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Drought was induced in chickpea ( Cicer arietinum L.) genotypes (ChK 3226 and ILC 3279) differing in yield capacity. Water stress (S1, RWC around 55–50%; S2, RWC ≤ 40%) drastically reduced stomatal conductance ( g s ) and net photosynthetic rate ( P N ) in both genotypes. ILC 3279 showed greater photosynthetic capacity ( A max ) decreases. Maximum PSII photochemical efficiency (F v /F m ), photochemical quenching (q P ), total chlorophylls (Chls) and carotenoids (Cars) content showed stability in both genotypes under stress, but in S2 ILC 3279 presented an increase in basal fluorescence (F 0 ) and a greater reduction in estimation of quantum yield of linear electron transport (Φ e ) than ChK 3226. Membrane damage evaluated by electrolyte leakage occurred earlier and was greater in ILC 3279. It also presented a decrease of total fatty acids (TFA) along drought, while in ChK 3226 greater amounts of TFA were observed in S1. In rehydration, P N of S1 plants completely recovered (ILC 3279) or remained slightly below control (ChK 3226). As regards S2 plants, ILC 3279 showed stronger P N and g s reductions than ChK 3226, despite both genotypes totally recovered A max and chlorophyll (Chl) a fluorescence. ChK 3226 recovered more efficiently from membrane damage. Under control conditions, greater amounts of most of the studied soluble metabolites occurred in ChK 3226 plants. Malate and citrate decreased with water stress (S2) in both genotypes. Sucrose and pinitol (that had a higher concentration than sucrose in both genotypes) increased in ILC 3279 (S1 and S2), and decreased in ChK 3226 (S2). In ILC 3279 proline and asparagine followed similar patterns. Genotypes showed a similar shoot dry mass (DM) in control plants, but root DM was higher in ChK 3226. Drought reduced root and shoot DM in ChK 3226 already under S1, while in ILC 3279 root DM was unaffected by drought and shoot biomass decreased only in S2. Root/shoot ratio was always higher in ChK 3226 but tended to decrease under stress, while the opposite was observed in ILC 3279. No pods were obtained from control plants of both genotypes, or droughted ILC 3279 plants. ChK 3226 produced pods under S1 (higher yield) and S2. Under stress conditions, ChK 3226 was less affected in photosynthetic activity and membrane integrity, showing a better tolerance to drought. This agrees with the better yield of this genotype under water stress. Distinct strategies seem to underlie the different physiological responses of the two genotypes to water deficit. In spite of its significant solutes accumulation, ILC 3279 was more affected in photosynthetic activity and membrane integrity during water stress than ChK 3226, which showed better yield under drought. A relation could not be established between solutes accumulation of ILC 3279 and yield.

Effect of drought on the mechanisms of energy dissipation was evaluated in two-month-old Arachis hypogaea cvs. 57–422, 73–30, and GC 8–35. Plants were submitted to three treatments: control (C), mild water stress (S1), and severe water stress (S2). Photosynthetic performance was evaluated as the Hill and Mehler reactions. These activities were correlated with the contents of the low and high potential forms of cytochrome (cyt) b 559, plastoquinone, cyt b 563, and cyt f. Additionally, the patterns of carotenoids and chlorophylls (Chls), as well as the alterations of Chl a fluorescence parameters were studied. Under mild water stress the regulatory mechanism at the antennae level was effective for 57–422 and GC 8–35, while in the cv. 73–30 an overcharge of photosynthetic apparatus occurred. Relative to this cv., under S1 the stability of carotene and the dissipative cycle around photosystem (PS) 2 became an important factor for the effective protection of the PS2 reaction centres. The cyclic electron flow around PS1 was important for energy dissipation under S1 only for the cvs. 57–422 and 73–30.

The photosynthetic response of three Arachis hypogaea L. cultivars (57-422, 73-30, and GC 8-35) grown for two months was measured under water available conditions, severe water stress, and 24, 72, and 93 h following re-watering. At the end of the drying cycle, all the cultivars reached dehydration, relative water content (RWC) ranging between 40 and 50 %. During dehydration, leaf stomatal conductance (gs), transpiration rate (E), and net photosynthetic rate (PN) decreased more in cvs. 57-422 and GC 8-35 than in 73-30. Instantaneous water use efficiency (WUEi) and photosynthetic capacity (Pmax) decreased mostly in cv. GC 8-35. Except in cv. GC 8-35, the activity of photosystem 1 (PS1) was only slightly affected. PS2 and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) were the main targets of water stress. After re-watering, cvs. 73-30 and GC 8-35 rapidly regained gs, E, and PN activities. Twenty-four hours after re-watering, the electron transport rates and RuBPCO activity strongly increased. PN and Pmax fully recovered later. Considering the different photosynthetic responses of the studied genotype, a general characterisation of the interaction between water stress and this metabolism is presented.

