José Beltrano

Drought Stress Syndrome in Wheat Is Provoked by Ethylene Evolution Imbalance and Reversed by Rewatering, Aminoethoxyvinylglycine, or Sodium Benzoate

Abstract. In this work we present evidence that the drought stress syndrome in the flag leaves and ears of wheat plants, provoked by the production of ethylene (shortening the grain filling period and lowering the grain weight) is reversed by the application of a free radical scavenger, sodium benzoate or the ethylene synthesis inhibitor, aminoethoxyvinylglycine. Rehydration by watering also attenuated the detrimental effect of the water deficit. Consequently, the grain filling period was longer, the grain weight increased, and the total protein content was higher than that in plants watered regularly.

Ethylene as promoter of wheat grain maturation and ear senescence

This work was aimed at testing the involvement of ethylene in the maturation of grain and senescence of the foliar structures of the wheat inflorescence. Whole wheat ears emitted ethylene to the atmosphere. From pre-anthesis, ethylene emission progressively increased from 0.76 nl g−1FW h−1 to a peak 1.53 nl g−1FW h−1 at the hard dough stage of the grains, to fall to a minimum of 0.10 nl g−1FW h−1 at the dormant seed stage. Ethephon increased the ethylene release, hastened the process of grain maturation and senescence of the ears. Aminoethoxyvinylglycine and silver thiosulfate produced the opposite effects. It is concluded that ethylene plays a role in grain maturation and in the senescence of the green bracts of the inflorescence.

Improved tolerance of wheat plants (Triticum aestivum L.) to drought stress and rewatering by the arbuscular mycorrhizal fungus Glomus claroideum: effect on growth and cell membrane stability

O objetivo do trabalho foi pesquisar a contribuicao do fungo micorrizico arbuscular Glomus claroideum a tolerância ao deficit hidrico em plantas de trigo cultivadas sob condicoes controladas em uma câmara de crescimento, submetidas ao estresse hidrico moderado ou severo e reidratacao. A tolerância das plantas ao estresse hidrico foi determinada mediante o peso seco total, conteudo relativo de agua foliar, extravasamento de solutos e concentracoes foliares de clorofilas e proteinas totais nas plantas de trigo micorrizadas e nao-micorrizadas. O peso seco total e a concentracao de clorofila foram significativamente maiores nas plantas micorrizadas sob estresse hidrico moderado ou severo, quando comparadas com as nao-micorrizadas. O extravasamento de solutos foi significativamente menor nas plantas inoculadas estressadas. O conteudo relativo de agua foliar e a concentracao de proteinas totais nas plantas inoculadas aumentaram apenas em condicoes de estresse hidrico severo. Apos a re-irrigacao, nas plantas micorrizadas, houve aumento do peso seco total e da concentracao de clorofilas, alem da recuperacao da integridade das membranas celulares, quando comparadas com as plantas nao-micorrizadas. Em suma, a colonizacao das raizes por G. claroideum poderia ser uma estrategia adequada para reduzir os efeitos deleterios do estresse hidrico e retardar a sindrome da senescencia em trigo.

Effects of arbuscular mycorrhiza inoculation on plant growth, biological and physiological parameters and mineral nutrition in pepper grown under different salinity and p levels

A study was conducted in a greenhouse, to investigate the effects of arbuscular mycorrhizal fungi (Glomus intraradices), soil salinity and P availability on growth (leaf area and dry weight), nutrient absorption and ion leakage, chlorophyll, soluble sugar and proline content and alkaline phosphatase activity of pepper plants (Capsicum annuum L.). Plants were grown at four levels of salinity (0, 50, 100 and 200 mM NaCl) and two P levels (10 and 40 mg kg -1 ). Colonisation was 80% to 51% in non-stressed and high salt-stressed plants, respectively. The mycorrhizal dependency was high and only reduced at the higher salinity level. Mycorrhizal plants maintained greater root and shoot biomass at all salinity levels compared to non-mycorrhizal plants, regardless the P level. Interactions between salinity, phosphorous and mycorrhizae were significant for leaf area, root and shoot dry mass. Non-mycorrhizal plants accumulated higher Na and lower K and P compared to mycorrhizal plants. The cell membrane integrity was greater in mycorrhizal plants than in non-mycorrhizal ones. The proline content increases with increasing salt stress and was significantly higher in leaves than in roots The results indicate that the mycorrhizal inoculation is capable of alleviating the damage caused by salt stress conditions on pepper plants, to maintaining the membranes stability and plant growth, and this could be related to P nutrition.

