODULATED CHLOROPHYLL FLUOROMETRY AND MASS SPECTROMETRY

The relationship between whole chain photosynthetic electron transport and PSII activity was investigated in Porphyra columbina (Montagne) (Rhodophyta), Ulva australis (Areschoug) (Chlorophyta), and Zonaria crenata ( J. Agardh) (Phaeophyta). Mass spectrometric measurements of gross O₂ evolution and gross O₂ uptake were combined with simultaneous measurement of pulse-modulated chl fluorescence under a range of irradiances and inorganic carbon (C_i) concentrations. At light-limiting irradiance, a good correlation between gross O₂ evolution and the electron transport rate (ETR) calculated from chl fluorescence ((F_m′− F_s)/F_m′) was found in the optically thin species (Ulva and Porphyra). The calculated ETR was equivalent to the theoretical electron requirement in these species but overestimated gross O₂ evolution in the thicker species Zonaria. In saturating light, especially when C_i availability was low, ETR overestimated gross O₂ evolution in all species. Excess electron flow could not be accounted for by an increase in gross O₂ uptake; thus neither Mehler-ascorbate-peroxidase reaction nor the photosynthetic carbon oxidation cycle were enhanced at high irradiance or low C _i. Alternative explanations for the loss of correlation include cyclic electron flow around PSII that may be engaged under these conditions or nonphotochemical energy quenching within PSII centers. The loss of correlation between ETR and linear photosynthetic electron flow as irradiance increased from limiting to saturating or at low C_i availability and in the case of optically thick thalli limits the application of this technique for measuring photosynthesis in macroalgae.     

Phytohormone effects on hydrolytic activity of phosphohydrolases in red beet (Beta vulgaris L.) tonoplasts

The effects of indole-3-acetic acid (IAA), abscisic acid (ABA), gibberellic acid (GA₃) and kinetin on the hydrolytic activity of proton pumps (adenosine triphosphatase, H⁺-ATPase, pyrophosphatase, H⁺-PPase) of tonoplasts isolated from stored red beet (Beta vulgaris L. cv. Bordo) roots were studied. Results suggest that the phytohormones can regulate the hydrolytic activities of H⁺-ATPase and H⁺-PPase of the vacuolar membrane. Each of the proton pumps of the tonoplast has its own regulators in spite of similar localization and functions. IAA and kinetin seem to be regulators of the hydrolytic activity for H⁺-PPase whereas for H⁺-ATPase it may be GA₃. Stimulation of enzyme activity by all hormones occurred at concentrations of 10^–6 to 10^–7 M.Abbreviations IAA indole-3-acetic acid - ABA abscisic acid - GA₃ gibberellic acid - H⁺-ATPase adenosine triphosphatase - H⁺-PPase pyrophosphatase - ATP adenosine triphosphate - Tris Tris (hydroxymethyl)-aminomethane - MES (2[N-Morpholino]) ethane sulfonic acid - EDTA ethylene diamine tetraacetic acid - P_i inorganic phosphate