Paolo Vernieri

Sugar Repression of a Gibberellin-Dependent Signaling Pathway in Barley Embryos.

Increasing evidence shows that sugars can act as signals affecting plant metabolism and development. Some of the effects of sugars on plant growth and development suggest an interaction of sugar signals with hormonal regulation. We investigated the effects of sugars on the induction of [alpha]-amylase by gibberellic acid in barley embryos and aleurone layers. Our results show that sugar and hormonal signaling interact in the regulation of gibberellic acid-induced gene expression in barley grains. The induction of [alpha]-amylase by gibberellic acid in the aleurone layer is unaffected by the presence of sugars, but repression by carbohydrates is effective in the embryo. [alpha]-Amylase expression in the embryo is localized to the scutellar epithelium and is hormone and sugar modulated. The effects of glucose are independent from the effects of sugars on gibberellin biosynthesis. They are not due to an osmotic effect, they are independent of abscisic acid, and only hexokinase-phosphorylatable glucose analogs are able to trigger gene repression. Overall, the results suggest the existence of an interaction between the hormonal and metabolic regulation of [alpha]-amylase genes in barley grains.

Mycorrhizal and non-mycorrhizal Lactuca sativa plants exhibit contrasting responses to exogenous ABA during drought stress and recovery

The arbuscular mycorrhizal (AM) symbiosis enhances plant tolerance to water deficit through the alteration of plant physiology and the expression of plant genes. These changes have been postulated to be caused (among others) by different contents of abscisic acid (ABA) between AM and non-AM plants. However, there are no studies dealing with the effects of exogenous ABA on the expression of stress-related genes and on the physiology of AM plants. The aim of the present study was to evaluate the influence of AM symbiosis and exogenous ABA application on plant development, physiology, and expression of several stress-related genes after both drought and a recovery period. Results show that the application of exogenous ABA had contrasting effects on AM and non-AM plants. Only AM plants fed with exogenous ABA maintained shoot biomass production unaltered by drought stress. The addition of exogenous ABA enhanced considerably the ABA content in shoots of non-AM plants, concomitantly with the expression of the stress marker genes Lsp5cs and Lslea and the gene Lsnced. By contrast, the addition of exogenous ABA decreased the content of ABA in shoots of AM plants and did not produce any further enhancement of the expression of these three genes. AM plants always exhibited higher values of root hydraulic conductivity and reduced transpiration rate under drought stress. From plants subjected to drought, only the AM plants recovered their root hydraulic conductivity completely after the 3 d recovery period. As a whole, the results indicate that AM plants regulate their ABA levels better and faster than non-AM plants, allowing a more adequate balance between leaf transpiration and root water movement during drought and recovery.

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.

Plant Responses to Drought Stress and Exogenous ABA Application are Modulated Differently by Mycorrhization in Tomato and an ABA-deficient Mutant (Sitiens)

The aims of the present study are to find out whether the effects of arbuscular mycorrhizal (AM) symbiosis on plant resistance to water deficit are mediated by the endogenous abscisic acid (ABA) content of the host plant and whether the exogenous ABA application modifies such effects. The ABA-deficient tomato mutant sitiens and its near-isogenic wild-type parental line were used. Plant development, physiology, and expression of plant genes expected to be modulated by AM symbiosis, drought, and ABA were studied. Results showed that only wild-type tomato plants responded positively to mycorrhizal inoculation, while AM symbiosis was not observed to have any effect on plant development in sitiens plants grown under well-watered conditions. The application of ABA to sitiens plants enhanced plant growth both under well-watered and drought stress conditions. In respect to sitiens plants subjected to drought stress, the addition of ABA had a cumulative effect in relation to that of inoculation with G. intraradices. Most of the genes analyzed in this study showed different regulation patterns in wild-type and sitiens plants, suggesting that their gene expression is modulated by the plant ABA phenotype. In the same way, the colonization of roots with the AM fungus G. intraradices differently regulated the expression of these genes in wild-type and in sitiens plants, which could explain the distinctive effect of the symbiosis on each plant ABA phenotype. This also suggests that the effects of the AM symbiosis on plant responses and resistance to water deficit are mediated by the plant ABA phenotype.