Gas exchanges and leaf water potential (Ψw) of six-years-old trees of fourteen Prunus amygdalus cultivars, grafted on GF-677, were studied in May, when fruits were in active growing period, and in October, after harvesting. The trees were grown in the field under rain fed conditions. Predawn Ψw showed lower water availability in October compared with May. The lowest Ψw values at midday in May increased gradually afterwards, while in October they decreased progressively until night, suggesting a higher difficulty to compensate the water lost by transpiration. However, relative water content (RWC) measured in the morning was similar in both periods, most likely due to some rainfall that occurred in September and first days of October that could be enough to re-hydrate canopy without significantly increasing soil water availability. The highest net photosynthetic rate (PN) was found in both periods early in the morning (08:00–11:00). Reductions in PN from May to October occurred in most cultivars except in José Dias and Ferrastar. In all cultivars a decrease in stomatal conductance (gs) was observed. Photosynthetic capacity (Pmax) did not significantly change from spring to autumn in nine cultivars, revealing a high resistance of photosynthetic machinery of this species to environmental stresses, namely high temperature and drought. Osmotic adjustment was observed in some cultivars, which showed reductions of ca. 23 % (Duro d' Estrada, José Dias) and 15 % (Tuono) in leaf osmotic potential (Ψπ). Such decreases were accompanied by soluble sugars accumulation. The Portuguese cultivar José Dias had a higher photosynthetic performance than the remaining genotypes.

Twenty-day-old barley (Hordeum vulgare L. cv. Ribeka) plants grown as sand culture were exposed to Cu treatment (0, 10, 15 and 20 mg Cu kg-1 sand) for ten days. The effects of excess Cu on both growth and photosynthetic performance were studied in order to identify the most sensitive probes implicating a further development of screening test for Cu tolerance within barley genotypes. The results obtained indicated that stomata conductance and photosynthetic electron transport linked to PSII+OEC exhibited the highest sensitivity to excess Cu, followed by plant dry weigh accumulation, leaf area formation, net photosynthetic rate, photosynthetic electron transport linked to PSI and PSII-OEC. It was concluded that leaf gas exchange parameters, plant dry weight accumulation and leaf area formation present an effective plant test system for screening for barley genotypes with higher Cu tolerance.

Ahipa (Pachyrhizus ahipa) is a legume crop, which produces carbohydrate-rich tuberous roots and seeds rich in protein and oil. In the present work, we studied the effect of different agronomic practices and climatic conditions on root and seed yield in order to make a preliminary assessment of the yield potential under different managements for the ahipa crop in south-western Europe. Sowing date affected productivity when delayed, because of growth season shortening. Reproductive pruning greatly increased root yield. Increasing planting density affected root and fruit growth per plant but increased yield to a certain extent. Seed inoculation with effective rhizobia greatly increased root and seed production. Low temperature is a main factor to be considered as it reduced productivity in areas of cool nights. Ahipa has a low environmental impact and low input requirement (fertilizer, pesticides), providing an attractive alternative to traditional sources of carbohydrates for conserving non-renewable resources and maintaining farmer profitability. Competitive yields for the simultaneous production of starch, feed protein and industrial oil may be obtained with low investment using available landraces.

Pachyrhizus ahipa (Wedd.) Parodi, originally from Latin America, is an agronomy interesting legume crop due to high seed protein content and saccharides-rich tuber root. Its capacity of adaptation to Mediterranean climate, where heat and water stress are frequently associated, is being tested. Two accessions of P. ahipa (AC 102 and AC 524) differing in field production were compared as concerns the effects of water stress and high temperature on photosynthetic performance. Membrane integrity was also evaluated through electrolyte leakage (injury index, I%), lipid composition, and ultrastructure observations. Short-term heat stress (40 °C) did not affect net photosynthetic rate (PN), stomatal conductance (gs), and most of fluorescence parameters in both accessions, what was consistent with low electrolyte leakage. However, photosynthetic capacity (Pmax) showed a significant reduction, AC 524 being more affected than AC 102. Relative water content (RWC) below 70 % caused a drastic decrease in PN and gs. Fluorescence parameters, Pmax, and I% were affected in the two accessions, which also presented a strong reduction (42 %) in total fatty acids (TFA). Contents of galactolipids were drastically reduced, and changes in their saturation also occurred, namely a decrease in linolenic acid (C18:3) percentage of monogalactosyl-diacylglycerol (MGDG) in both accessions. Thylakoid ultrastructure in AC 524 submitted to drought showed disorganisation of grana stacking. Mitochondria presented signs of injured cristae. When water-stressed plants were subjected to high temperature, photosynthesis and fluorescence parameters did not show significant additional changes in both accessions. The exposure of drought stressed plants to 40 °C further increased electrolyte leakage in AC 524, but not in AC 102. Chloroplasts, mitochondria, and plasmalemma showed an increased disorganisation. Vesicles appeared in the cytoplasm, which became electron-transparent, reflecting a strong reduction in the number of ribosomes. Hence AC 102 was less affected than AC 524 as regards some components of photosynthetic process, namely Pmax and membrane integrity. This could account for its better yield production previously observed in field grown plants.

