Kalanchoe blossfeldiana plants expressing the Arabidopsis etr1-1 allele show reduced ethylene sensitivity

Transgenic Kalanchoe blossfeldiana Poelln. with reduced ethylene sensitivity in flowers was obtained by Agrobacterium tumefaciens-mediated transformation using the plasmid pBEO210 containing the mutant ethylene receptor gene etr1-1 from Arabidopsis thaliana under the control of the flower-specific fbp1-promoter from Petunia. Three ethylene-resistent T0 lines, 300, 324 and 331, were selected and analyzed for postharvest-performance and morphological characteristics. Line 324 was found to be infertile and only slightly less ethylene-sensitive than control-plants, but lines 300 and 331 had significantly increased ethylene-resistance and were fertile. These two lines were analyzed for copy-number of the etr1-1 gene by Southern blotting and were crossed with the ethylene-sensitive cultivar ‘Celine’ to create T1 progeny. Line 300 contains two T-DNA copies per nucleus, one of which is rearranged, and these are unlinked according to segregation data from the crossing to ‘Celine’ and PCR-analysis of progeny plants. For control plants all flowers were closed after 2 days at 2 μl l⁻¹ ethylene, but for line 300 only 33% were closed after 10 days. Line 331 contains three T-DNA copies per nucleus and is more sensitive to ethylene than line 300. In the line 300 the etr1-1 gene was found by RT-PCR to be expressed in petals and stamens but not in carpels and sepals. Both lines 300 and 331, and their progeny, appear morphologically and physiologically identical to control plants except for the higher ethylene resistance. Line 300 and its progeny with only one T-DNA copy have very low ethylene sensitivity and may be useful in future breeding.     

Changes in photosynthetic rates and growth following root treatments of tomato plants with phytohormones

The effects of root applications of kinetin, gibberellic acid (GA₃) and indoleacetic acid (IAA) on photosynthesis was measured using an open infrared CO₂ gas-exchange system. There was a 30–35% increase in the photosynthetic rates (mg CO₂/dm²/hr) of attached leaves within 8 hr following root treatment with 0.47 M kinetin. On a short-term basis (up to 2 days) 0.47 M kinetin was shown to have the optimal stimulatory effect on photosynthesis, relative growth rate (RGR) and total plant dry weight. If the roots were in contact with 0.47 M kinetin for longer than two days there was severe branching of the root system and growth was severely decreased. When plants were left in contact with the kinetin treatment for up to 7 days the optimal stimulatory concentration was considerably lower (0.0047 M) . Plants receiving a 4, 8, or 12 hr pulse with 0.47 M kinetin to the roots exhibited higher leaf photosynthetic rates than the control. Plants receiving an 8 or 12 hr pulse with 0.47 M kinetin maintained photosynthetic rates higher than the control for the duration of the experiment (8 days) while the 4 hr pulse remained higher than the control for only 5 days. A sharp decrease in the photosynthetic rate, RGR and total plant dry weight was observed two days following continual treatments with 0.47 M kinetin to the roots. At low light levels there was approximately a 100% increase in the photosynthetic rate two days following treatment with 0.47 M kinetin while at a saturating irradiance there was a 30 to 35% increase. Indoleacetic acid either showed no effect on the photosynthetic rate, RGR and total plant dry weight or an inhibitory effect was observed. Either GA₃ or kinetin alone were shown to stimulate photosynthesis, RGR and total plant dry weight, however, when GA₃ at a 1.4 M concentration was applied in combination with kinetin at a 0.0047 M concentration to the roots of tomato plants there was no additive effect. In all cases kinetin dramatically reduced leaf resistance whereas GA₃ had no effect.By supplying either GA₃ or kinetin to the roots of tomato plants a highly reproducible stimulation in the photosynthetic rate, RGR and total plant dry weight can be achieved at physiologically relevant concentrations, whereas IAA appears to have an inhibitory effect.Approved for publication on July 29, 1981 as paper number 6281 in the journal series of the Pennsylvania Agricultural Experiment Station.Research Assistant and Assistant Professor, respectively.     