Senescence of flag leaves and ears of wheat hastened by methyl jasmonate

Abstract. Treatment of flag leaves and ears of wheat plants with MJ (jasmonic acid methylester) (10−5 and 10−4m) did not increase ethylene production, but it did accelerate senescence as indicated by the loss of chlorophyll. MJ also caused the closure of stomata, and consequently the rates of transpiration and photosynthesis decreased. Early maturity shortened the grain filling period, so the thousand grain weight was lower. Although ethylene elicited the same physiologic effects, the syndrome of senescence by MJ is independent of the former. We conclude that senescence and death in wheat are far from being elucidated; however, MJ and ethylene seem to participate in the phenomenon.

Glyphosate and mycorrhization induce changes in plant growth and in root morphology and architecture in pepper plants (Capsicum annuum L.)

Summary Mycorrhizal symbiosis is the mutually beneficial association between the roots of most land plants and many soil fungi. Glyphosate is the most commonly used herbicide for effective control of weeds. This broad-spectrum herbicide is exuded by the roots of treated crops and by senescing weeds, and absorbed by new crops, affecting their growth. We therefore examined the effects of glyphosate residues in the soil, and mycorrhization, on plant growth and root morphology in Capsicum annuum L. Plants were either non-inoculated or inoculated with Glomus mosseae, and grown with different concentrations of glyphosate in soil. Pepper plants grown without glyphosate behaved as mycotrophic species. At high doses, glyphosate (6.32 µM) reduced the extent of root colonisation (to 34%) and the percentage of arbuscule formation (to 50%), and inhibited vesicle formation. Alkaline phosphatase activity was not affected by the herbicide. Inoculated plants had a higher biomass, total height, and leaf area. At the highest concentrations, glyphosate-inoculated plants had double the biomass of non-inoculated plants. Chlorophyll and leaf protein contents were higher in inoculated than in non-inoculated plants at all glyphosate concentrations tested. Inoculated plants increased their root area by approx. 50% with or without glyphosate. The interaction of mycorrhization and glyphosate reduced the mitotic index, mitotic activity, and cell length in the root apices. The highest concentration of herbicide inhibited root branching, modified root morphology and root architecture, and affected growth parameters. Pepper plants tolerate high concentrations of glyphosate in the soil. Mycorrhization benefits plant growth and increases the root area, with a high number of lateral roots, regardless of herbicide concentration. Mycorrhization would be a favourable strategy to allow plants to cope with this abiotic stress condition.

Emission of water stress ethylene in wheat (Triticum aestivum L.) ears: effects of rewatering

In this work it has been found that ethylene production increased only slightly under conditions of a moderate or severe water stress. However, the rehydration of the plants at full turgor after desiccation caused a high emission of ethylene. The desiccation would not irreversibly inactivate the enzymes of the ethylene pathway, since rehydration made the synthesis recommence almost immediately. Water deficit also increased the free radical levels and the antioxidant scavengers, such as superoxide dismutase. Free radicals promote the conversion of 1-amino-cyclopropane-1-carboxylic acid to ethylene, then it is logical to think that both chemical species are involved in the phenomenon of the acceleration of the grain maturity before the plant collapses.

