F. Tognoni

Involvement of abscisic acid in leaf and root of maize (Zea mays L.) in avoiding chilling-induced water stress

In the present study, we investigated the role of abscisic acid (ABA) on chilling tolerance of maize. Two maize genotypes differing in chilling sensitivity (Z7 tolerant and Penjalinan sensitive) were subjected to chilling (5 8C, 12 h photoperiod, 150 mmol m � 2 s � 1 PPFD) for 3 days under two relative humidity (RH) regimes (60 or 100% RH). Some plants were exogenously treated 24 h before chilling with ABA (100 mM). As expected, high humidity (100% RH) or ABA pre-treatment prevented the leaf water deficit induced by chilling at 60% RH in chilling sensitive Penjalinan plants. ABA pre-treatment improved chilling tolerance of Penjalinan plants, mainly by decreasing leaf conductance and by increasing root water flow. At the leaf level, we found a relationship between ABA content and chilling tolerance in both maize genotypes. No relationship between ABA content and leaf conductance was found. Moreover, during chilling, no differences on leaf conductance between the two genotypes were observed, probably indicating that the different water stress suffered by the two genotypes could be linked to differences in the root water uptake. The rise in leaf ABA content during chilling was independent of the leaf water status, so it must be induced by the low temperature per se, and after a longer cold exposure also by the vapour pressure deficit (VPD) (a higher VPD allows more ABA accumulation). At the root level, we did not observe a relationship between the root hydraulic acclimation to chilling and the root ABA content. Z7 plants chilled at 60% RH had the same root ABA content as those which were chilled at 100% RH and as Penjalinan plants; however, the former showed a higher root hydraulic conductance. The rise in the root ABA content in Z7 plants followed the same pattern as observed in the leaves. In Penjalinan plants, the rise in root ABA content was linked only to low temperatures per se, since it increased in the same way in plants chilled under 60 or 100% RH. # 2003 Elsevier Ireland Ltd. All rights reserved.

Solid phase radioimmunoassay for the quantitation of abscisic acid in plant crude extracts using a new monoclonal antibody.

Summary A new mouse monoclonal antibody against abscisic acid (ABA) was produced and characterized. This antibody is highly specific for free (S)-ABA and shows a good affinity constant. A newly developed solid phase radioimmunoassay (RIA) for the quantitation of ABA content in plant extracts is described. This assay proved to be more sensitive and precise than the commonly used liquid phase RIA. Using this assay ABA was quantified in tomato and bean leaves and in Sechium endosperm. Results were compared with those obtained using the other two monoclonal antibodies produced up to now against ABA. Results obtained with RIA were validated by physicochemical methods.

Growth and photosynthesis of Lycopersicon esculentum (L.) plants as affected by nitrogen deficiency

Fully expanded leaves of tomato (Lycopersicon esculentum) growing with either complete or nitrogen-deficient nutrient solution were analysed for leaf water status, gas exchange and chlorophyll fluorescence during the vegetative and reproductive phases. N-deficiency did not affect leaf water relations but did decrease light saturated photosynthetic rate as well as stomatal conductance in the vegetative stage. A lower variable to maximum fluorescence ratio (Fv/Fm) was found in N-limited plants which also showed an increase in leaf starch content and in starch to sucrose ratio. The inhibition of photosynthesis and the alteration of photosynthates partitioning were responsible for the growth reduction in N-stressed plants. During the reproductive phase the limitation of photosynthesis may be due to a large accumulation of starch which determines both a decrease in the carbon demand from the sinks and a decrease in CO2 conductance in the mesophyll.

Modeling Salinity Build-Up in Recirculating Nutrient Solution Culture

Abstract This paper presents a simple model for the changes in ion concentration and electrical conductivity (EC) of the recirculating nutrient solution in a closed-loop soilless culture of tomato (Lycopersicon esculentum Mill.). The model was designed on the basis of a balanced equation for plant nutrient uptake: for macrocations (K+, Mg2+ and Ca2+), a linear dependence of concentration on crop water uptake was assumed, while for non-essential ions, such as sodium (Na+), a non-linear function was used. The model was developed for closed-loop hydroponic systems in which crop water uptake (namely, transpiration) is compensated by refilling the mixing tank with complete nutrient solution. In these systems, EC gradually increases as a result of the accumulation of macro-elements and, principally, of non-essential ions, like Na+, for which the apparent uptake concentration (i.e., the ratio between nutrient and water uptake) is lower than their concentration in the irrigation water. For model calibration, data from both the literature and a previous work were used, while validation was performed with data from original experiments conducted with tomato plants in different seasons and using water with different sodium chloride (NaCl) concentrations (10 and 20 meq/L). The results of validation indicate that the model may be a useful tool for the management of closed-loop hydroponics, because it simulates rather well the salt accumulation that occurs in the recirculating nutrient solution when it is prepared with irrigation water of poor quality. Furthermore, the model is able to estimate the amount of crop evapotranspiration that leads to a value of EC at which flushing is necessary, thus enabling one to predict the water and nitrogen runoff of the semi-closed soilless culture.