The temperature-related photosynthetic capacity of plants under desert conditions

Summary As described earlier, the native arido-active perennial Hammada scoparia and the cultivated Prunus armeniaca exhibit characteristic seasonal shifts of their temperature optimum of net photosynthesis (OP) under desert conditions in the Negev. In the present paper the OP values were compared with the actual tissue temperatures of the experimental plants.During the growing period from March to September the duration of optimal temperatures for net photosynthesis (OP±3°C) experienced by the plants was 32.2% of the total time at light saturation for P. armeniaca and 27.8% for H. scoparia. For optimal photosynthesis the branchlets of H. scoparia are too cold for 66.1% of the time span and too warm for 6.1% of the time. The respective values for the leaves of the apricot are 28.6% and 39.2%. Simulations at changed tissue temperature show, that for P. armeniaca neither a higher nor a lower temperature regime would lengthen the time span for optimal thermal conditions. For H. scoparia, however, an increase of the general temperature level by 6°C would considerably improve the temperature-related photosynthetic efficiency. The natural temperature responses of the plants were compared with simulations using OP values which are supposed not to shift but to stay constant from March through September at their spring minimum, their summer maximum, or at an intermediate value. For P. armeniaca such constant OP values would result in a shorter duration of optimal temperature conditions. With this plant the natural seasonal shift of the temperature characteristics appears to provide an advantage in respect to its photosynthetic capacity. Contrary to this, for H. scoparia a constant OP value at the low spring level or even at the intermediate level during all the season would result in a substantially prolonged period of favourable temperature conditions for photosynthesis. In this case the seasonal change of optimum temperature for photosynthesis with higher OP values in summer signifies a disadvantage with respect to the temperature-related photosynthetic capacity at the habitat in the central Negev. Apparently this C₄ plant is adapted to higher temperatures than were present. It appears that acclimations of native plants are not always beneficial.     

Increased heat sensitivity of photosynthesis in tobacco plants with reduced Rubisco activase

High temperature inhibits photosynthesis by several mechanisms including deactivation of Rubisco. The inhibition of photosynthesis by high temperature and its relationship to Rubisco deactivation was studied using tobacco (Nicotiana tabaccum L. cv W38) transformed with a Rubisco activase gene inserted in the antisense orientation and untransformed controls. High temperature (42 °C) reduced photosynthesis in both lines of plants. However, photosynthesis recovered nearly completely in wild-type plants and very little in plants lacking Rubisco activase. The F₀ level of chlorophyll fluorescence decreased and q_N increased in the control plants during heating. In the antisense plants, q_N was always high and F₀ increased slightly during heat stress. NADP-malate dehydrogenase activation was unaffected by heat stress in control plants but was increased in the transgenic plants, consistent with a high redox status in the chloroplast. In wild-type plants, the inhibition of photosynthesis could be explained by a reversible decarbamylation of Rubisco and an acceptor-side limitation imposed on photosynthetic electron transport. However, in the anti-activase plants, carbamylation was low and constant and could not explain how photosynthesis was reduced at high temperature. Because ribulose bisphosphate was saturating at high temperature, the reduction in photosynthesis must have been caused by some impairment of Rubisco function not reflected in measurements of activation state or carbamylation status. This in vivo Rubisco impairment was not relieved upon return to lower temperature. We speculate that the reversible decarbamylation of Rubisco at moderately high temperature may be a protective mechanism by which the plant avoids more serious effects on Rubisco and the rest of the photosynthetic apparatus.This revised version was published online in October 2005 with corrections to the Cover Date.     

Expression of a luteoviral movement protein in transgenic plants leads to carbohydrate accumulation and reduced photosynthetic capacity in source leaves

Elucidating the role of viral genes in transgenic plants revealed that the movement protein (MP) from tobacco mosaic virus is responsible for altered carbohydrate allocation in tobacco and potato plants. To study whether this is a general feature of viral MPs, the movement protein MP17 of potato leafroll virus (PLRV), a phloem-restricted luteovirus, was constitutively expressed in tobacco plants. Transgenic lines were strongly reduced in height and developed bleached and sometimes even necrotic areas on their source leaves. Levels of soluble sugars and starch were significantly increased in source leaves. Yet, in leaf laminae the hexose—phosphate content was unaltered and ATP reduced to only a small extent, indicating that these leaves were able to maintain homeostatic conditions by compartmentalization of soluble sugars, probably in the vacuole. On the contrary, midribs contained lower levels of soluble sugars, ATP, hexose—phosphates and UDP-glucose supporting the concept of limited uptake and catabolism of sucrose in the phloem. The accumulation of carbohydrates led to a decreased photosynthetic capacity and carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) probably owing to decreased expression of photosynthetic proteins. In parallel, levels of pathogenesis-related proteins were elevated which may be the reason for the obtained limited resistance against the unrelated potato virus Y (PVY)^N in the transgenic tobacco plants. Ultrathin sections of affected leaves harvested from 2-week-old plants revealed plasmodesmal alterations in the phloem tissue while plasmodesmata between mesophyll cells were indistinguishable from wild-type. These data favour the phloem tissue to be the primary site of PLRV MP17 action in altering carbohydrate metabolism.     