A suitable light quantity and quality is essential for optimal photosynthetic metabolism. Using combinations of three lamp types, the impact of the quality of artificial light conditions on the photosynthetic apparatus of leaves developed in growth chambers was analysed. The VIALOX-Planta lamps are quite poor outside the green to orange (520620 nm) wavelength range, while the HQI-BT lamps present a more uniform spectral intensity between 425 and 650 nm (blue to red). The halogen lamps are particularly rich in the red and far red range of the electromagnetic spectra. The lamps also differ in the red:far red ratio, which were 3.07 (VIALOX), 2.06 (HQI-BT) and 1.12 (halogen). Clear positive effects were detected in most of the photosynthetic parameters in relation to light quality, both at stomatal and mesophyll levels. Despite some species-dependent sensitivity to blue and red/far red wavelengths, observed among the studied parameters, the best photosynthetic performances of the test plants (Packyrhizus ahipa and Piata, a hybrid of Coffea dewevrei x Coffea arabica) were obtained almost always with the reinforcement of blue (HQI-BT lamps), red and far red (halogen lamps) wavelengths and with a red Jar red ratio closer to that observed in nature. This suggests the involvement of more than one photoreceptor family in photosynthetic performance. Under such light conditions, increases in net photosynthesis and stomatal conductance were observed and, despite the moderate effects on photosynthetic capacity, strong effects were observed in the capture and transfer of light energy in the antennae pigments, photochemical efficiency of photosystem II and electron transport. This was related to the striking quantitative and qualitative impacts observed on total chlorophylls and carotenoids, which reached, in some cases, increases of 100 and 200%, respectively. Among carotenoids, increases as high as 9-fold for alpha-carotene were observed (P. ahipa), with chlorophyll (a/b), total (chlorophyll/carotenoid) and carotene (alpha/beta) ratios also strongly affected. This would have affected the structure and stability of photosynthetic membranes which, in turn, affected photosynthetic-related processes (e.g., antennae pigments, photosystem II and electron transport efficiencies). This was particularly clear in the HQI + halogen treatment. The results unequivocally show that light quality could remain a clear limiting factor for leaf/plant development under artificial light conditions, which could be overcome using more than one lamp type, with complementary emission spectra.

Biotech Software & Internet ReportVol. 3, No. 4 Encyclopedia of Life SciencesManuel MatosManuel MatosPublished Online:5 Jul 2004https://doi.org/10.1089/15279160260170319AboutSectionsPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail FiguresReferencesRelatedDetails Volume 3Issue 4Sep 2002 To cite this article:Manuel Matos.Encyclopedia of Life Sciences.Biotech Software & Internet Report.Sep 2002.94-96.http://doi.org/10.1089/15279160260170319Published in Volume: 3 Issue 4: July 5, 2004PDF download

The effects of drought on thylakoid acyl lipid composition, photosynthetic capacity (P max), and electrolyte lekage were evaluated in two-months-old peanut cultivars (57-422, 73-30, GC 8-35) growing in a glasshouse. For lipid studies, plants were submitted to three treatments by withholding irrigation: control (C), mild water stress (S1), and severe water stress (S2). Concerning membrane and photosynthetic capacity stability, drought was imposed by polyethylene glycol (PEG 600). In the cv. 73-30 a sharp decrease in the content of thylakoid acyl lipids was observed, already under S1 conditions, whereas cv. 57-422 was strongly affected only under S2. Cv. GC 8-35 had the lowest content of acyl lipids under control conditions, a significant increase under S1 conditions, and only under S2 a decrease occurred. Thus concerning lipid stability, cv. 73-30 was the most sensitive. Among lipid classes, phospholipids and galactolipids were similarly affected, as was MGDG relatively to DGDG. Water deficit imposed by PEG induced a higher increase in electrolyte leakage in cv. 73-30 than in the other cvs. A positive relationship between acyl lipid concentration and membrane integrity was found in all studied cvs. A positive association between acyl lipid concentration, membrane integrity, and P max was found in the cvs. 57-422 and 73-30.