Endogenous ethylene requirement for adventitious root induction and growth in tomato cotyledons and lavandin microcuttings in vitro

The role of ethylene in the formation of adventitious roots in vitro was studied in tomato (Lycopersicon esculentum Mill. cv. UC 105) cotyledons and lavandin (Lavandula officinalis Chaix × Lavandula latifolia microshoots. Both systems were able to form roots on hormone-free medium evolving low amounts of ethylene. The addition of 20–50 μM indole-3-acetic acid (IAA) inhibited root formation in tomato cotyledons while increasing ethylene production. Naphthaleneacetic acid (NAA, 3 μM) stimulated root number in lavandin explants and induced a transient rise in ethylene evolution. Enhanced ethylene levels via the endogenous precursors 1-aminocyclopropane-1-carboxylic acid (ACC, 25–50 μM) drastically impaired root regeneration and growth in tomato. In lavandin, 10 μM ACC stimulated ethylene production and significantly inhibited the rooting percentage and root growth. Conversely, ACC enhanced the root number in the presence of NAA only. Severe inhibition of rooting was also caused by ethylene reduction via biosynthetic inhibitors, aminoethoxyvinylglycine (AVG, 5–10 μM) in tomato, and salicylic acid (SA, 100 μM) in lavandin. A strict requirement of endogenous ethylene for adventitious root induction and growth is thus suggested.

Influence of Chilling and Drought on Water Relations and Abscisic Acid Accumulation in Bean

Intact bean seedlings were subjected to either chilling (4°C) or drought stress. Leaf water relations and abscisic acid (ABA) content were monitored throughout a stress-recovery cycle. Chilling at low relative humidity (RH) and drought caused similar water deficits, as indicated by the decline in relative water content and water potentials, but they had different effects on ABA accumulation. There was a rapid increase in ABA levels in the leaves of water-deprived plants while only slight ABA accumulation was observed after 48 h of chilling (4°C). After 24 h cold treatment there were large changes in turgor but no change in ABA content. Plants chilled for 24 h accumulated ABA only when transferred to recovery conditions (20°C, 90-95% RH, in the dark) to an extent that was related to the rate of leaf rehydration. When the chilling treatment was performed in a water-saturated atmosphere, plants did not suffer any water stress and ABA levels did not increase over a period of 48 h. However, when the chilling treatment lasted for a longer period (72 h), a significant increase in ABA levels was found also in the absence of water deficit. Experiments performed with leaf discs incubated in a mannitol solution (osmotic potential - 1.6 MPa) at different temperatures indicated that low temperature markedly inhibits ABA synthesis and that water stress induces increases in ABA content only at non-limiting warm temperatures.

Photosynthetic Activity of Ripening Tomato Fruit

Gas exchanges, chlorophyll (Chl) a fluorescence and carboxylation activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and phosphoenolpyruvate carboxylase (PEPC) were determined in tomato (Lycopersicon esculentum Mill.) fruits picked at different developmental stages (immature, red-turning, mature, and over-ripe). The fruits did not show signs of CO2 fixation. However, photochemical activity was detectable and an effective electron transport was observed, the values of Chl fluorescence parameters in green fruits being similar to those determined in the leaves. The RuBPCO activity, which was similar to those recorded in the leaves at the immature stage of the fruit, decreased as the fruit ripened. PEPC activity was always higher than RuBPCO activity.

Involvement of activated charcoal in the modulation of abiotic and biotic ethylene levels in tissue cultures

Abstract Activated charcoal in the culture medium improved axillary bud proliferation of lavandin and growth of Anemone seedlings, but it negatively influenced root formation. In Anemone, severe medium browning was prevented by activated charcoal (AC). Abiotic ethylene released by the agarized medium was adsorbed by AC, depending upon the culture vessel and the medium volume. Biotic ethylene produced by lavandin nodes, laying directly on the medium surface, was easily adsorbed by AC. On the contrary, Anemone seedlings, 5 cm long, looked healthier in the presence of AC and evolved higher ethylene levels than the control. Therefore, the positive effect of AC on both species cannot be related to ethylene adsorption but probably to the removal of unidentified inhibitory substances from the culture medium.

A comparison between two methods to control nutrient delivery to greenhouse melons grown in recirculating nutrient solution culture

Abstract Two methods to control nutrient delivery to greenhouse melon plants grown with the nutrient film technique were compared: a conventional control system based on the adjustment of electrical conductivity (EC) of the recirculating nutrient solution, and a programmed nutrient addition, which was based simply on pre-established weekly supply of N, P and K without any attempt to maintain constant values of nutrient concentration and EC. The method to control nutrient supply did not influence significantly fruit yield or quality, but the nutrient addition reduced the crop consumption of water, N, P and K by 40–60% with respect to the EC method.

Salt tolerance and mineral relations for celery

Abstract To invertigate the relationship between salt tolerance and plant mineral status in celery (Apium graveolens L.) growth and the concentration of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sodium (Na), and chloride (Cl) in different tissues were determined in plants grown in hydroculture with nutrient solutions containing 5 (control), 50,100, and 300 mM sodium chloride (NaCl) for four weeks. At salinity levels of 50 and 100 mM NaCl, there was a moderate, albeit significantly, reduction of growth, while a drastic decrease in both fresh and dry weight was obtained at 300 mM NaCl. Regardless of the salinity level, growth resumed promptly and completely once the stress was ceased. Sodium chloride stress reduced the accumulation of nitrate (NO3)‐N in all plant tissues, but there were no relevant effects on the concentration of reduced N and P. The concentration of K in roots and leaf petioles was unaffected by NaCl treatment, but it gradually declined with increasing salinity in leaf bla...