Involvement of plant growth substances in the alteration of leaf gas exchange of flooded tomato plants

Ethylene, abscisic acid, and cytokinins were tested for their ability to either induce or prevent the changes which occur in gas exchange characteristics of tomato (Lycopersicon esculentum Mill. cv. Rheinlands Ruhm) leaves during short-term soil flooding. Ethylene, which increases in the shoots of flooded plants, had no effect on stomatal conductance or photosynthetic capacity of drained plants. Abscisic acid, which also accumulates in the shoots of flooded plants, could reproduce the stomatal behavior of flooded plants when sprayed on the leaves of drained plants. However, photosynthetic capacity of drained plants was unaffected by abscisic acid sprays. Cytokinin export from the roots to the shoots declines in flooded plants. Spray applications of benzyladenine increased stomatal conductance in both flooded and drained plants. In addition, the decline in photosynthetic capacity during flooding was largely prevented by supplementary cytokinin applications. The possible involvement of these growth substances in modifying leaf gas exchange during flooding is discussed.     

Stomatal conductance does not correlate with photosynthetic capacity in transgenic tobacco with reduced amounts of Rubisco

High-resolution imaging of chlorophyll a fluorescence from intact tobacco leaves was used to compare the quantum yield of PSII electron transport in the chloroplasts of guard cells with that in the underlying mesophyll cells. Transgenic tobacco plants with reduced amounts of Rubisco (anti-Rubisco plants) were compared with wild-type tobacco plants. The quantum yield of PSII in both guard cells and underlying mesophyll cells was less in anti-Rubisco plants than in wild-type plants, but closely matched between the two cell types regardless of genotype. CO2 assimilation rates of anti-Rubisco plants were 4.4 micromol m(-2) s(-1) compared with 17.3 micromol m(-2) s(-1) for the wild type, when measured at a photon irradiance of 1000 micromol m(-2) s(-1) and ambient CO2 of 380 micromol mol(-1). Despite the large difference in photosynthetic capacity between the anti-Rubisco and wild-type plants, there was no discernible difference in the rate of stomatal opening, steady-state stomatal conductance or response of stomatal conductance to ambient CO2 concentration. These data demonstrate clearly that the commonly observed correlation between photosynthetic capacity and stomatal conductance can be disrupted in the long term by manipulation of photosynthetic capacity via antisense RNA technology. It was concluded that stomatal conductance is not directly determined by the photosynthetic capacity of guard cells or the leaf mesophyll.     

Inhibition of ethylene synthesis in tomato plants subjected to anaerobic root stress

Enhanced ethylene production and leaf epinasty are characteristic responses of tomato (Lycopersicon esculentum Mill.) to waterlogging. It has been proposed (Bradford, Yang 1980 Plant Physiol 65: 322-326) that this results from the synthesis of the immediate precursor of ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC), in the waterlogged roots, its export in the transpiration stream to the shoot, and its rapid conversion to ethylene. Inhibitors of the ethylene biosynthetic pathway are available for further testing of this ACC transport hypothesis: aminooxyacetic acid (AOA) or aminoethoxyvinylglycine (AVG) block the synthesis of ACC, whereas CO²⁺ prevents its conversion to ethylene. AOA and AVG, supplied in the nutrient solution, were found to inhibit the synthesis and export of ACC from anaerobic roots, whereas Co²⁺ had no effect, as predicted from their respective sites of action. Transport of the inhibitors to the shoot was demonstrated by their ability to block wound ethylene synthesis in excised petioles. All three inhibitors reduced petiolar ethylene production and epinasty in anaerobically stressed tomato plants. With AOA and AVG, this was due to the prevention of ACC import from the roots as well as inhibition of ACC synthesis in the petioles. With Co²⁺, conversion of both root- and petiole-synthesized ACC to ethylene was blocked. Collectively, these data support the hypothesis that the export of ACC from low O₂ roots to the shoot is an important factor in the ethylene physiology of waterlogged tomato plants.     