The effect of drought on plant water relations and photosynthesis of Vigna glabrescens (Vg) and Vigna unguiculata (cvs. 1183, EPACE-1 and Lagoa), which differ in their drought resistance, was compared. With the increase of drought severity, Vg showed a more gradual stomatal closure and maintained significantly higher levels of stomatal conductance (gs) and photosynthetic activity (PN) than the other genotypes even when minimum relative water content (RWC) values were observed. Furthermore, Vg was the only genotype able to accumulate significant amounts of proline already under moderate water deficit, what could explain the lower osmotic potential (ψs) values observed in these plants. The three V. unguiculata cultivars presented a similar stomatal control under increasing water deficit. A mesophyllic impairment of photosynthetic capacity (Pmax) was detected for cv. 1183 from the beginning of drought onset (85-75 % RWC) while in the Vg plants the values remained unaffected along the whole drought period, indicating that PN decrease observed in this genotype is mainly a consequence of stomatal closure. Such Pmax maintenance suggests the existence of a high mesophyllic ability to cope with increasing tissue dehydration in Vg.

Diurnal courses in net photosynthetic rate (PN), stomatal conductance (gs), leaf water potential (ψ), internal CO2 concentration (ci), and water use efficiency (WUE) were studied as season progressed, in relation to environmental factors in field grown Prunus amygdalus. In sun leaves PN reached maximum between 09:00 to 11:00 h and subsequently declined when high temperature and low humidity occurred. An increase was observed late in the afternoon. A decrease in gs and ψ was found as season progressed in both years of measurements. In periods of high evaporative demand, ψ was very low, however, it did not explain the reductions of PN in all the three periods (spring, early and late summer). Midday depression of PN and gs seemed to be related with leaf temperature (Tl) and high irradiance. Increase in ci and F0 and decrease in Fv/Fm found between 12:00 and 14:00 h corresponded to the decrease in PN. Therefore, a transient modification of photosynthetic machinery might be considered. WUE was negatively correlated with vapour pressure difference of leaf to air, that decreased during the day. The September values, higher than in the previous months, were due to the lower seasonal decreases in PN than in gs.

Five cultivars of Prunus amygdalus Batsch (Ferragnes, Ferrastar, Marcona, Garrigues, and Non Pareil) grafted on two different rootstocks (Garrigues and GF677), and two cultivars (Ferraduel and Casa Nova) grafted on GF677, were grown for three years under rainfed conditions in an orchard in northeast Portugal. Net photosynthetic rate (PN), leaf conductance for water vapour (gs), leaf water potential (Ψ), instantaneous water use efficiency (WUE), and internal CO2 concentration (Ci) were measured at three periods of the growing season: spring, summer (June or July) and late summer (September) over two years. Ferraduel, Ferrastar, and Marcona presented the best performance in the periods when environmental conditions were not very hard (May or September). Casa Nova and Non Pareil were well adapted to high air evaporative demand, preventing the increase of leaf temperature (T1). Ferrastar, although having a good performance in May and September, did well adapt to hard climatic conditions in June 1994. In the following year, although it presented the highest T1, the values were not limiting (30.6 ± 2.1 °C), and PN was only decreased from May to July. Marcona was highly dependent on T1, but prevented its increasing. Garrigues showed lower PN in most measurement periods. GF677 frequently induced the highest PN, WUE, and Ψ. PN was mainly dependent on T1, radiation, Ci, month, and year. WUE depended on the same factors. Ψ depended mainly on gs, air temperature, month, and year.

Photosynthetic capacity (PC) of three peanut cultivars (Arachis hypogaea L. cvs. 57-422, 73-30, and GC 8-35) decreased during drought stress (decline in relative water content from ca. 95 to 70 %) and recovered two days after rewatering. Mild water stress was not limiting for the total ribulose-1,5-bisphosphate carboxylase/oxygenase activity, since this enzyme activity increased under drought. Photosystem (PS) 2 and PS1 (the latter only in cv. GC 8-35) electron transport activities decreased under drought. The ratio of the variable to maximal chlorophyll fluorescence (Fv/Fm) decreased mainly in the cv. GC 8-35. All cultivars showed decreases in photochemical quenching (qP) and quantum yield of PS2 electron transport (Φe). Increase of basal fluorescence (F0) was observed in the cvs. 73-30 and GC 8-35, while the cv 57-422 showed a decrease. After rewatering a sharp increase was observed in the majority of the parameters. Thus under the present stress conditions, the cv GC 8-35 was the most affected for all the parameters under study. The cv. 57-422 showed a higher degree of tolerance being gradually affected in photosynthetic capacity (PC) in contrast to the two other cvs. which showed a sharp decrease in PC at the beginning of the drought cycle.