Chlorophyll a Fluorescence as a Tool in Evaluating the Effects of ABA Content and Ethylene Inhibitors on Quality of Flowering Potted Bougainvillea

Flowering potted plants during the postproduction stage are usually stored in inadequate environmental conditions. We evaluated the effect of the most common storage conditions and treatments on two Bougainvillea cultivars after harvest and during recovery. Flowering potted Bougainvillea plants were treated with 100 mL 2 mM amino-oxyacetic acid (AOA) or 500 ppb 1-methylcyclopropene (1-MCP) prior storage in dark at 14°C for simulating transport or storage conditions and, subsequently, transferred to growth chambers at 20°C in the light for one week for evaluating the recovery ability. The plant stress during the experiments was assessed by ethylene, ABA, and chlorophyll a fluorescence measurements. Ethylene production was affected by temperature rather than treatments. ABA concentration declined in leaves and flowers during storage and was not affected by treatments. Fluorescence parameters appear to be very useful for screening Bougainvillea cultivars resistant to prolonged storage periods.

Exogenous ABA accentuates the differences in root hydraulic properties between mycorrhizal and non mycorrhizal maize plants through regulation of PIP aquaporins

The arbuscular mycorrhizal (AM) symbiosis has been shown to modulate the same physiological processes as the phytohormone abscisic acid (ABA) and to improve plant tolerance to water deficit. The aim of the present research was to evaluate the combined influence of AM symbiosis and exogenous ABA application on plant root hydraulic properties and on plasma-membrane intrinsic proteins (PIP) aquaporin gene expression and protein accumulation after both a drought and a recovery period. Results obtained showed that the application of exogenous ABA enhanced osmotic root hydraulic conductivity (L) in all plants, regardless of water conditions, and that AM plants showed lower L values than nonAM plants, a difference that was especially accentuated when plants were supplied with exogenous ABA. This effect was clearly correlated with the accumulation pattern of the different PIPs analyzed, since most showed reduced expression and protein levels in AM plants fed with ABA as compared to their nonAM counterparts. The possible involvement of plant PIP aquaporins in the differential regulation of L by ABA in AM and nonAM plants is further discussed.

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.

Biostimulants and crop responses: a review

Agricultural growing practices have been evolving towards organic, sustainable or environmental friendly systems. The aim of modern agriculture is to reduce inputs without reducing the yield and quality. These goals can be achieved by breeding programmes but would be species specific and time consuming. The identification of organic molecules able to activate plant metabolism may allow an improvement in plant performance in a short period of time and in a cheaper way. Biostimulants are plant extracts and contain a wide range of bioactive compounds that are mostly still unknown. These products are usually able to improve the nutrient use efficiency of the plant and enhance tolerance to biotic and abiotic stresses. In this review, the state of the art and future prospects for biostimulants are reported and discussed. Moreover, particular attention has been paid to intensive agricultural systems such as horticultural and floricultural crops. In vegetables, the application of biostimulants allowed a reduction in fertilizers without affecting yield and quality. In leafy vegetables susceptible to nitrate accumulation, such as rocket, biostimulants have been able to improve the quality and keep the nitrates under the limits imposed by EU regulations. Moreover in leafy vegetables, biostimulants increased leaf pigments (chlorophyll and carotenoids) and plant growth by stimulating root growth and enhancing the antioxidant potential of plants. In floriculture, biostimulants used in bedding plant production stimulated the growth of plants, which reached the blooming and commercial stages earlier, thus optimizing space in the greenhouse.

Expression of a dehydrin gene during embryo development and drought stress in ABA-deficient mutants of sunflower (Helianthus annuus L.)

The synthesis of a particular class of proteins, the dehydrins, is a common response to drought in plants. Dehydrins are known to be synthesized by the cell in response to abscisic acid, which represents a link between environment and nuclear activity, though dehydrin genes may be expressed even constitutively. We have investigated the relationship between abscisic acid (ABA) and accumulation of a dehydrin mRNA in sunflower, in which a dehydrin cDNA (HaDhn1a) was isolated. In particular, we studied changes in the steady-state level of dehydrin transcripts in two mutants for ABA synthesis and accumulation: nd-1 (an albino, non-dormant and lethal mutant with a very low ABA content and no ABA accumulation in response to stress) and w-1 (a wilty mutant, with reduced ABA accumulation) during embryo and plantlet development and drought stress. Differences between genotypes were observed through embryogenesis: w-1 shows a lower content of dehydrin transcripts in the early stages compared to control plants, indicating that ABA affects dehydrin mRNA accumulation; however, dehydrin transcripts level appears independent of ABA content in late embryogenesis. Also during drought stress in w-1 adult leaves, ABA is not quantitatively related to the steady-state level of the HaDhn1a transcripts. Finally, data on nd-1 mutant show a high level of dehydrin transcripts after drought stress in plantlet cotyledons and leaflets. These results indicate the existence of two regulation pathways of HaDhn1a transcripts accumulation, an ABA-dependent and an ABA-independent one, which may have cumulative effects.

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.