Role of ethylene in alleviation of cadmium-induced photosynthetic capacity inhibition by sulphur in mustard

Sulphur (S) assimilation leads to the formation of glutathione (GSH) and alleviation of cadmium (Cd) stress. GSH is synthesized from its immediate metabolite cysteine, which also serves as a metabolite for ethylene formation through S‐adenosyl methionine. To assess the role of ethylene in S‐induced alleviation of Cd stress on photosynthesis, the effects of S or ethephon (ethylene source) on GSH and ethylene were examined in mustard (Brassica juncea L. cv. Varuna). Sufficient‐S at 100 mg S kg^?1 soil alleviated Cd‐induced photosynthetic inhibition more than excess‐S (200 mg S kg^?1 soil) via ethylene by increased GSH. Under Cd stress, plants were less sensitive to ethylene, despite high ethylene evolution, and showed photosynthetic inhibition. Ethylene sensitivity of plants increased with ethephon or sufficient‐S, triggering the induction of an antioxidant system, and leading to increased photosynthesis even under Cd stress. The effects of ethephon and S under Cd stress were similar. The effects of S were reversed by ethylene biosynthesis inhibitor, aminoethoxyvinylglycine (AVG), suggesting that ethylene plays an important role in S‐induced alleviation of Cd stress on photosynthesis.     

The mechanisms of photosynthetic inhibition and the development of scorch in tomato plants treated with spray oils

Photosynthetic inhibition and the development of scorch in tomatoes (cv. Minibelle) were investigated after spraying 3-wk-old plants with oils of viscosities 32-00 and 2–37 cSt (at 22 °C) in controlled conditions in a glasshouse. Environmental conditions (15–25 ± 2 °C, 60–90 ±10% r.h., 100–6000 lux) during spraying did not affect the degree of photosynthetic inhibition but were important in determining the development of scorch. Increasing the spray volume from 0–7 to 14.0 μl/plant (c. 13–260 nl/cm² leaf surface area) increased the severity of scorch in the environmental conditions in which it occurred. The major cause of photosynthetic inhibition by oil appeared to be interstomatal penetration of the cuticle and a mechanism is proposed for scorch involving direct penetration of open stomata by oil droplets.     

Ionic and pH signalling from roots to shoots of flooded tomato plants in relation to stomatal closure

Soil flooding damages shoot systems by inhibiting root functioning. An example is the inhibition of water uptake brought about by decreased root hydraulic conductance. The extent of any resulting foliar dehydration this causes is limited by partial stomatal closure that begins within 4 h and is maintained for several days. Root to shoot signals that promote closure in flooded tomato plants have remained elusive but may include changes in solute delivery to the shoot by transpiration. Accordingly, we examined total osmolites and selected mineral ions in samples of xylem sap flowing at rates approximating whole plant transpiration. After 2.5 h flooding,delivery of total osmolites and of PO₄ ^3-SO₄ ^2-Ca²⁺K⁺NO₃ ^– and H⁺strongly decreased while Na⁺ remained excluded. Several hours later, deliveries of osmolites, PO₄ ^3-, SO₄ ^2-, Ca²⁺, and Na⁺ rose above control values, suggesting that, after approximately 10 h, root integrity became degraded and solute uptake de-regulated. Deliveries of NO₃ ^– remained below control values. Reducing or eliminating the supply of K⁺ to detached leaves to test the potential of decreased K⁺ delivery to close stomata proved negative. Decrease in H⁺ delivery was associated with sap alkalisation. However, raising the pH of buffer from 6.0 or 6.5 to 7.0 did not close stomata when tested in the presence of abscisic acid (ABA) at a concentration (10 mol m^–3) typical of the transpiration stream of flooded plants. It is concluded that despite their rapidity and scale, negative messages in the form of increased pH and decreased solute delivery from roots to shoots are, themselves, unlikely initiators of stomatal closure in flooded tomato plants.     

Effect of melatonin priming on photosynthetic capacity of tomato leaves under low-temperature stress

Melatonin has different functions in plant growth and development, especially in the protection of plants suffering from various forms of abiotic stress. We explored the effect of melatonin priming on photosynthetic activity of tomato (Lycopersicon esculentum L.) leaves. Our results showed that 100 µM is the optimal concentration used for alleviation of the damage to photosynthetic apparatus. Melatonin priming both in the form of leaf spray and direct root application was found to reduce the damage to photosynthetic apparatus, and increase the electron transfer rate and quantum yield of PSI and PSII photochemistry, to protect the thylakoid membrane from damage caused by low-temperature stress. Our study provides fundamental information for further research on the molecular mechanism of melatonin function in regulating photosynthesis.     