Biologia plantarum, an international journal for experimental botany founded in 1959 by Professor Bohumil Němec. Covers all branches of experimental botany ranging from molecular biology and biotechnology to whole-plant and stand functioning.

SummaryWhen water is limiting plant growth, will it be essential to increase protoplasmic drought resistance (PDR) in order to improve water use efficiency (WUE)? Such subject is obviously of utmost importance for semi-arid tropical and mediterranean zones.Water deficit brings a decrease (d) to net photosynthetic rate (A) by means of a "stomatal" (s) and/or a, so-called, "non-stomatal" effect (p). Disregarding minor factors, one can write: d = Ao—A1 = s + p + i where i represents the interaction between the determinant factors of s and p, and Ao and A1, are the values of A before and after drought stress.Since the remarkable work of Cowan and Farquhar, at the beginning of the eighties it was almost generally accepted that p ≫ s.But the discovery of a "patchyness" phenomenon on induced stomatal closure, raised the possibility of a different perspective.We will tackle the problem under discussion as follows: 1) General formulation: The deterministic chain involving s, p, and their determinants is designed. The interaction factor i is necessary in this context.2) As water deficit progresses, when does p begin to become important? Is it also important under field agricultural conditions? Experimental results embodied in a framework give the answer to such questions: s comes normally first; for C3 plants p becomes critical just for Relative Water Deficit (RWD) valves higher than the critical "Kaiser belt" (30–40% RWD). Evidence is presented about the agricultural and ecological importance of p in the above mentioned climatic zones.3) Searching for an intrinsic index for the degree of protoplasmic strain: Can c1 (the internal CO2 concentration in the Cowan's sense) be used as such an index? It will be demonstrated that c1 = (r2 + δ) A +r2 R1 where r2 is a quasi-ohmic resistance to the CO2 flux from the point of effective junction of the CO2 respiratory flow (the intensity of which is given by R) to the photosynthetic one, and δ an anatomical resistance. It is now obvious that c1 is too ambiguous to be used as the searched index. We propose, instead, that such index can be played by r2 that includes the addition in series of the carboxilating and photoreducing resistances.4) Considering patchyness, we present first the Cornic's view on this matter and consider next the contribution of that phenomenon in explaining the commonly accepted view of a secondary role of stomata in the decrease d caused by drought on photosynthesis. But the interaction i, usually forgotten in this kind of studies, must also be considered, (i is generally negative). Other possible causes are discussed. A simple diaggnosis method for the detection of patchyness when RWD < 30–40% will be proposed.5) Our work with Myrothamnus flabelifolia (a "ressurrection" plant) sheds some light into this discussion. Plants with PDR have no need to re-build drought strained structures, but just to reactivate them by re-hydration. We try to design a quantitative criterion for PDR.6) Under heavy drought stress conditions to improve WUE or to keep it at reasonable levels, PDR becomes essential. Case-studies are presented, including biomass estimates. The proper conditions for WUE increase under stomatal closure are presented and discussed.7) An operational criterium to breeding selection is proposed.

SUMMARY - Daily and seasonal gas exchange of fourteen rainfed almond tree varieties grafted in GF677, six years old, was monitored in the field. Pre-dawn leaf water potential (ψ0) changed from about -0.5 MPa in May to ca. -1.2 MPa in October which shows a reduction in soil water availability despite some precipitation in the first days of October. As a consequence, net photosynthesis (Pn) and stomatal conductance (Gs) decreased in the same period for most varieties, although it did not in 'José Dias' and 'Duro d'Estrada'. Decreases in Pn and Gs were observed from morning to afternoon in both periods. Pn maintained reasonably high values after harvest (≥ ≥ ≥ ≥10 µmol/m 2 .s) in all varieties which can be ascribed to increases or maintenance of pressure potential in some varieties. Although low, the precipitation in the first days of autumn and the increases in soluble sugars and /or proline could have contributed to maintain plant water status and photosynthetic activity. Increases of WUEi were observed in 'Duro d' Estrada', 'Duro Italiano', 'José Dias' and 'Verdeal'. Overall, the Portuguese variety 'José Dias' showed the best photosynthetic performance.