Soil drying and rewatering applied at three grain developmental stages affect differentially growth and grain protein deposition in wheat (Triticum aestivum L.)

Water deficits cause large yield losses in wheat. Although anthesis is generally considered the most vulnerable period, water deficit during grain filling can also cause yield losses. The objective of this study was to investigate the effect of water stress and rewatering, at three different grain developmental stages, on physiological and grain filling parameters and on yield components. Wheat plants were subjected to water deficit and rewatering at the watery ripe, milk and soft dough stages. In the flag leaf, water stress decreased the relative water content, the chlorophyll and protein content and increased the leakage of solutes, at all three studied grain filling stages. Water stress at the watery ripe and milk stages reduced the final grain dry mass by 47 % and 20 %, respectively. This reduction was due to a decrease in the grain filling period and to a significant reduction in the maximum rate of grain-fill. Water stress imposed at the watery ripe stage reduced not only the linear growth phase but also its slope; grain number per spike and the 1000-kernel weight were also significantly reduced. SDS-PAGE patterns of grain proteins at the watery ripe stage did not differ between the controls, stressed or rewatered treatments. Protein patterns at the milk stage changed substantially with water stress, mainly for the high molecular weight glutenin subunits and gliadins. Three new bands were observed with apparent molecular weights of 108.5 kDa, 84.8 kDa and 63 kDa. Rewatering reverted water stress effects when it was imposed at the milk stage. Water deficit at the soft dough stage did not have any effect on protein grain patterns.

Effects of foliar applied benzyladenine on grain yield and grain protein in wheat (Triticum aestivum L.)

The effects of foliar applications of nitrogen and benzyladenine (BA) on grain yield and grain protein of wheat grown under field conditions were studied over 2 years with 5 cultivars at 2 locations. Nitrogen (N) at 20 kg.ha−1, and BA at 100 or 800 mg.l−1 were applied alone or combined at pre and post-anthesis; applications of BA at 8 mg.l−1 were also made on individual ears in order to study the effect on cell number. Weekly determinations of the chlorophyll content of the flag leaf were conducted after anthesis to study leaf senescence. At harvest, yield, yield components and grain protein percentage were determined. N and BA applications delayed chlorophyll loss in the flag leaf, but modified neither yield nor yield components. Foliarly applied BA increased grain protein in four of the five cultivars tested. It is concluded that delay of the senescence induced by BA might allow more energy to be available for N uptake by the crop leading to an increase in grain protein.

Inoculation with mycorrhizal fungi modifies proline metabolism and increases chromium tolerance in pepper plants (Capsicum annuum L.)

In general, heavy metals interfere with several physiological processes and reduce plant growth. Plants naturally establish symbiotic associations with soil microorganisms, such as mycorrhizal fungi. The aim of this research was to determine if inoculation with mycorrhizal fungi increases tolerance to Cr, evidenced by growth and biochemical parameters and the effect on roots membranes in Capsicum annum. Plants were either non-inoculated or inoculated with Glomus mosseae or Glomus intraradices, and grown in the presence of different concentration of Cr (K2Cr2O4) in soil. Pepper plants grown without Cr behaved as mycotrophic species. At the highest concentration (200 μM K2Cr2O4), Cr reduced root colonization by G. mosseae or G. intraradices (to 23 and 20% respectively). Moderate and high concentrations of Cr reduced all growth parameters. The interaction of inoculation and Cr increased leaf chlorophyll and proline content while reduced the leaf protein and root proline content. Carotenoid content was not affected by treatments. High Cr concentrations increased significantly electrolytes leakage in roots, either non-inoculated or inoculated plants. At the highest Cr concentration, inoculated plants had double the biomass of non-inoculated plants. Cr content in roots of inoculated plants was significantly higher than in non-inoculated plants. Chromium accumulation was low in leaves and showed no differences between treatments. Mycorrhization increased pepper plant tolerance to Cr in the soil, modifying proline metabolism to assure a more efficient response.