High photosynthetic capacity of Sahelian C3 and C4 plants

Photosynthesis Research - The semi-arid ecosystems of the African Sahel play an important role in the global carbon cycle and are among the most sensitive ecosystems to future environmental...     

Increased photosynthetic rates following gibberellic acid treatments to the roots of tomato plants

This study was conducted to evaluate the effects of root applications of gibberellic acid (GA₃) on photosynthesis in tomato plants grown hydroponically. Photosynthetic rates (mg CO₂/dm²/hr) determined using an open infrared CO₂ gas exchange system showed a 40–50% increase within 5 hr after treatment with a 1.4 µM gibberellic acid (GA₃) to their roots. The effect was shown to persist for the duration of the experiment (9 days). Plants receiving pulses of 1.4 µM GA₃ to the roots for 1, 4, 8 or 12 hr exhibited significantly higher photosynthetic rates than the control for 6 days following treatment. By day 9 however, there was no significant difference. Continual treatments with 1.4 µM GA₃ to the roots maintained the photosynthetic rate significantly higher than the control for the duration of the experiment. Interestingly, at the lower light levels the percent stimulation was more dramatic. There was approximately a 90% increase in the photosynthetic rate at 80 µE m^-2 s^-1 while at saturating light conditions (560 µE m^-2 s^-1) there was approximately a 40% increase over the control rate. The light saturation point for both treated and control plants was 240 µE m^-2 s^-1. Applications of physiologically relevant concentrations of GA₃ to the roots of tomato plants stimulates photosynthesis more consistently than that achieved by previous studies involving foliar absorption.Approved for publication on May 28, 1981 as paper number 6242 in the Journal series of the Pennsylvania Agricultural Experiment Station.     

Changes in biomass and photosynthetic parameters of tomato plants exposed to trivalent and hexavalent chromium

Tomato plants were treated for two weeks with different concentrations of Cr(III) or Cr(VI) compounds to compare their toxic effects. The concentration of total Cr in plant tissues increased linearly with its concentration in the growth medium and Cr accumulated largely in the roots, regardless of the form in which it was supplied to the plant. All measured plant growth parameters were negatively affected by Cr, but Cr(VI) showed much more pronounced toxic effects. Leaf net photosynthetic rate (P_N) was decreased by both Cr forms, and the decrease was also greater for Cr(VI). Cr(III) caused no significant effect on leaf stomatal conductance, whereas Cr(VI) reduced it. Cr(VI) also markedly reduced the variable to maximum chlorophyll a fluorescence ratio, measured in dark-adapted leaves.     

The impact of reduced vacuolar invertase activity on the photosynthetic and carbohydrate metabolism of tomato

The impact of reduced vacuolar invertase activity on photosynthetic and carbohydrate metabolism was examined in tomato (Solanum lycopersicon L.). The introduction of a co-suppression construct (derived from tomato vacuolar invertase cDNA) produced plants containing a range of vacuolar invertase activities. In the leaves of most transgenic plants from line INV-B, vacuolar invertase activity was below the level of detection, whereas leaves from line INV-A and untransformed wild-type plants showed considerable variation. Apoplasmic invertase activity was not affected by the co-suppression construct. It has been suggested that, in leaves, vacuolar invertase activity regulates sucrose content and its availability for export, such that in plants with high vacuolar invertase activity a futile cycle of sucrose synthesis and degradation takes place. In INV-B plants with no detectable leaf vacuolar invertase activity, sucrose accumulated to much higher levels than in wild-type plants, and hexoses were barely detectable. There was a clear threshold relationship between invertase activity and sucrose content, and a linear relationship with hexose content. From these data the following conclusions can be drawn. (i) In INV-B plants sucrose enters the vacuole where it accumulates as hydrolysis cannot take place. (ii) There was not an excess of vacuolar invertase activity in the vacuole; the rate of sucrose hydrolysis depended upon the concentration of the enzyme. (iii) The rate of import of sucrose into the vacuole is also important in determining the rate of sucrose hydrolysis. The starch content of leaves was not significantly different in any of the plants examined. In tomato plants grown at high irradiance there was no impact of vacuolar invertase activity on the rate of photosynthesis or growth. The impact of the cosuppression construct on root vacuolar invertase activity and carbohydrate metabolism was less marked.Abbreviations CaMV Cauliflower Mosaic Virus - WT wild type